RE: evaluation question
going to be printed, and count how many bytes or characters it produced and make the result available after you exit the region. Heck, if fed a paragraph of text, it could not only print it but create one or more objects containing a detailed analysis including guessing what language it is in, translating it to English, pointing out spelling and grammar errors, and mailing you a copy! You can imagine quite a few side effects of calling print() but again, why would you put the functionality within print() versus in a function you wrote that does all that as well as calling print()? But even assuming you code that properly and rewrite all your code as something like: with capture: print(...) # use chars_written_within_width as a variable created within that holds what you want. Is that really any better than several other ways we have suggested would work such as creating an f-string independently and then printing it which would handle quite a few use cases? If others wish to keep debating this topic or enhancing it, fine. I am not judging but simply expressing the personal opinion that even if I might have more to add, I am not motivated to do so any longer. Then again, I may soon lose the motivation to be part of this forum and take up other hobbies -Original Message- From: Python-list On Behalf Of Weatherby,Gerard Sent: Monday, February 13, 2023 10:16 AM To: python-list@python.org Subject: Re: evaluation question “Why are we even still talking about this?” Because humans are social creatures and some contributors to the list like to discuss things in depth. From: Python-list on behalf of avi.e.gr...@gmail.com Date: Friday, February 10, 2023 at 6:19 PM To: python-list@python.org Subject: RE: evaluation question *** Attention: This is an external email. Use caution responding, opening attachments or clicking on links. *** There are no doubt many situations someone wants to know how long something will be when printed but often at lower levels. In variable-width fonts, for example, the number of characters does not really line up precisely with how many characters. Some encodings use a varying number of bytes and, again, the width of the output varies. So for people who want to make 2-D formatted output like tables, or who want to wrap lines longer than N characters, you more often let some deeper software accept your data and decide on formatting it internally and either print it at once, when done calculating, or in the case of some old-style terminals, use something like the curses package that may use escape sequences to update the screen more efficiently in various ways. If someone wants more control over what they print, rather than asking the print() function to return something that is mostly going to be ignored, they can do the things others have already suggested here. You can make your message parts in advance and measure their length or anything else before you print. Or make a wrapper that does something for you before calling print, perhaps only for common cases and then returns the length to you after printing. I wonder if the next request will be for print() to know what your output device is and other current settings so it return the width your text takes up in pixels in the current font/size ... I add a tidbit that many ways of printing allow you to specify the width you want something printed in such as you want a floating point value with so many digits after the decimal point in a zero or space padded field on the left. So there are ways to calculate in advance for many common cases as to how long each part will be if you specify it. Besides, I am not really sure if "print" even knows easily how many characters it is putting out as it chews away on the many things in your request and calls dunder methods in objects so they display themselves and so on. I assume it can be made to keep track, albeit I can imagine printing out an APL program with lots of overwritten characters where the number of bytes sent is way more than the number of spaces in the output. Why are we even still talking about this? The answer to the question of why print() does not return anything, let alone the number of characters printed, is BECAUSE. -Original Message- From: Python-list On Behalf Of Python Sent: Friday, February 10, 2023 4:56 PM To: python-list@python.org Subject: Re: evaluation question On Sat, Feb 11, 2023 at 08:30:22AM +1100, Chris Angelico wrote: > On Sat, 11 Feb 2023 at 07:36, Python wrote: > > You would do this instead: > > > > message = f"{username} has the occupation {job}." > > message_length = len(message) > > print(message) > > print(message_length) > > ... > > > > It's worth noting WHY output functions often return a byte count. It's > primarily for use with nonblocking I/O, with something like this:
Re: evaluation question
“Why are we even still talking about this?” Because humans are social creatures and some contributors to the list like to discuss things in depth. From: Python-list on behalf of avi.e.gr...@gmail.com Date: Friday, February 10, 2023 at 6:19 PM To: python-list@python.org Subject: RE: evaluation question *** Attention: This is an external email. Use caution responding, opening attachments or clicking on links. *** There are no doubt many situations someone wants to know how long something will be when printed but often at lower levels. In variable-width fonts, for example, the number of characters does not really line up precisely with how many characters. Some encodings use a varying number of bytes and, again, the width of the output varies. So for people who want to make 2-D formatted output like tables, or who want to wrap lines longer than N characters, you more often let some deeper software accept your data and decide on formatting it internally and either print it at once, when done calculating, or in the case of some old-style terminals, use something like the curses package that may use escape sequences to update the screen more efficiently in various ways. If someone wants more control over what they print, rather than asking the print() function to return something that is mostly going to be ignored, they can do the things others have already suggested here. You can make your message parts in advance and measure their length or anything else before you print. Or make a wrapper that does something for you before calling print, perhaps only for common cases and then returns the length to you after printing. I wonder if the next request will be for print() to know what your output device is and other current settings so it return the width your text takes up in pixels in the current font/size ... I add a tidbit that many ways of printing allow you to specify the width you want something printed in such as you want a floating point value with so many digits after the decimal point in a zero or space padded field on the left. So there are ways to calculate in advance for many common cases as to how long each part will be if you specify it. Besides, I am not really sure if "print" even knows easily how many characters it is putting out as it chews away on the many things in your request and calls dunder methods in objects so they display themselves and so on. I assume it can be made to keep track, albeit I can imagine printing out an APL program with lots of overwritten characters where the number of bytes sent is way more than the number of spaces in the output. Why are we even still talking about this? The answer to the question of why print() does not return anything, let alone the number of characters printed, is BECAUSE. -Original Message- From: Python-list On Behalf Of Python Sent: Friday, February 10, 2023 4:56 PM To: python-list@python.org Subject: Re: evaluation question On Sat, Feb 11, 2023 at 08:30:22AM +1100, Chris Angelico wrote: > On Sat, 11 Feb 2023 at 07:36, Python wrote: > > You would do this instead: > > > > message = f"{username} has the occupation {job}." > > message_length = len(message) > > print(message) > > print(message_length) > > ... > > > > It's worth noting WHY output functions often return a byte count. It's > primarily for use with nonblocking I/O, with something like this: > > buffer = b".." > buffer = buffer[os.write(fd, buffer):] > > It's extremely important to be able to do this sort of thing, but not > with the print function, which has a quite different job. I would agree with this only partially. Your case applies to os.write(), which is essentially just a wrapper around the write() system call, which has that sort of property... though it applies also to I/O in blocking mode, particularly on network sockets, where the number of bytes you asked to write (or read) may not all have been transferred, necessitating trying in a loop. However, Python's print() function is more analogous to C's printf(), which returns the number of characters converted for an entirely different reason... It's precisely so that you'll know what the length of the string that was converted is. This is most useful with the *snprintf() variants where you're actually concerned about overrunning the buffer you've provided for the output string, so you can realloc() the buffer if it was indeed too small, but it is also useful in the context of, say, a routine to format text according to the size of your terminal. In that context it really has nothing to do with blocking I/O or socket behavior. -- https://urldefense.com/v3/__https://mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!nyKmKANNzMqWDt2IGH9-Vv63_bioBGOYeokJy5GupmZVZIelplk15rvc_5NNbt6afc9yukh8y5X5mZXDVgr_PhY$<h
Re: evaluation question
On Fri, Feb 10, 2023 at 05:48:53PM -0500, Thomas Passin wrote: > On 2/10/2023 4:55 PM, Python wrote: > > However, Python's print() function is more analogous to C's printf(), > > which returns the number of characters converted for an entirely > > different reason... It's precisely so that you'll know what the length > > of the string that was converted is. This is most useful with the > > *snprintf() variants where you're actually concerned about overrunning > > the buffer you've provided for the output string, so you can realloc() > > the buffer if it was indeed too small, but it is also useful in the > > context of, say, a routine to format text according to the size of > > your terminal. In that context it really has nothing to do with > > blocking I/O or socket behavior. > > But none of that applies to the Python print() function. There are no > buffers to overrun, no reason to know the length of the printed string, no > re-allocating of a buffer. Indeed. But the OP originally compared print to printf, and I was specifically addressing Chris' point about why I/O functions return the number of bytes written, which was relevant to, but maybe a bit of tangent to the original post. > I don't know why the print() function doesn't return anything You do though! :) You actually just explained why yourself... it's because it just doesn't need to. But FWIW, I wasn't addressing this point, because it had already been adequately covered in the thread. There's good reason why Python's print and C's printf work differently. In languages like C it makes sense that printf returns the length of the string. printf is the means of all three of: - formatting the string - counting its length - actually outputting the string to stdout (albeit indirectly). This sort of breaks the rule of, "do one thing, and do it well," but it does so in the name of efficiency. You might or might not want to actually know the length of the formatted string, depending on what you're doing with it. But the printf function basically needs to calculate it anyway so that it can tell the underlying system calls how many bytes to write (or tell stdio how many bytes it is adding to its buffers, or whatever), and then stuffing that length in a register to be returned to the caller is roughly free (it's probably using the register that it's going to return already to do the counting), and the caller can ignore it if it wants to. C aims to be as efficient as possible so this is a good strategy. Unlike C[*], since Python can already separate the formatting and length calculation from sending the data to stdout (I demonstrated how in my first post in the thread), it has no need for print to return the length. As I mentioned in my earlier post, if Python encounters an error condition it will raise an exception--which C can't do--so there's no reason to return a status either. What else would it return? Nothing else would really make sense. -=-=-=- * In C you could sprintf the string into a buffer, which would return its length, and then call printf on the buffer, but that would be much less efficient and a bit silly... UNLESS you actually needed to know the length of the string beforehand, e.g. to calculate where to put line breaks in a text justification routine, or something. -- https://mail.python.org/mailman/listinfo/python-list
RE: evaluation question
There are no doubt many situations someone wants to know how long something will be when printed but often at lower levels. In variable-width fonts, for example, the number of characters does not really line up precisely with how many characters. Some encodings use a varying number of bytes and, again, the width of the output varies. So for people who want to make 2-D formatted output like tables, or who want to wrap lines longer than N characters, you more often let some deeper software accept your data and decide on formatting it internally and either print it at once, when done calculating, or in the case of some old-style terminals, use something like the curses package that may use escape sequences to update the screen more efficiently in various ways. If someone wants more control over what they print, rather than asking the print() function to return something that is mostly going to be ignored, they can do the things others have already suggested here. You can make your message parts in advance and measure their length or anything else before you print. Or make a wrapper that does something for you before calling print, perhaps only for common cases and then returns the length to you after printing. I wonder if the next request will be for print() to know what your output device is and other current settings so it return the width your text takes up in pixels in the current font/size ... I add a tidbit that many ways of printing allow you to specify the width you want something printed in such as you want a floating point value with so many digits after the decimal point in a zero or space padded field on the left. So there are ways to calculate in advance for many common cases as to how long each part will be if you specify it. Besides, I am not really sure if "print" even knows easily how many characters it is putting out as it chews away on the many things in your request and calls dunder methods in objects so they display themselves and so on. I assume it can be made to keep track, albeit I can imagine printing out an APL program with lots of overwritten characters where the number of bytes sent is way more than the number of spaces in the output. Why are we even still talking about this? The answer to the question of why print() does not return anything, let alone the number of characters printed, is BECAUSE. -Original Message- From: Python-list On Behalf Of Python Sent: Friday, February 10, 2023 4:56 PM To: python-list@python.org Subject: Re: evaluation question On Sat, Feb 11, 2023 at 08:30:22AM +1100, Chris Angelico wrote: > On Sat, 11 Feb 2023 at 07:36, Python wrote: > > You would do this instead: > > > > message = f"{username} has the occupation {job}." > > message_length = len(message) > > print(message) > > print(message_length) > > ... > > > > It's worth noting WHY output functions often return a byte count. It's > primarily for use with nonblocking I/O, with something like this: > > buffer = b".." > buffer = buffer[os.write(fd, buffer):] > > It's extremely important to be able to do this sort of thing, but not > with the print function, which has a quite different job. I would agree with this only partially. Your case applies to os.write(), which is essentially just a wrapper around the write() system call, which has that sort of property... though it applies also to I/O in blocking mode, particularly on network sockets, where the number of bytes you asked to write (or read) may not all have been transferred, necessitating trying in a loop. However, Python's print() function is more analogous to C's printf(), which returns the number of characters converted for an entirely different reason... It's precisely so that you'll know what the length of the string that was converted is. This is most useful with the *snprintf() variants where you're actually concerned about overrunning the buffer you've provided for the output string, so you can realloc() the buffer if it was indeed too small, but it is also useful in the context of, say, a routine to format text according to the size of your terminal. In that context it really has nothing to do with blocking I/O or socket behavior. -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Sat, 11 Feb 2023 at 10:07, Thomas Passin wrote: > > On 2/10/2023 4:55 PM, Python wrote: > > However, Python's print() function is more analogous to C's printf(), > > which returns the number of characters converted for an entirely > > different reason... It's precisely so that you'll know what the length > > of the string that was converted is. This is most useful with the > > *snprintf() variants where you're actually concerned about overrunning > > the buffer you've provided for the output string, so you can realloc() > > the buffer if it was indeed too small, but it is also useful in the > > context of, say, a routine to format text according to the size of > > your terminal. In that context it really has nothing to do with > > blocking I/O or socket behavior. > > But none of that applies to the Python print() function. There are no > buffers to overrun, no reason to know the length of the printed string, > no re-allocating of a buffer. It's certainly possible that one might > want to know the actual physical length of a displayed string - perhaps > to display it on a graphic - but now we're getting into font metrics and > such things, and we'll be doing something more active than displaying on > a terminal via stdout. It's sometimes possible to have that go to stdout (maybe you want to do columnar text or something), but yeah, you'll generally do that by formatting first, then doing the measurement, then displaying. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 2/10/2023 4:55 PM, Python wrote: However, Python's print() function is more analogous to C's printf(), which returns the number of characters converted for an entirely different reason... It's precisely so that you'll know what the length of the string that was converted is. This is most useful with the *snprintf() variants where you're actually concerned about overrunning the buffer you've provided for the output string, so you can realloc() the buffer if it was indeed too small, but it is also useful in the context of, say, a routine to format text according to the size of your terminal. In that context it really has nothing to do with blocking I/O or socket behavior. But none of that applies to the Python print() function. There are no buffers to overrun, no reason to know the length of the printed string, no re-allocating of a buffer. It's certainly possible that one might want to know the actual physical length of a displayed string - perhaps to display it on a graphic - but now we're getting into font metrics and such things, and we'll be doing something more active than displaying on a terminal via stdout. I don't know why the print() function doesn't return anything, but I'm fine with it. I've never felt that I needed to know. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Sat, Feb 11, 2023 at 08:30:22AM +1100, Chris Angelico wrote: > On Sat, 11 Feb 2023 at 07:36, Python wrote: > > You would do this instead: > > > > message = f"{username} has the occupation {job}." > > message_length = len(message) > > print(message) > > print(message_length) > > ... > > > > It's worth noting WHY output functions often return a byte count. It's > primarily for use with nonblocking I/O, with something like this: > > buffer = b".." > buffer = buffer[os.write(fd, buffer):] > > It's extremely important to be able to do this sort of thing, but not > with the print function, which has a quite different job. I would agree with this only partially. Your case applies to os.write(), which is essentially just a wrapper around the write() system call, which has that sort of property... though it applies also to I/O in blocking mode, particularly on network sockets, where the number of bytes you asked to write (or read) may not all have been transferred, necessitating trying in a loop. However, Python's print() function is more analogous to C's printf(), which returns the number of characters converted for an entirely different reason... It's precisely so that you'll know what the length of the string that was converted is. This is most useful with the *snprintf() variants where you're actually concerned about overrunning the buffer you've provided for the output string, so you can realloc() the buffer if it was indeed too small, but it is also useful in the context of, say, a routine to format text according to the size of your terminal. In that context it really has nothing to do with blocking I/O or socket behavior. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Sat, 11 Feb 2023 at 07:36, Python wrote: > If it's the case that you simply want to know the length of the string > that will be printed, you can, rather than expecting the I/O function > to tell that to you, figure it out for yourself ahead of time, e.g. > instead of: > > username = "John Smith" > job = "Python programmer" > > # this doesn't work as desired > len = print(f"{username} has occupation {job}.") > print(len) > ... > > You would do this instead: > > message = f"{username} has the occupation {job}." > message_length = len(message) > print(message) > print(message_length) > ... > It's worth noting WHY output functions often return a byte count. It's primarily for use with nonblocking I/O, with something like this: buffer = b".." buffer = buffer[os.write(fd, buffer):] It's extremely important to be able to do this sort of thing, but not with the print function, which has a quite different job. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Mon, Jan 30, 2023 at 09:41:03AM -, mutt...@dastardlyhq.com wrote: > >Because print() returns nothing (i.e., the statement x is None is True). > > I don't understand this. What was the point of the upheaval of converting > the print command in python 2 into a function in python 3 if as a function > print() doesn't return anything useful? Surely even the length of the > formatted string as per C's sprintf() function would be helpful? Python is far from the only language that allows functions to return nothing explicit. Statically typed languages typically use the void keyword or something similar to indicate this, and dynamically typed languages often just don't explicitly return anything. [Some languages, like Perl, just implicitly return the value of the last expression, or something of the sort, but some do not.] In Pascal, in fact, there are two different types of subroutines to distinguish between those things: functions return a value, and procedures do not. Modern languages commonly don't provide this distinction because by and large it is unnecessary. Typically the reason NOT to return a value is that the function is designed to DO something, rather than to calculate some value. Examples might be updating the appearance of a UI widget, printing some information to the screen, or twiddling some bits in a register (i.e. in-place update of a value). They don't need to return anything because the "output" is whatever was done. In some languages it might be typical to return a status indicating success or failure, but in many languages this is unnecessary; status may be returned via a parameter provided for the purpose, or in many languages, success can be assumed, whereas failure will raise an exception. If it's the case that you simply want to know the length of the string that will be printed, you can, rather than expecting the I/O function to tell that to you, figure it out for yourself ahead of time, e.g. instead of: username = "John Smith" job = "Python programmer" # this doesn't work as desired len = print(f"{username} has occupation {job}.") print(len) ... You would do this instead: message = f"{username} has the occupation {job}." message_length = len(message) print(message) print(message_length) ... -- https://mail.python.org/mailman/listinfo/python-list
RE: evaluation question
Ok I understand Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows From: Rob Cliffe via Python-list<mailto:python-list@python.org> Sent: Tuesday, February 7, 2023 6:54 PM To: Chris Angelico<mailto:ros...@gmail.com>; python-list@python.org<mailto:python-list@python.org> Subject: Re: evaluation question On 07/02/2023 08:15, Chris Angelico wrote: > On Tue, 7 Feb 2023 at 18:49, Rob Cliffe via Python-list > wrote: >> >> >> On 02/02/2023 09:31, mutt...@dastardlyhq.com wrote: >>> On Wed, 1 Feb 2023 18:28:04 +0100 >>> "Peter J. Holzer" wrote: >>>> --b2nljkb3mdefsdhx >>>> Content-Type: text/plain; charset=us-ascii >>>> Content-Disposition: inline >>>> Content-Transfer-Encoding: quoted-printable >>>> >>>> On 2023-02-01 09:00:39 -, mutt...@dastardlyhq.com wrote: >>>>> Its not evolution, its revolution. Evolution retains old functionality. >>>> Tell a penguin that it can fly :-) >>> Yeah ok :) But the ancestors of penguins didn't wake up one morning, flap >>> their wings and fall out the tree, it happened gradually. Python2 syntax >>> could have been retained for X versions of 3 just as C++ keeps old stuff >>> until its eventually deprecated them removed. >> Yeah? So what would this do: >> print () >> In Python 2 this prints an empty tuple. >> In Python 3 this is a call to the print function with no arguments, >> which prints a blank line. >> You can't have it both ways. >> In any case, supporting two different syntaxes simultaneously would be >> messy and difficult to maintain. > There are two solutions to this. The most obvious is "from __future__ > import print_function", which gives you the full power and flexibility > of Py3 in anything back as far as 2.6; the other is to always pass a > single string argument to print: > > print("") > print("spam %d ham %d" % (spam, ham)) > > This will work in pretty much ANY version of Python [1] and doesn't > require any sort of per-module configuration. > > The idea that old syntax should be retained is only part of the story. > While it's definitely important to not break old code unnecessarily, > it is far more important to ensure that there's *some way* to write > code that works across multiple versions. That's what we have here: > even with the breaking changes, there was usually a way to make your > code run identically on multiple versions. Sometimes this means a > compatibility shim at the top, like "try: raw_input; except NameError: > raw_input = input", and sometimes it means following a discipline like > putting b"..." for all strings that need to be bytes. But there always > needs to be a way. > > ChrisA > > [1] This is the part where someone points out to me that it wouldn't > work in Python 1.3 or something You are quite right Chris, and indeed I have used both solutions in my own code to keep 2-3 compatibility. I was just pointing out that continuing to support Python 2 syntax in Python 3 was not an option. Best wishes Rob Cliffe -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 07/02/2023 08:15, Chris Angelico wrote: On Tue, 7 Feb 2023 at 18:49, Rob Cliffe via Python-list wrote: On 02/02/2023 09:31, mutt...@dastardlyhq.com wrote: On Wed, 1 Feb 2023 18:28:04 +0100 "Peter J. Holzer" wrote: --b2nljkb3mdefsdhx Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2023-02-01 09:00:39 -, mutt...@dastardlyhq.com wrote: Its not evolution, its revolution. Evolution retains old functionality. Tell a penguin that it can fly :-) Yeah ok :) But the ancestors of penguins didn't wake up one morning, flap their wings and fall out the tree, it happened gradually. Python2 syntax could have been retained for X versions of 3 just as C++ keeps old stuff until its eventually deprecated them removed. Yeah? So what would this do: print () In Python 2 this prints an empty tuple. In Python 3 this is a call to the print function with no arguments, which prints a blank line. You can't have it both ways. In any case, supporting two different syntaxes simultaneously would be messy and difficult to maintain. There are two solutions to this. The most obvious is "from __future__ import print_function", which gives you the full power and flexibility of Py3 in anything back as far as 2.6; the other is to always pass a single string argument to print: print("") print("spam %d ham %d" % (spam, ham)) This will work in pretty much ANY version of Python [1] and doesn't require any sort of per-module configuration. The idea that old syntax should be retained is only part of the story. While it's definitely important to not break old code unnecessarily, it is far more important to ensure that there's *some way* to write code that works across multiple versions. That's what we have here: even with the breaking changes, there was usually a way to make your code run identically on multiple versions. Sometimes this means a compatibility shim at the top, like "try: raw_input; except NameError: raw_input = input", and sometimes it means following a discipline like putting b"..." for all strings that need to be bytes. But there always needs to be a way. ChrisA [1] This is the part where someone points out to me that it wouldn't work in Python 1.3 or something You are quite right Chris, and indeed I have used both solutions in my own code to keep 2-3 compatibility. I was just pointing out that continuing to support Python 2 syntax in Python 3 was not an option. Best wishes Rob Cliffe -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Tue, 7 Feb 2023 at 18:49, Rob Cliffe via Python-list wrote: > > > > On 02/02/2023 09:31, mutt...@dastardlyhq.com wrote: > > On Wed, 1 Feb 2023 18:28:04 +0100 > > "Peter J. Holzer" wrote: > >> --b2nljkb3mdefsdhx > >> Content-Type: text/plain; charset=us-ascii > >> Content-Disposition: inline > >> Content-Transfer-Encoding: quoted-printable > >> > >> On 2023-02-01 09:00:39 -, mutt...@dastardlyhq.com wrote: > >>> Its not evolution, its revolution. Evolution retains old functionality. > >> Tell a penguin that it can fly :-) > > Yeah ok :) But the ancestors of penguins didn't wake up one morning, flap > > their wings and fall out the tree, it happened gradually. Python2 syntax > > could have been retained for X versions of 3 just as C++ keeps old stuff > > until its eventually deprecated them removed. > Yeah? So what would this do: > print () > In Python 2 this prints an empty tuple. > In Python 3 this is a call to the print function with no arguments, > which prints a blank line. > You can't have it both ways. > In any case, supporting two different syntaxes simultaneously would be > messy and difficult to maintain. There are two solutions to this. The most obvious is "from __future__ import print_function", which gives you the full power and flexibility of Py3 in anything back as far as 2.6; the other is to always pass a single string argument to print: print("") print("spam %d ham %d" % (spam, ham)) This will work in pretty much ANY version of Python [1] and doesn't require any sort of per-module configuration. The idea that old syntax should be retained is only part of the story. While it's definitely important to not break old code unnecessarily, it is far more important to ensure that there's *some way* to write code that works across multiple versions. That's what we have here: even with the breaking changes, there was usually a way to make your code run identically on multiple versions. Sometimes this means a compatibility shim at the top, like "try: raw_input; except NameError: raw_input = input", and sometimes it means following a discipline like putting b"..." for all strings that need to be bytes. But there always needs to be a way. ChrisA [1] This is the part where someone points out to me that it wouldn't work in Python 1.3 or something -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 02/02/2023 09:31, mutt...@dastardlyhq.com wrote: On Wed, 1 Feb 2023 18:28:04 +0100 "Peter J. Holzer" wrote: --b2nljkb3mdefsdhx Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2023-02-01 09:00:39 -, mutt...@dastardlyhq.com wrote: Its not evolution, its revolution. Evolution retains old functionality. Tell a penguin that it can fly :-) Yeah ok :) But the ancestors of penguins didn't wake up one morning, flap their wings and fall out the tree, it happened gradually. Python2 syntax could have been retained for X versions of 3 just as C++ keeps old stuff until its eventually deprecated them removed. Yeah? So what would this do: print () In Python 2 this prints an empty tuple. In Python 3 this is a call to the print function with no arguments, which prints a blank line. You can't have it both ways. In any case, supporting two different syntaxes simultaneously would be messy and difficult to maintain. Better a clean break, with Python 2 support continuing for a long time (as it was). Best wishes Rob Cliffe -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Thu, 2 Feb 2023 16:09:09 - (UTC), Muttley wrote: > What if its not a few scripts? What if its 10s of thousands of lines of > core production code? If the company it belongs to wants to add new > Python 3 features it can't just plug them into the code because it won't > run under Python 3, they have to do a full overhaul or even complete > rewrite and that costs a lot of time and money. Tell me about it... Esri is the 500 pound gorilla in the GIS industry. They haven't been secretive about their roadmap but the tools people have been using for almost 20 years are going, going, GONE. Part of that is their scripting language ArcPy moved to 3.8. It's a minor inconvenience for me to update some old scripts and to develop with 3 but a lot of firms have those thousands of lines of code they've developed over the years in ArcPy for GIS data manipulation. More painful for me is the C++ API is also gone. Legacy sites have a couple of more years before it's all over. That leaves me with a foot in both worlds. > Unfortunately a lot of people who've never worked in large institutions > with huge code bases don't understand this. I don't work in a large company but I deal with about 25 years of legacy code every day. The core functionality is good but the time and money is spent putting lipstick on a pig. Technical debt is an industry wide problem. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 3/02/23 5:09 am, mutt...@dastardlyhq.com wrote: What if its 10s of thousands of lines of core production code? If the company it belongs to wants to add new Python 3 features it can't just plug them into the code because it won't run under Python 3, they have to do a full overhaul or even complete rewrite and that costs a lot of time and money. A possible strategy in that case would have been to incrementally rewrite it in such a way that the code would run in both 2.7 and 3.x (various features were added to 2.7 to make that possible). When that point is reached, you can then switch to running it with Python 3 and start using the new features. Also, if you're a company whose business is totally reliant on some piece of code, it would be prudent to plan ahead and budget for rewriting or replacing it at some point. People seem to think that because code doesn't wear out like hardware, you don't have to budget for replacing it. But you can't expect third party software to be maintained forever -- particularly when, as with Python, the maintenance is mainly being done by *volunteers*. -- Greg -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
mutt...@dastardlyhq.com wrote: On Wed, 1 Feb 2023 18:28:04 +0100 "Peter J. Holzer" wrote: --b2nljkb3mdefsdhx Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2023-02-01 09:00:39 -, mutt...@dastardlyhq.com wrote: Its not evolution, its revolution. Evolution retains old functionality. Tell a penguin that it can fly :-) Yeah ok :) But the ancestors of penguins didn't wake up one morning, flap their wings and fall out the tree, it happened gradually. Python2 syntax could have been retained for X versions of 3 just as C++ keeps old stuff until its eventually deprecated them removed. Python 2 *was* retained for X versions of Python 3. From a quick check, Python 3.0 was released in December 2008 and Python 2 support ended in January 2020 - by which time Python 3 was up to 3.8 as ChrisA mentioned. That's about an 11 year transition period, which is hardly sudden! Python 3 *was* the point at which the features deprecated in Python 2 were removed. The problem is, a lot seemed to ignore Python 3 for the first 12 years and then suddenly panic because Python 2 support had ended. -- Mark. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Fri, 3 Feb 2023 at 04:48, wrote: > Yeah ok :) But the ancestors of penguins didn't wake up one morning, flap > their wings and fall out the tree, it happened gradually. Python2 syntax > could have been retained for X versions of 3 just as C++ keeps old stuff > until its eventually deprecated them removed. What, you mean Python 2.7 could have continued to be supported until Python 3.8 (yes, that's not a typo) was released? It was. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Thu, 2 Feb 2023 09:31:46 - (UTC), Muttley wrote: > Yeah ok But the ancestors of penguins didn't wake up one morning, flap > their wings and fall out the tree, it happened gradually. Python2 syntax > could have been retained for X versions of 3 just as C++ keeps old stuff > until its eventually deprecated them removed. Isn't that prolonging the agony? I had some 2.7 scripts I had to move to 3. It wasn't that painful and I learned the new syntax. Being lazy if they still worked I would have kept using 2.7 syntax until someday it really went away. MS did it big time with VB .NET. I'm sure there still are people maintaining and extending old-style VB until it ceases to work altogether. Then they'll be faced with the same learning curve most people suffered through 20 years ago. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Wed, 1 Feb 2023 18:28:04 +0100 "Peter J. Holzer" wrote: >--b2nljkb3mdefsdhx >Content-Type: text/plain; charset=us-ascii >Content-Disposition: inline >Content-Transfer-Encoding: quoted-printable > >On 2023-02-01 09:00:39 -, mutt...@dastardlyhq.com wrote: >> Its not evolution, its revolution. Evolution retains old functionality. > >Tell a penguin that it can fly :-) Yeah ok :) But the ancestors of penguins didn't wake up one morning, flap their wings and fall out the tree, it happened gradually. Python2 syntax could have been retained for X versions of 3 just as C++ keeps old stuff until its eventually deprecated them removed. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 1 Feb 2023 17:31:02 GMT, Stefan Ram wrote: > rbowman writes: >> Why does every language have to invent their own function to >>print to the console that is very similar but not the same as the rest >>of the herd? > > Why do there have to be different languages at all? https://homepages.cwi.nl/~steven/abc/programmers/introduction.html "Why ABC? The answer to the question 'Why a new language?' is the same as the answer to the question 'Why new computers?': because they can help you do the job better. With the choice between a language where it will take a week to write a program, and a language where it will take an afternoon, most people will choose the latter." That leads to the question of when Van Rossum was looking for a hobby project, why not extend ABC? Or Pike? https://pike.lysator.liu.se/about/history/ Then there is the question of how a new language becomes popular. When Matsumoto developed Ruby it was almost 4 years before there was any coherent English documentation. How did it get traction? How about Go? Thompson and Pike hate C++ (with cause) so they went back to C and reworked it. Then there is C++ itself, which was released before its time. There are many more obscure languages when someone saw a need. Then there are features the propagate like lambdas. Everyone came down with lambda envy and shoehorned them into the language one way or the other. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 2/1/23 12:46 PM, Grant Edwards wrote: C (the language) doesn't support Unicode at all. There are, however, libraries that can be used to deal with it. No, it does, but only optionally. provides functions that manipulate Unicode "Characters" The type char32_t will hold Unicode Code Points, and you can define string literals of that type with U"string" notation. -- Richard Damon -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 2/1/23 3:59 AM, mutt...@dastardlyhq.com wrote: On Wed, 1 Feb 2023 11:59:25 +1300 Greg Ewing wrote: On 31/01/23 10:24 pm, mutt...@dastardlyhq.com wrote: All languages have their ugly corners due to initial design mistakes and/or constraints. Eg: java with the special behaviour of its string class, C++ with "=0" pure virtual declaration. But they don't dump them and make all old code suddenly cease to execute. No, but it was decided that Python 3 would have to be backwards incompatible, mainly to sort out the Unicode mess. Given that, the opportunity was taken to clean up some other mistakes as well. Unicode is just a string of bytes. C supports it with a few extra library functions to get unicode length vs byte length and similar. Its really not that hard. Rewriting an entire language just to support that sounds a bit absurd to me but hey ho... No, Unicode is a string of 21 bit characters. UTF-8 is a representation that uses bytes, but isn't itself "Unicode". The key fact is that a "String" variable is indexed not by bytes of UTF-8 encoding, but by actual characters. Python3 will store a string as either a sequence of Bytes if the data is all Latin-1, as a sequence of 16-bit words if the data all fits on th BMP, and a sequence of 32 bit words if it has a value outside the BMP. -- Richard Damon -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Thu, 2 Feb 2023 at 04:26, wrote: > > Its not evolution, its revolution. Evolution retains old functionality. > By the way, I'd like to see your opinions on eternal retention of old functionality. Which of these features are you willing to put effort into supporting? 1) Long integer constants eg 1234L which are the long type rather than the int type 2) dict.has_key method, doing the same job as "key in dict" 3) The input() function, which automatically evals what was entered at the keyboard 4) `x` which does the same as repr(x) 5) "from module import *" inside a function Retaining old functionality is all well and good, but there are limits, especially when the old functionality is downright wrong (input vs raw_input). Before you complain about other people's decisions, find out how many hours of YOUR time you're willing to invest into a project. Or alternatively, how many dollars you would spend on it. Let's pretend that you can pay for as many core Python developers as you like for USD 150,000 a year each. (See job posting https://jobs.pyfound.org/apply/TwgMP1b4OV/Security-Developer-In-Residence for where I got that figure from.) How many are you personally willing to hire in order to have these features maintained? It's easy to whine. Much harder to actually do something about it. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Thu, 2 Feb 2023 at 04:29, wrote: > > On Wed, 1 Feb 2023 11:59:25 +1300 > Greg Ewing wrote: > >On 31/01/23 10:24 pm, mutt...@dastardlyhq.com wrote: > >> All languages have their ugly corners due to initial design mistakes and/or > >> constraints. Eg: java with the special behaviour of its string class, C++ > >> with "=0" pure virtual declaration. But they don't dump them and make all > >> old > > > >> code suddenly cease to execute. > > > >No, but it was decided that Python 3 would have to be backwards > >incompatible, mainly to sort out the Unicode mess. Given that, > >the opportunity was taken to clean up some other mistakes as well. > > Unicode is just a string of bytes. C supports it with a few extra library > functions to get unicode length vs byte length and similar. Its really > not that hard. Rewriting an entire language just to support that sounds a > bit absurd to me but hey ho... > No, Unicode is NOT a string of bytes. UTF-8 is a string of bytes, but Unicode is not. If you disagree with the way Python has been developed, you're welcome to fork Python 2.7 and make your own language (but not called Python). Meanwhile, the rest of us really appreciate the fact that Python supports Unicode properly, not just as "a string of bytes". Also, be sure to deal with the technical debt of refusing to ever remove any feature. I'm curious how many dev hours that costs you. Incidentally, the bytes->unicode transformation wasn't Python 3's biggest reason for being. See https://peps.python.org/pep-3100/ for details. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 2023-02-01, Peter J. Holzer wrote: > On 2023-02-01 09:00:39 -, mutt...@dastardlyhq.com wrote: >> Its not evolution, its revolution. Evolution retains old functionality. > > Tell a penguin that it can fly :-) Penguins can fly. They just do it underwater... -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 2023-02-01, mutt...@dastardlyhq.com wrote: > >>No, but it was decided that Python 3 would have to be backwards >>incompatible, mainly to sort out the Unicode mess. Given that, >>the opportunity was taken to clean up some other mistakes as well. > > Unicode is just a string of bytes. No it isn't. Certain _encodings_ of Unicode are strings of bytes (UTF-8, for example). > C supports it with a few extra library functions to get unicode > length vs byte length and similar. Its really not that > hard. It is, actually. C (the language) doesn't support Unicode at all. There are, however, libraries that can be used to deal with it. > Rewriting an entire language just to support that sounds a bit > absurd to me but hey ho... Feel free to maintain your own fork of 2.7 :) The 2.7->3 incompatibility that created the most work for me was bytes. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 2023-02-01 09:00:39 -, mutt...@dastardlyhq.com wrote: > Its not evolution, its revolution. Evolution retains old functionality. Tell a penguin that it can fly :-) hp -- _ | Peter J. Holzer| Story must make more sense than reality. |_|_) || | | | h...@hjp.at |-- Charles Stross, "Creative writing __/ | http://www.hjp.at/ | challenge!" signature.asc Description: PGP signature -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Wed, 1 Feb 2023 11:59:25 +1300 Greg Ewing wrote: >On 31/01/23 10:24 pm, mutt...@dastardlyhq.com wrote: >> All languages have their ugly corners due to initial design mistakes and/or >> constraints. Eg: java with the special behaviour of its string class, C++ >> with "=0" pure virtual declaration. But they don't dump them and make all old > >> code suddenly cease to execute. > >No, but it was decided that Python 3 would have to be backwards >incompatible, mainly to sort out the Unicode mess. Given that, >the opportunity was taken to clean up some other mistakes as well. Unicode is just a string of bytes. C supports it with a few extra library functions to get unicode length vs byte length and similar. Its really not that hard. Rewriting an entire language just to support that sounds a bit absurd to me but hey ho... -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Wed, 1 Feb 2023 08:56:40 - (UTC), Muttley wrote: > Why couldn't they just keep "print" and call the function , oh I dunno, > "printf" ? Why does every language have to invent their own function to print to the console that is very similar but not the same as the rest of the herd? -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Tue, 31 Jan 2023 21:00:53 + Mark Bourne wrote: >Greg Ewing wrote: >> On 30/01/23 10:41 pm, mutt...@dastardlyhq.com wrote: >>> What was the point of the upheaval of converting >>> the print command in python 2 into a function in python 3 if as a >>> function >>> print() doesn't return anything useful? >> >> It was made a function because there's no good reason for it >> to have special syntax in the language. > >I think I saw somewhere that making print a function also had something >to do with being able to add extra keyword arguments like sep and end. >The syntax for printing to a specific file already seemed a bit odd with >the print statement, and adding extra arguments would have made it even >more clunky (yeah, I know ">>" is similar to C++ streams, but it looks >out of place in Python). Why couldn't they just keep "print" and call the function , oh I dunno, "printf" ? :) -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Wed, 1 Feb 2023 13:17:33 +1300 dn wrote: >On 01/02/2023 11.59, Greg Ewing wrote: >> On 31/01/23 10:24 pm, mutt...@dastardlyhq.com wrote: >>> All languages have their ugly corners due to initial design mistakes >>> and/or >>> constraints. Eg: java with the special behaviour of its string class, C++ >>> with "=0" pure virtual declaration. But they don't dump them and make >>> all old >>> code suddenly cease to execute. >> >> No, but it was decided that Python 3 would have to be backwards >> incompatible, mainly to sort out the Unicode mess. Given that, >> the opportunity was taken to clean up some other mistakes as well. > >+1 >and the move to Unicode has opened-up the Python community beyond the >US, to embrace 'the world' - a proposition (still) not well-recognised >by (only) English-speakers/writers/readers. > > >Even though the proposition has a troll-bait smell to it:- > >1 nothing "ceased to execute" and Python 2 was maintained and developed >for quite some time and in-parallel to many Python 3 releases. MacOS only comes with python3 now. If you have a whole load of python2 code you want to run you now have to manually install python2 yourself. >2 the only constant in this business is 'change'. I'd rather cope with >an evolution in this language (which we know and love), than one day Its not evolution, its revolution. Evolution retains old functionality. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 2023-01-31, Greg Ewing wrote: > That's only one of the syntactic oddities of the old print > statement, thogh. There was also the >> thing, special treatment > of trailing commas, etc. In "old" Python I used to use the trailing comma extensively, but I could never get myself to use the >> thing. I don't know why, but it just felt wrong. -- Grant -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 1/02/23 1:17 pm, dn wrote: 1 nothing "ceased to execute" and Python 2 was maintained and developed for quite some time and in-parallel to many Python 3 releases. And a lot of effort was put into making the transition as easy as possible, e.g. 2to3, and the features added to 2.7 to make it easier to write code that would work in both versions. -- Greg -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 01/02/2023 11.59, Greg Ewing wrote: On 31/01/23 10:24 pm, mutt...@dastardlyhq.com wrote: All languages have their ugly corners due to initial design mistakes and/or constraints. Eg: java with the special behaviour of its string class, C++ with "=0" pure virtual declaration. But they don't dump them and make all old code suddenly cease to execute. No, but it was decided that Python 3 would have to be backwards incompatible, mainly to sort out the Unicode mess. Given that, the opportunity was taken to clean up some other mistakes as well. +1 and the move to Unicode has opened-up the Python community beyond the US, to embrace 'the world' - a proposition (still) not well-recognised by (only) English-speakers/writers/readers. Even though the proposition has a troll-bait smell to it:- 1 nothing "ceased to execute" and Python 2 was maintained and developed for quite some time and in-parallel to many Python 3 releases. 2 the only constant in this business is 'change'. I'd rather cope with an evolution in this language (which we know and love), than one day realise that it has become dated or inflexible, and have to learn a new, replacement, language! -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 1/31/2023 6:18 PM, Greg Ewing wrote: On 1/02/23 7:33 am, Stefan Ram wrote: Thomas Passin writes: Some people say it is a function now so that you can redefine it. Hmm, I didn't write these quotes. Maybe someone got confused by the depth of the nested replies in this thread. Easy enough to do. Well, that's one benefit, but I wouldn't say it's the main one. The point is really that you can do *anything* with it now that you can do with a regular function -- pass it as an argument, wrap it with another function, define your own function with a similar signature for duck-typing purposes, etc. It would still be possible to have a special syntax for the outermost expression of an expression statement that would allow one to omit the parentheses, That's only one of the syntactic oddities of the old print statement, thogh. There was also the >> thing, special treatment of trailing commas, etc. Also, introducing a paren-less call syntax would be a very big and controversial change that would be way out of proportion to the problem. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Wed, 1 Feb 2023 at 10:47, Greg Ewing wrote: > That's only one of the syntactic oddities of the old print > statement, thogh. There was also the >> thing, special treatment > of trailing commas, etc. "Soft space" (the trailing comma behaviour) was an incredibly complex wart. Glad it's gone. > Also, introducing a paren-less call syntax would be a very big > and controversial change that would be way out of proportion to > the problem. Oddly enough, that WAS actually proposed recently - by Guido himself - as a demonstration of the power of the new PEG parser: https://mail.python.org/archives/list/python-id...@python.org/thread/NCQX6ZIBREUTLS52VVG3DSZ43OEXJFTT/ (The mailing list archive messes up formatting a bit with REPL transcripts, thinking they're quoted text.) The general consensus was "allowing function calls without parens causes more issues than it solves", with plenty of examples from other programming languages to prove this - Ruby, while generally a decent language, shows a rather nasty wart with this particular feature (see "Ruby allows parens-less function calls" from Steven D'Aprano in that thread). I don't think it'll ever happen in Python, but it's nice to know that the parser is flexible enough. It means that other weird cases, where the intuitive expectation is different, can be better handled (see eg "with (x as y, a as b):" syntax). Having print as a function is WAY better than having it as a special case with lots of warts. And it's so much easier to add extra features to it; for instance, how would you add a "flush after printing" flag to Py2's print statement? With a function, it's easy - just print(..., flush=True). ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 1/02/23 7:33 am, Stefan Ram wrote: Thomas Passin writes: Some people say it is a function now so that you can redefine it. Well, that's one benefit, but I wouldn't say it's the main one. The point is really that you can do *anything* with it now that you can do with a regular function -- pass it as an argument, wrap it with another function, define your own function with a similar signature for duck-typing purposes, etc. It would still be possible to have a special syntax for the outermost expression of an expression statement that would allow one to omit the parentheses, That's only one of the syntactic oddities of the old print statement, thogh. There was also the >> thing, special treatment of trailing commas, etc. Also, introducing a paren-less call syntax would be a very big and controversial change that would be way out of proportion to the problem. -- Greg -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 31/01/23 10:24 pm, mutt...@dastardlyhq.com wrote: All languages have their ugly corners due to initial design mistakes and/or constraints. Eg: java with the special behaviour of its string class, C++ with "=0" pure virtual declaration. But they don't dump them and make all old code suddenly cease to execute. No, but it was decided that Python 3 would have to be backwards incompatible, mainly to sort out the Unicode mess. Given that, the opportunity was taken to clean up some other mistakes as well. -- Greg -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
import io def countprint(*args, **kwargs): capturekw = {k:v for k,v in kwargs.items() if k != 'file'} buffer = io.StringIO() capturekw['file'] = buffer print(*args,**kwargs) print(*args,**capturekw) return len(buffer.getvalue()) def boolprint(*args,active:bool, **kwargs): if active: print(*args,**kwargs) with open("text.txt",'w') as f: y = countprint(1, 3, 3, sep=',', end='\n\n',file=f) print(y) boolprint(3,4,5,sep='/',active=True) boolprint(7,11,active=False) From: Python-list on behalf of avi.e.gr...@gmail.com Date: Tuesday, January 31, 2023 at 3:01 PM To: 'Thomas Passin' , python-list@python.org Subject: RE: evaluation question *** Attention: This is an external email. Use caution responding, opening attachments or clicking on links. *** I think its has been discussed here that many functions are DELIBERATELY designed to return without returning anything. Earlier languages like Pascal had explicit ideas that a function that did not return a value was declared as a "procedure" but many other languages like python make no real differentiation. Some functions are designed for a sort of side-effect and often there is nothing much that needs to be returned or even can be. If a function prints a dozen items one at a time, should it return nothing, or a copy of the last item or somehow of all items? Generally nothing looks right. If you want to return something, fine. Do it explicitly. Similar arguments have been made about methods that do things like sort the contents of an object internally and then return nothing. Some would like the return to be the (now altered) object itself. You can emulate that by not sorting internally but instead sorted(object) returns a new object that has been sorted from the old one. So should or could print return anything? Other languages exist, like R, that do return (and often ignore) whatever print displayed elsewhere. This can be of use in many ways such as making it easier to print or store additional copies without recalculating. My preference might be to simply allow a local option at the end of a print statement such as print(..., return=True) or even a way to set a global option so all print statements can be turned on when you want. But is this pythonic? In particular, people who want to give type hints now can safely claim it returns None and would have to modify that so it can optionally return something like str or None. And, of course, once you change print() this way, someone else will want the number of characters (or perhaps bytes) returned instead. Much of this can be worked around by simply making your own customized print function which evaluates the arguments to make a string and then calls print, perhaps with the results pre-calculated, and returns what you wanted. That is not as easy as it sounds, though as print supports various arguments like sep= and end= and file= and flush= so a weird but doable idea is simply to substitute a temporary file for any file= argument and write the results to a temporary file or something in memory that emulates a file. You can then read that back in and return what you want after handling the original print statement with the original arguments, or perhaps just use your result to any actually specified file or the default. You can thus create something like what you want and leave the original print() command alone to do what it was designed to do. And, in general, people who want a copy of what they print, often use other python functionality to craft some or all parts of the text they want printed and only then call print() and thus already may have the ability to use the text afterwards. For many purposes, including efficiency, returning nothing makes good sense. But it is not really the only choice or the right choice and yet, if you want to use THIS language, it has to be accepted as the documented choice. -Original Message- From: Python-list On Behalf Of Thomas Passin Sent: Tuesday, January 31, 2023 1:16 PM To: python-list@python.org Subject: Re: evaluation question On 1/31/2023 4:24 AM, mutt...@dastardlyhq.com wrote: > On Tue, 31 Jan 2023 12:57:33 +1300 > Greg Ewing wrote: >> On 30/01/23 10:41 pm, mutt...@dastardlyhq.com wrote: >>> What was the point of the upheaval of converting the print command >>> in python 2 into a function in python 3 if as a function >>> print() doesn't return anything useful? >> >> It was made a function because there's no good reason for it to have >> special syntax in the language. > > All languages have their ugly corners due to initial design mistakes > and/or constraints. Eg: java with the special behaviour of its string > class, C++ with "=0" pure virtual declaration. But they don't dump > them and make all old code suddenly cease to execute. > > Pragmatism should always come before language pu
Re: evaluation question
Greg Ewing wrote: On 30/01/23 10:41 pm, mutt...@dastardlyhq.com wrote: What was the point of the upheaval of converting the print command in python 2 into a function in python 3 if as a function print() doesn't return anything useful? It was made a function because there's no good reason for it to have special syntax in the language. I think I saw somewhere that making print a function also had something to do with being able to add extra keyword arguments like sep and end. The syntax for printing to a specific file already seemed a bit odd with the print statement, and adding extra arguments would have made it even more clunky (yeah, I know ">>" is similar to C++ streams, but it looks out of place in Python). They couldn't fully make the change from print statement to print function without breaking backward compatibility for existing code. But there were other breaking changes being made in Python 3 anyway, so may as well sort print out while at it and have all the breaking changes at once. Functions don't need to return things to justify their existence, and in fact the usual convention is that functions whose purpose is to have an effect just return None. -- Mark. -- https://mail.python.org/mailman/listinfo/python-list
RE: evaluation question
I think its has been discussed here that many functions are DELIBERATELY designed to return without returning anything. Earlier languages like Pascal had explicit ideas that a function that did not return a value was declared as a "procedure" but many other languages like python make no real differentiation. Some functions are designed for a sort of side-effect and often there is nothing much that needs to be returned or even can be. If a function prints a dozen items one at a time, should it return nothing, or a copy of the last item or somehow of all items? Generally nothing looks right. If you want to return something, fine. Do it explicitly. Similar arguments have been made about methods that do things like sort the contents of an object internally and then return nothing. Some would like the return to be the (now altered) object itself. You can emulate that by not sorting internally but instead sorted(object) returns a new object that has been sorted from the old one. So should or could print return anything? Other languages exist, like R, that do return (and often ignore) whatever print displayed elsewhere. This can be of use in many ways such as making it easier to print or store additional copies without recalculating. My preference might be to simply allow a local option at the end of a print statement such as print(..., return=True) or even a way to set a global option so all print statements can be turned on when you want. But is this pythonic? In particular, people who want to give type hints now can safely claim it returns None and would have to modify that so it can optionally return something like str or None. And, of course, once you change print() this way, someone else will want the number of characters (or perhaps bytes) returned instead. Much of this can be worked around by simply making your own customized print function which evaluates the arguments to make a string and then calls print, perhaps with the results pre-calculated, and returns what you wanted. That is not as easy as it sounds, though as print supports various arguments like sep= and end= and file= and flush= so a weird but doable idea is simply to substitute a temporary file for any file= argument and write the results to a temporary file or something in memory that emulates a file. You can then read that back in and return what you want after handling the original print statement with the original arguments, or perhaps just use your result to any actually specified file or the default. You can thus create something like what you want and leave the original print() command alone to do what it was designed to do. And, in general, people who want a copy of what they print, often use other python functionality to craft some or all parts of the text they want printed and only then call print() and thus already may have the ability to use the text afterwards. For many purposes, including efficiency, returning nothing makes good sense. But it is not really the only choice or the right choice and yet, if you want to use THIS language, it has to be accepted as the documented choice. -Original Message- From: Python-list On Behalf Of Thomas Passin Sent: Tuesday, January 31, 2023 1:16 PM To: python-list@python.org Subject: Re: evaluation question On 1/31/2023 4:24 AM, mutt...@dastardlyhq.com wrote: > On Tue, 31 Jan 2023 12:57:33 +1300 > Greg Ewing wrote: >> On 30/01/23 10:41 pm, mutt...@dastardlyhq.com wrote: >>> What was the point of the upheaval of converting the print command >>> in python 2 into a function in python 3 if as a function >>> print() doesn't return anything useful? >> >> It was made a function because there's no good reason for it to have >> special syntax in the language. > > All languages have their ugly corners due to initial design mistakes > and/or constraints. Eg: java with the special behaviour of its string > class, C++ with "=0" pure virtual declaration. But they don't dump > them and make all old code suddenly cease to execute. > > Pragmatism should always come before language purity. > It was more fundamental than that, and not mainly about print(): https://snarky.ca/why-python-3-exists/ -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 1/31/2023 4:24 AM, mutt...@dastardlyhq.com wrote: On Tue, 31 Jan 2023 12:57:33 +1300 Greg Ewing wrote: On 30/01/23 10:41 pm, mutt...@dastardlyhq.com wrote: What was the point of the upheaval of converting the print command in python 2 into a function in python 3 if as a function print() doesn't return anything useful? It was made a function because there's no good reason for it to have special syntax in the language. All languages have their ugly corners due to initial design mistakes and/or constraints. Eg: java with the special behaviour of its string class, C++ with "=0" pure virtual declaration. But they don't dump them and make all old code suddenly cease to execute. Pragmatism should always come before language purity. It was more fundamental than that, and not mainly about print(): https://snarky.ca/why-python-3-exists/ -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Tue, 31 Jan 2023 12:57:33 +1300 Greg Ewing wrote: >On 30/01/23 10:41 pm, mutt...@dastardlyhq.com wrote: >> What was the point of the upheaval of converting >> the print command in python 2 into a function in python 3 if as a function >> print() doesn't return anything useful? > >It was made a function because there's no good reason for it >to have special syntax in the language. All languages have their ugly corners due to initial design mistakes and/or constraints. Eg: java with the special behaviour of its string class, C++ with "=0" pure virtual declaration. But they don't dump them and make all old code suddenly cease to execute. Pragmatism should always come before language purity. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 30/01/23 10:41 pm, mutt...@dastardlyhq.com wrote: What was the point of the upheaval of converting the print command in python 2 into a function in python 3 if as a function print() doesn't return anything useful? It was made a function because there's no good reason for it to have special syntax in the language. Functions don't need to return things to justify their existence, and in fact the usual convention is that functions whose purpose is to have an effect just return None. -- Greg -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 30/01/2023 09:41, mutt...@dastardlyhq.com wrote: On Sun, 29 Jan 2023 23:57:51 -0500 Thomas Passin wrote: On 1/29/2023 4:15 PM, elvis-85...@notatla.org.uk wrote: On 2023-01-28, Louis Krupp wrote: On 1/27/2023 9:37 AM, mutt...@dastardlyhq.com wrote: eval("print(123)") 123 Does OP expect the text to come from the eval or from the print? x = print( [i for i in range(1, 10)] ) [1, 2, 3, 4, 5, 6, 7, 8, 9] x (nothing printed) Because print() returns nothing (i.e., the statement x is None is True). I don't understand this. What was the point of the upheaval of converting the print command in python 2 into a function in python 3 if as a function print() doesn't return anything useful? Surely even the length of the formatted string as per C's sprintf() function would be helpful? That's a fair question, or rather 2 fair questions. There is an explanation of why the change was made at https://snarky.ca/why-print-became-a-function-in-python-3/ In brief: (a) the print() function is more flexible and can be used in expressions (b) Python's syntax was simplified by dropping the special syntax used by the print statement. sys.stdout.write() does return the number of characters output (you could use this instead of print() if you need this; remember to add a '\n' character at the end of a line). I guess the option of making print() do the same either was not considered, or was rejected, when print was made a function. Best wishes Rob Cliffe -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Sun, 29 Jan 2023 23:57:51 -0500 Thomas Passin wrote: >On 1/29/2023 4:15 PM, elvis-85...@notatla.org.uk wrote: >> On 2023-01-28, Louis Krupp wrote: >>> On 1/27/2023 9:37 AM, mutt...@dastardlyhq.com wrote: >> >> >>> eval("print(123)") 123 >> >> >> Does OP expect the text to come from the eval or from the print? >> > x = print( [i for i in range(1, 10)] ) >> [1, 2, 3, 4, 5, 6, 7, 8, 9] >> > x >> (nothing printed) > >Because print() returns nothing (i.e., the statement x is None is True). I don't understand this. What was the point of the upheaval of converting the print command in python 2 into a function in python 3 if as a function print() doesn't return anything useful? Surely even the length of the formatted string as per C's sprintf() function would be helpful? -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 1/29/2023 4:15 PM, elvis-85...@notatla.org.uk wrote: On 2023-01-28, Louis Krupp wrote: On 1/27/2023 9:37 AM, mutt...@dastardlyhq.com wrote: eval("print(123)") 123 Does OP expect the text to come from the eval or from the print? x = print( [i for i in range(1, 10)] ) [1, 2, 3, 4, 5, 6, 7, 8, 9] x (nothing printed) Because print() returns nothing (i.e., the statement x is None is True). Other common constructs that return nothing are append(), sort(), and add(). It can be easy to forget this and write l2 = l1.sort() # l2 == None OTOH, you can (by slightly abusing the lambda) use this behavior to make a lambda expression print what it's receiving: >>> y = lambda x: print(f'Got {x}') or x**2 >>> z = y(3) Got 3 >>> z 9 >>> -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
mutt...@dastardlyhq.com wrote: On Sat, 28 Jan 2023 14:22:01 +1300 dn wrote: Do you know about the Python REPL? Haven't learnt the acronyms yet. REPL stands for "Read Evaluate Print Loop". It basically refers to the interactive interpreter, which reads input you type, evaluates it, prints the result, and loops (repeatedly does that). An interesting point from your examples is that the output from the first two comes from different steps in that loop. >>> eval("1+1") 2 Here, the E (evaluation) step runs eval("1+1"), which returns 2. The P (print) step then prints that result. If this was in a script, you wouldn't see any output, and the statement is pretty much useless - you'd need to assign the result to a variable or explicitly print it. >>> eval("print(123)") 123 Here, the E step runs eval("print(123)"), which prints 123 and returns None. The P step doesn't print anything if the result is None. You'd still see that output if this was in a script. Using eval in those examples is pretty pointless, since: >>> 1+1 >>> print(123) would produce the same results - but of course they were just simple examples. -- Mark. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 1/27/2023 9:37 AM, mutt...@dastardlyhq.com wrote: Hi This is probably a dumb newbie question but I've just started to learn python3 and eval() isn't behaving as I'd expect in that it works for some things and not others. eg: eval("1+1") 2 eval("print(123)") 123 eval("for i in range(1,10): i") Traceback (most recent call last): File "", line 1, in File "", line 1 for i in range(1,10): i ^ SyntaxError: invalid syntax Why did the 3rd one fail? Does it not handle complex expressions? Thanks for any help This might -- or might not -- be useful: eval( "print( [i for i in range(1, 10)] )" ) It prints a list, but you probably knew that: [1, 2, 3, 4, 5, 6, 7, 8, 9] Louis -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Sat, 28 Jan 2023 14:22:01 +1300 dn wrote: >On 28/01/2023 05.37, mutt...@dastardlyhq.com wrote: >> This is probably a dumb newbie question but I've just started to learn >> python3 and eval() isn't behaving as I'd expect in that it works for >> some things and not others. eg: >> > eval("1+1") >> 2 > eval("print(123)") >> 123 > eval("for i in range(1,10): i") >> Traceback (most recent call last): >>File "", line 1, in >>File "", line 1 >> for i in range(1,10): i >>^ >> SyntaxError: invalid syntax >> >> Why did the 3rd one fail? Does it not handle complex expressions? > >eval() is very powerful, and therefore rather dangerous in the risks it >presents. > >Thus, seems a strange/advanced question for a "newbie" to be asking. YMMV! Well ok, new-ish :) >Do you know about the Python REPL? Haven't learnt the acronyms yet. >If you open python within a terminal, each of the three >expressions/compound-statements listed will work, as desired, without >eval(). Umm, yeah, thats kind of obvious isn't it? -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Fri, 27 Jan 2023 21:04:58 + Ben Bacarisse wrote: >mutt...@dastardlyhq.com writes: > >> Hi > >It looks like you posted this question via Usenet. comp.lang.python is >essentially dead as a Usenet group. It exists, and gets NNTP versions >of mail sent to the mailing list, but nothing posted to the group via >NNTP get send on the mailing list. I prefer Usenet and dislike mailing >lists but that just means I can't really contribute to this "group" > >The "python-list" an an excellent resource (if you like the email >interface) and you can subscribe here: > >https://mail.python.org/mailman/listinfo/python-list>, > >> This is probably a dumb newbie question but I've just started to learn >> python3 and eval() isn't behaving as I'd expect in that it works for >> some things and not others. eg: >> > eval("1+1") >> 2 > eval("print(123)") >> 123 > eval("for i in range(1,10): i") >> Traceback (most recent call last): >> File "", line 1, in >> File "", line 1 >> for i in range(1,10): i >> ^ >> SyntaxError: invalid syntax >> >> Why did the 3rd one fail? Does it not handle complex expressions? > >It handles only expressions, and "for i in range(1,10): i" is not an >expression. You can use > exec("for i in range(1,10): i") Ok, thanks. -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On 28/01/2023 05.37, mutt...@dastardlyhq.com wrote: This is probably a dumb newbie question but I've just started to learn python3 and eval() isn't behaving as I'd expect in that it works for some things and not others. eg: eval("1+1") 2 eval("print(123)") 123 eval("for i in range(1,10): i") Traceback (most recent call last): File "", line 1, in File "", line 1 for i in range(1,10): i ^ SyntaxError: invalid syntax Why did the 3rd one fail? Does it not handle complex expressions? eval() is very powerful, and therefore rather dangerous in the risks it presents. Thus, seems a strange/advanced question for a "newbie" to be asking. YMMV! Do you know about the Python REPL? If you open python within a terminal, each of the three expressions/compound-statements listed will work, as desired, without eval(). dn $ ... python Python 3.11.1 (main, Jan 6 2023, 00:00:00) [GCC 12.2.1 20221121 (Red Hat 12.2.1-4)] on linux Type "help", "copyright", "credits" or "license" for more information. >>> 1+1 2 >>> print( 123 ) 123 >>> for i in range( 1, 10 ): i ... 1 2 3 4 5 6 7 8 9 >>> exit() -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
On Sat, 28 Jan 2023 at 11:45, wrote: > > Hi > > This is probably a dumb newbie question but I've just started to learn > python3 and eval() isn't behaving as I'd expect in that it works for > some things and not others. eg: > > >>> eval("1+1") > 2 > >>> eval("print(123)") > 123 > >>> eval("for i in range(1,10): i") > Traceback (most recent call last): > File "", line 1, in > File "", line 1 > for i in range(1,10): i > ^ > SyntaxError: invalid syntax > > Why did the 3rd one fail? Does it not handle complex expressions? > There's a difference between *expressions* (which have values) and *statements* (which do stuff, including control flow like loops). You may want the exec function instead. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: evaluation question
mutt...@dastardlyhq.com writes: > Hi It looks like you posted this question via Usenet. comp.lang.python is essentially dead as a Usenet group. It exists, and gets NNTP versions of mail sent to the mailing list, but nothing posted to the group via NNTP get send on the mailing list. I prefer Usenet and dislike mailing lists but that just means I can't really contribute to this "group" The "python-list" an an excellent resource (if you like the email interface) and you can subscribe here: https://mail.python.org/mailman/listinfo/python-list>, > This is probably a dumb newbie question but I've just started to learn > python3 and eval() isn't behaving as I'd expect in that it works for > some things and not others. eg: > eval("1+1") > 2 eval("print(123)") > 123 eval("for i in range(1,10): i") > Traceback (most recent call last): > File "", line 1, in > File "", line 1 > for i in range(1,10): i > ^ > SyntaxError: invalid syntax > > Why did the 3rd one fail? Does it not handle complex expressions? It handles only expressions, and "for i in range(1,10): i" is not an expression. You can use >>> exec("for i in range(1,10): i") or, to confirm that something is happening: >>> exec("for i in range(1,10): print(i)") 1 2 3 4 5 6 7 8 9 See: https://docs.python.org/3/library/functions.html?highlight=eval#eval and the immediately following entry. -- Ben. -- https://mail.python.org/mailman/listinfo/python-list