Re: Is using range() in for loops really Pythonic?
Your point about for-loops was applicable not only to Python, but to many other programming languages. So in response, I've added two new for-loop variations to Flaming Thunder. The two new variations are for-forever-do and for-expression-times-do. For-forever allows you to explicitly create infinite loops, and for- expression-times allows you to do something a specific number of times without having to declare a looping variable if you don't need one. Examples: Write Fa. For 8 times do write -la. For forever do ( Write Do you know the definition of insanity? . Read response. ). On May 10, 8:19 pm, John Salerno [EMAIL PROTECTED] wrote: I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times isunPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
George Sakkis wrote: If you push this logic too far, you should del every name immediately after the last statement it is used in the scope. I would generally find less readable some code spread with del every few lines, micro- managing the effective scope of each name. YMMV. Yes, but ... how about for i in range(10): del i do stuff ? It makes it clear you aren't using the index and ensures you get a run-time error if you clobbered an existing variable. Graham -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On Tue, 13 May 2008 10:20:41 -0700, John Nagle wrote: Matt Nordhoff wrote: Well, you should use xrange(10) instead of range(10). CPython really is naive. That sort of thing should be a compile-time optimization. It's not naive, it can't know at compile time what object is bound to the name `xrange` at runtime. Ciao, Marc 'BlackJack' Rintsch -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 14, 8:37 am, Marc 'BlackJack' Rintsch [EMAIL PROTECTED] wrote: On Tue, 13 May 2008 10:20:41 -0700, John Nagle wrote: Matt Nordhoff wrote: Well, you should use xrange(10) instead of range(10). CPython really is naive. That sort of thing should be a compile-time optimization. It's not naive, it can't know at compile time what object is bound to the name `xrange` at runtime. Ciao, Marc 'BlackJack' Rintsch I think he meant you should just use xrange over range at all times. -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] | The reason I even brought this up is because I remember someone saying a | while back (probably here on the newsgroup) that the true use of a for | loop was to iterate through a sequence (for the purpose of using that | sequence), not to do something X number of times. I believe the specific context was to counteract some people's tendency to write for i in range(len(seq)): do stuff with seq[i] when they would better (more Pythonically) write for item in seq: do stuff with item or even for i,item in enumerate(seq): do stuff with i and item. One subtle but real advantage is that the latter two forms work with iterables that do not have a known-ahead length or which even continue indefinitely. | Once they made this | comment, I suddenly saw the for loop in a new (and I believe purer) | light. That was the first time I realized what it was really meant | to do. That is an important insight. But to me it does not negate the do something n times usage when there is no iterable other than range to iterate. Do note that range has *not* been removed from 3.0 and that its main intended usage is for looping. | Now, you could easily make the argument that the Python for loop is a | much simpler tool to accomplish *both* of the above, and I suppose that | makes sense. Yes. Python leans toward minimalism. Proposals for various special-purpose loopin constructs have been rejected. For-loops cover most looping needs; while-loops cover everything else. Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On Mon, 12 May 2008 11:23:07 -0700, Carl Banks wrote: On May 12, 3:42 am, Ben Finney [EMAIL PROTECTED] wrote: Because of the precedent of those names, choosing one of those names doesn't make it clear to the reader that the value is never used; Why is it even necessary to document this? This is the thing that baffles me the most about this thread. I do it (with a special name) because static source checkers issue a warning for unused variables. Ciao, Marc 'BlackJack' Rintsch -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
REXX's loop construct subsumes all the common uses... And worse, it appears that a repetition and a condition can be part of the single statement. Thank you for pointing out the REXX examples. I am a Kedit user, but had forgotten about the REXX do-loops. I'll keep them in mind when I add an easy way to do this n times to Flaming Thunder this weekend. On May 11, 8:53 pm, Dennis Lee Bieber [EMAIL PROTECTED] wrote: On Mon, 12 May 2008 00:43:08 GMT, Jonathsn Cronin [EMAIL PROTECTED] declaimed the following in comp.lang.python: I agree in principle; the first is iteration and the second is repetition. In Python, the common idiom for a fixed number of repetitions is iterating over a number range. This is true in most languages I am familiar with, probably because fixed repetition, where you don't care about the index value, is rarely used. The only language I've used that does have fixed repetition is an (old) dialect of lisp, and I'm not sure it even made it into Common Lisp. Smalltalk and Ruby do have fixed repetition. REXX's loop construct subsumes all the common uses... And worse, it appears that a repetition and a condition can be part of the single statement. DO FOREVER ... END DO repeatcount ... END DO loopvar=first TO last BY step FOR reptcount ... END (where TO last, BY step, FOR reptcount are all optional clauses!) DO WHILE conditional ... END DO UNTIL conditional ... END Mixing modes DO loopvar=first BY step UNTIL conditional ... END Hmmm, looks like it's been extended for container objects (those that support MAKEARRAY): DO item OVER container ... END -- Wulfraed Dennis Lee Bieber KD6MOG [EMAIL PROTECTED] [EMAIL PROTECTED] HTTP://wlfraed.home.netcom.com/ (Bestiaria Support Staff: [EMAIL PROTECTED]) HTTP://www.bestiaria.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno wrote: I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? I use it quite often, especially if I want to implement a fixed number of retries on a communications channel. -Larry -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 13, 11:01 am, John Salerno [EMAIL PROTECTED] wrote:
Ben Finney wrote:
I think that the idiom
for unused in xrange(10):
# do stuff with no reference to 'unused'
is quite common. Is that what you're asking about?
Yes. I was more or less asking about the specific situation of using a
for loop to do something X number of times, but I think the more
generalized problem that everyone is talking about -- using a counter
variable that is never referenced in the loop -- probably puts the point
I was trying to make in a better light.
The reason I even brought this up is because I remember someone saying a
while back (probably here on the newsgroup) that the true use of a for
loop was to iterate through a sequence (for the purpose of using that
sequence), not to do something X number of times. Once they made this
comment, I suddenly saw the for loop in a new (and I believe purer)
light. That was the first time I realized what it was really meant
to do.
Using something like:
for unused in xrange(10):
# do stuff 10 times
suddenly seemed to me like a hackish way to replace
for (int i=0; i10; i++) {
// do stuff 10 times;
}
Not that I think the above code (C#) looks all that elegant either. But
in C# there is a distinction between the above, and this:
foreach (int i in sequence)
// do something;
which is more closely related to the Python for loop.
Now, you could easily make the argument that the Python for loop is a
much simpler tool to accomplish *both* of the above, and I suppose that
makes sense. Seems a little silly to have two separate for loops to do
these things. I just wasn't sure if the counter version of the Python
for loop was considered slightly unpythonic.
What was unPythonic, I think, as most people would agree, is to use
for like this:
--
for i in xrange(len(lst)):
pass
--
In VB, my language before Python, I've never used For Each even for a
sequence (Array, in VB), it seems too messy back then. Now, with
Python that only allowed a foreach statement, I realized that I never
really needed a for i in range(10) at all. Most of the time the places
where I need to do that is where the code is just a test code that
loops a certain number of times (with randomized input data), almost
never (probably never) met that in a real program code. And even in
some of those cases, the variables are usually used too (as a test
argument to the function being tested) or for logging purpose.
On May 13, 8:25 pm, Larry Bates [EMAIL PROTECTED] wrote:
(snip)
I use it quite often, especially if I want to implement a fixed number of
retries on a communications channel.
-Larry
That still have semantic meaning: 'tries'. If it was me, I'll go to
the trouble of giving names, since I would use it for logging or
informational purpose ('first try' 'second try' 'third try' 'no more
try').
I've never really met a real do something n times case, where the
variable doesn't hold any semantic meaning that I don't want to use
and is not a test case.
For me, a _ (or any other dummy variable[1]) is good enough and it's
easy to change if later I realized that I actually need to use the
variable. I agree though, that i, j, k for unused name is a bad choice
because single letter names is in common usage in mathematics.
[1] PEP 8 is useless if a certain code base has other agreed
convention, as long as the name used for a unused name in certain code
base is consistent (and probably documented), it never becomes a
problem.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 13, 9:20 pm, Lie [EMAIL PROTECTED] wrote:
On May 13, 11:01 am, John Salerno [EMAIL PROTECTED] wrote:
Ben Finney wrote:
I think that the idiom
for unused in xrange(10):
# do stuff with no reference to 'unused'
is quite common. Is that what you're asking about?
Yes. I was more or less asking about the specific situation of using a
for loop to do something X number of times, but I think the more
generalized problem that everyone is talking about -- using a counter
variable that is never referenced in the loop -- probably puts the point
I was trying to make in a better light.
The reason I even brought this up is because I remember someone saying a
while back (probably here on the newsgroup) that the true use of a for
loop was to iterate through a sequence (for the purpose of using that
sequence), not to do something X number of times. Once they made this
comment, I suddenly saw the for loop in a new (and I believe purer)
light. That was the first time I realized what it was really meant
to do.
Using something like:
for unused in xrange(10):
# do stuff 10 times
suddenly seemed to me like a hackish way to replace
for (int i=0; i10; i++) {
// do stuff 10 times;
}
Not that I think the above code (C#) looks all that elegant either. But
in C# there is a distinction between the above, and this:
foreach (int i in sequence)
// do something;
which is more closely related to the Python for loop.
Now, you could easily make the argument that the Python for loop is a
much simpler tool to accomplish *both* of the above, and I suppose that
makes sense. Seems a little silly to have two separate for loops to do
these things. I just wasn't sure if the counter version of the Python
for loop was considered slightly unpythonic.
What was unPythonic, I think, as most people would agree, is to use
for like this:
--
for i in xrange(len(lst)):
pass
--
In VB, my language before Python, I've never used For Each even for a
sequence (Array, in VB), it seems too messy back then. Now, with
Python that only allowed a foreach statement, I realized that I never
really needed a for i in range(10) at all. Most of the time the places
where I need to do that is where the code is just a test code that
loops a certain number of times (with randomized input data), almost
never (probably never) met that in a real program code. And even in
some of those cases, the variables are usually used too (as a test
argument to the function being tested) or for logging purpose.
On May 13, 8:25 pm, Larry Bates [EMAIL PROTECTED] wrote:
(snip)
I use it quite often, especially if I want to implement a fixed number of
retries on a communications channel.
-Larry
That still have semantic meaning: 'tries'. If it was me, I'll go to
the trouble of giving names, since I would use it for logging or
informational purpose ('first try' 'second try' 'third try' 'no more
try').
I've never really met a real do something n times case, where the
variable doesn't hold any semantic meaning that I don't want to use
and is not a test case.
For me, a _ (or any other dummy variable[1]) is good enough and it's
easy to change if later I realized that I actually need to use the
variable. I agree though, that i, j, k for unused name is a bad choice
because single letter names is in common usage in mathematics.
[1] PEP 8 is useless if a certain code base has other agreed
convention, as long as the name used for a unused name in certain code
base is consistent (and probably documented), it never becomes a
problem.
On my last message, I'm tempted not to say: We need to have /dev/null
for Python though I proved to fail.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
Matt Nordhoff wrote: John Salerno wrote: I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? Well, you should use xrange(10) instead of range(10). CPython really is naive. That sort of thing should be a compile-time optimization. John Nagle -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Nagle [EMAIL PROTECTED] writes: Matt Nordhoff wrote: Well, you should use xrange(10) instead of range(10). CPython really is naive. That sort of thing should be a compile-time optimization. Or even a case of the 'xrange' behaviour making 'range' obsolete. Which, as I pointed out earlier in the thread, it is in Python 3.0. -- \ Yesterday I parked my car in a tow-away zone. When I came back | `\ the entire area was missing. -- Steven Wright | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
Ivan Illarionov [EMAIL PROTECTED] writes: In such cases, the name 'dummy' is conventionally bound to the items from the iterator, for clarity of purpose [..] If a value isn't used, then I think the most clear name for it is unused. [...] Maybe my brain works differently, but I find both dummy and unused are extremely confusing names for loop counters. The loop begins to look like it doesn't iterate at all if its counter is dummy or unused. If it *counts* it is *used* and it's *not* dummy. The value is unused by any of the code inside the block. For the purposes of that block, it is a dummy value. That something *else* (the iterator driving the 'for') is taking care of knowing when the loop is finished is great. However, in the code the programmer is writing, the loop counter is entirely unused. Why reinvent the wheel when a common identifier naming convention is for the loop counter to use the variable names i, j and k (and so on if needed) (from Wikipedia http://en.wikipedia.org/wiki/Loop_counter ) That is also regrettably common in Python code. It still suffers from being unnecessarily ambiguous, since there are *also* plenty of loops using 'i', 'j', etc. where the loop counter *is* used. Differentiating these use cases by appropriate naming is, IMO, worth the effort of choosing a meaningful name. -- \ Ignorance more frequently begets confidence than does | `\ knowledge. —Charles Darwin, _The Descent of Man_, 1871 | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 11, 9:28 pm, Arnaud Delobelle [EMAIL PROTECTED] wrote:
Hi John, Arnaud;
Contrived example:
# Print 'hello' 10 times; x is not used
for x in xrange(10):
print 'hello'
I've used Fortran and C and so would tend to use either i,j,k as the
unused loop variable above, or, for clarity, call it something
descriptive like loop_count, if the loop body would be clearer.
I would also just use range for small, (especially small constant),
ranges.
# By changing what is iterated over, no unused variable:
from itertools import repeat
for msg in repeat('hello', 10):
print msg
I guess I would not go to the trouble of using itertools.repeat unless
it was simplifying/homogenising a larger expression - i.e if it was
part of some functional expression
I've never fealt the need for a separate repeat statement myself
either.
- Paddy.
P.S: I do understand that your examples are contrived. Just my
thoughts.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On Mon, 12 May 2008 16:24:23 +1000, Ben Finney wrote: [...] That is also regrettably common in Python code. It still suffers from being unnecessarily ambiguous, since there are *also* plenty of loops using 'i', 'j', etc. where the loop counter *is* used. Differentiating these use cases by appropriate naming is, IMO, worth the effort of choosing a meaningful name. Even if the counter is not used inside the loop's body it's still in control of the whole loop and, IMO, any special discriminating and non- conventional name doesn't worth the added confusion. -- Ivan -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno schreef: Ben Finney wrote: John Salerno [EMAIL PROTECTED] writes: num = 33 for x in xrange(10): print num += 1 Which is better done by 'num += 10'. Can you come up with an example that isn't trivially replaced with clearer code? That might make it clearer what your concern is. ::sigh:: No, unfortunately I don't have a strong enough grasp of Python to give a really in-depth example. I understand what you're asking though. Perhaps people don't use this idiom as much as I think they do, so to give a trivial example to support my point isn't helpful. Perhaps a function to print some text a number of times: def print_n(text, n): for i in xrange(n): print text (Though I guess you can replace that with print '\n'.join(msg * n) ) -- The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom. -- Isaac Asimov Roel Schroeven -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
Ivan Illarionov [EMAIL PROTECTED] writes: On Mon, 12 May 2008 16:24:23 +1000, Ben Finney wrote: [...] That is also regrettably common in Python code. It still suffers from being unnecessarily ambiguous, since there are *also* plenty of loops using 'i', 'j', etc. where the loop counter *is* used. Differentiating these use cases by appropriate naming is, IMO, worth the effort of choosing a meaningful name. Even if the counter is not used inside the loop's body it's still in control of the whole loop Not in Python it's not. The values that come out of the iterator aren't in control of the loop. The state for the loop is in the *iterator*, not the values that come out. Having access to the values that come from the iterator is usually useful, but regardless of whether one uses them or not, they're *not* controlling the loop, and it's confusing to imply that they are. So, when not using the values that come from the controlling iterator, it's good to make that explicit. If Python supported it, we might prefer to use no name at all for something that isn't used, but the 'for' syntax doesn't allow that. In the absence of supporting syntax, the next best thing is to choose a name that *does* make it explicit that the values will not be used. -- \ “All television is educational television. The question is: | `\ what is it teaching?” —Nicholas Johnson | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
Paddy [EMAIL PROTECTED] writes: I've used Fortran and C and so would tend to use either i,j,k as the unused loop variable above, or, for clarity, call it something descriptive like loop_count, if the loop body would be clearer. The problem with all of these names is that they also have long precedent as names of values that *will* be used inside the loop. Because of the precedent of those names, choosing one of those names doesn't make it clear to the reader that the value is never used; they have no indication from you of that until they look over the code a few times. It's implicit rather than explicit. -- \ As I bit into the nectarine, it had a crisp juiciness about it | `\ that was very pleasurable - until I realized it wasn't a | _o__)nectarine at all, but A HUMAN HEAD!! -- Jack Handey | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On Mon, 12 May 2008 16:24:23 +1000, Ben Finney wrote: [...] That is also regrettably common in Python code. It still suffers from being unnecessarily ambiguous, since there are *also* plenty of loops using 'i', 'j', etc. where the loop counter *is* used. Differentiating these use cases by appropriate naming is, IMO, worth the effort of choosing a meaningful name. Even if the counter is not used inside the loop's body it's still in control of the whole loop Not in Python it's not. The values that come out of the iterator aren't in control of the loop. The state for the loop is in the *iterator*, not the values that come out. Having access to the values that come from the iterator is usually useful, but regardless of whether one uses them or not, they're *not* controlling the loop, and it's confusing to imply that they are. I agree that in control was incorrect phrase. So, when not using the values that come from the controlling iterator, it's good to make that explicit. If Python supported it, we might prefer to use no name at all for something that isn't used, but the 'for' syntax doesn't allow that. In the absence of supporting syntax, the next best thing is to choose a name that *does* make it explicit that the values will not be used. Name 'i' does not imply whether it's used inside the loop or not. IMO it perfectly covers both cases. It may have small advantage to make it explicit that the values will not be used, but names like dummy, unused, ignored or junk can be confusing for some people and break the established conventions for counter variable names (and these conventions are reasonable and are taken from mathematics). i is still the best choice. And let's agree to disagree. It's clear that we have different opinions and it looks that this discussion is not going to change them. -- Ivan -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On 2008-05-12, Ben Finney [EMAIL PROTECTED] wrote: Maybe my brain works differently, but I find both dummy and unused are extremely confusing names for loop counters. The loop begins to look like it doesn't iterate at all if its counter is dummy or unused. If it *counts* it is *used* and it's *not* dummy. The value is unused by any of the code inside the block. For the purposes of that block, it is a dummy value. The value may be unused, but for me it's the name that matters, not the value. The name might be in use by other code, and the careless choice of a dummy name that's _supposed_ to be unused has broken code precisely becuase the name was being used (for something else). Requiring that the user pollute a namespace with a useless name is a wart. That is also regrettably common in Python code. It still suffers from being unnecessarily ambiguous, since there are *also* plenty of loops using 'i', 'j', etc. where the loop counter *is* used. Perhaps I'm the only one who's ever been stupid enough to overwrite an index named i (that is being used) with another index named i (that isn't being used)... -- Grant Edwards grante Yow! All of life is a blur at of Republicans and meat! visi.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On 2008-05-12, Ben Finney [EMAIL PROTECTED] wrote: I too, agree that requiring a name be bound to the values coming out of the iterator seems wrong. With do something N times, there must be *something* to keep track of which iteration we're up to (or, equivalently, how many iterations remain) at a given moment. A Python iterator seems a fine choice to hold that information, and better than many alternatives. An iterator like xrange() is an excellent choice. But, since the iterator contains that information, why require that that value be exported by the iterator and bound to an externally visible name? In the case in question, the only thing you need from the iterator is the StopIteration exception. To me, exposing the internal state of the iterator and requiring that the user bind a name to it each time through the loop feels we're like driving a nail with a screwdriver. -- Grant Edwards grante Yow! Was my SOY LOAF left at out in th'RAIN? It tastes visi.comREAL GOOD!! -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On 2008-05-12, Ben Finney [EMAIL PROTECTED] wrote: Paddy [EMAIL PROTECTED] writes: I've used Fortran and C and so would tend to use either i,j,k as the unused loop variable above, or, for clarity, call it something descriptive like loop_count, if the loop body would be clearer. The problem with all of these names is that they also have long precedent as names of values that *will* be used inside the loop. I guess people who standardize on loop_count never nest loops. :) Because of the precedent of those names, choosing one of those names doesn't make it clear to the reader that the value is never used; they have no indication from you of that until they look over the code a few times. It's implicit rather than explicit. And when somebody adds a nested loop things fall apart. -- Grant Edwards grante Yow! BARBARA STANWYCK makes at me nervous!! visi.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 12, 3:46 pm, Grant Edwards [EMAIL PROTECTED] wrote: On 2008-05-12, Ben Finney [EMAIL PROTECTED] wrote: Paddy [EMAIL PROTECTED] writes: I've used Fortran and C and so would tend to use either i,j,k as the unused loop variable above, or, for clarity, call it something descriptive like loop_count, if the loop body would be clearer. The problem with all of these names is that they also have long precedent as names of values that *will* be used inside the loop. I guess people who standardize on loop_count never nest loops. :) Because of the precedent of those names, choosing one of those names doesn't make it clear to the reader that the value is never used; they have no indication from you of that until they look over the code a few times. It's implicit rather than explicit. And when somebody adds a nested loop things fall apart. I don't have an example to hand. A lot of casses of repeat_X_times inside a loop of repeat_Y_times would naturally be written as repeat_Y*X_times. Oh, wait a bit, oversimplified_example_alert for i in range(3): print Stay! for j in range(2): print Come over. /oversimplified_example_alert Which could become: for outer_stay_repetions in range(3): print Stay! for inner_come_over_repetions in range(2): print Come over. But the second is daft. Nested repeats don't neccessarily pose a problem to choosing meaningful names for repeat counters that are not going to be referenced in the loop body, and most times i,j,k are fine for used and un-used loop indices I find. - Paddy (Or were you just having a laugh ;-) -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 12, 3:42 am, Ben Finney [EMAIL PROTECTED] wrote: Because of the precedent of those names, choosing one of those names doesn't make it clear to the reader that the value is never used; Why is it even necessary to document this? This is the thing that baffles me the most about this thread. Think about all the various aspect of a varibale: * is it some common usage archetype * value it represents * scope * (expected) type * physical units of measure * software package it belongs to * whether it's used in the program or not * scalar, structure, or array * mutable or constant * and so on You cannot possibly document all of this pertinent information in the name alone. A variable's name is a very limited resource: one can only document a tiny number of things, so one must prioritize. IMHO, whether a varibale is used or not has got to be one of the least important things of all (in no small part because it's easily discernable from nearby code). In fact, I'd say it's so irrelevant I probably wouldn't have listed it if it wasn't the topic of discussion. The first two items I listed are the most important to me. If a variable fills the archetypal role of counter, then it ought to be named like a counter; this usually trumps all other concerns. (Never mind that the varibale here isn't really a counter, it still fills the archetypal role of one, which is more important. The name of a variable is for the reader's benefit.) So I would have to agree with Ivan Illarionov. Having said that, if you do think it's most important to document whether something is used, I would suggest not using _ (because it's conflicts with gettext conventions) or dummy (because it's misleading) for it. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
Carl Banks [EMAIL PROTECTED] writes: IMHO, whether a varibale is used or not has got to be one of the least important things of all (in no small part because it's easily discernable from nearby code). I couldn't disagree more. If you're binding a name to a value that will never be used, you're doing me (the reader of the code) a great favour if you indicate clearly and concisely that this value is not intended to be referenced anywhere else. Saving time for the reader is a very important job of the writer of code. Having said that, if you do think it's most important to document whether something is used, I would suggest not using _ (because it's conflicts with gettext conventions) or dummy (because it's misleading) for it. Agreed. Note, too, that the ideal answer to this is don't bind names at all to values that will never be used. It's only because the specifics of Python's 'for' statement require us to do this that we are discussing the ramifications of what to do when what Python requires of us is actually unnecessary for our purposes. -- \ Friendship is born at that moment when one person says to | `\ another, 'What! You too? I thought I was the only one!' -- | _o__) C.S. Lewis | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 12, 7:03 pm, Ben Finney [EMAIL PROTECTED] wrote: Carl Banks [EMAIL PROTECTED] writes: IMHO, whether a varibale is used or not has got to be one of the least important things of all (in no small part because it's easily discernable from nearby code). I couldn't disagree more. If you're binding a name to a value that will never be used, you're doing me (the reader of the code) a great favour if you indicate clearly and concisely that this value is not intended to be referenced anywhere else. Saving time for the reader is a very important job of the writer of code. I don't think knowing in advance whether a variable is going to be used or not benefits readability. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
Ben Finney [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] | So, when not using the values that come from the controlling iterator, | it's good to make that explicit. If Python supported it, we might | prefer to use no name at all for something that isn't used, but the | 'for' syntax doesn't allow that. But I presume it could if [target 'in'] were optional. for range(n): stuff to do n times It is possible this has been proposed and rejected, but I have no specific memory. tjr -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 10, 8:19 pm, John Salerno [EMAIL PROTECTED] wrote: It seems somewhat artificial to use the for loop to do something a certain number of times, like above. I agree; it's a common flaw with lots of languages, not just Python. I'd be inclined to use something like: FOR 8 TIMES DO statement. or: REPEAT statement FOR 8 TIMES. as a compromise between readability and machine-parsability. If anyone has other suggestions, please post them here and I'll implement one of them next weekend in Flaming Thunder. -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 12, 7:03 pm, Ben Finney [EMAIL PROTECTED] wrote: Carl Banks [EMAIL PROTECTED] writes: IMHO, whether a varibale is used or not has got to be one of the least important things of all (in no small part because it's easily discernable from nearby code). I couldn't disagree more. If you're binding a name to a value that will never be used, you're doing me (the reader of the code) a great favour if you indicate clearly and concisely that this value is not intended to be referenced anywhere else. Saving time for the reader is a very important job of the writer of code. If you push this logic too far, you should del every name immediately after the last statement it is used in the scope. I would generally find less readable some code spread with del every few lines, micro- managing the effective scope of each name. YMMV. George -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
Ben Finney wrote:
I think that the idiom
for unused in xrange(10):
# do stuff with no reference to 'unused'
is quite common. Is that what you're asking about?
Yes. I was more or less asking about the specific situation of using a
for loop to do something X number of times, but I think the more
generalized problem that everyone is talking about -- using a counter
variable that is never referenced in the loop -- probably puts the point
I was trying to make in a better light.
The reason I even brought this up is because I remember someone saying a
while back (probably here on the newsgroup) that the true use of a for
loop was to iterate through a sequence (for the purpose of using that
sequence), not to do something X number of times. Once they made this
comment, I suddenly saw the for loop in a new (and I believe purer)
light. That was the first time I realized what it was really meant
to do.
Using something like:
for unused in xrange(10):
# do stuff 10 times
suddenly seemed to me like a hackish way to replace
for (int i=0; i10; i++) {
// do stuff 10 times;
}
Not that I think the above code (C#) looks all that elegant either. But
in C# there is a distinction between the above, and this:
foreach (int i in sequence)
// do something;
which is more closely related to the Python for loop.
Now, you could easily make the argument that the Python for loop is a
much simpler tool to accomplish *both* of the above, and I suppose that
makes sense. Seems a little silly to have two separate for loops to do
these things. I just wasn't sure if the counter version of the Python
for loop was considered slightly unpythonic.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 11, 4:19 am, John Salerno [EMAIL PROTECTED] wrote: I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? The range() function returns a list and list is a sequence, isn't? -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 11, 12:38 am, Paul Rubin http://[EMAIL PROTECTED] wrote: John Salerno [EMAIL PROTECTED] writes: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. It is pretty natural in imperative-style code. The one thing I'd do differently is use xrange instead of range, to avoid creating a 10-element list in memory before starting the loop. If you give extras to memory, can Python live? -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
XLiIV [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] On May 11, 4:19 am, John Salerno [EMAIL PROTECTED] wrote: I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? |The range() function returns a list and list is a sequence, isn't? yes, for loops iterate thru any iterable -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno wrote: I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? Ok, I think most people are misunderstanding my question a little. I probably should have said xrange instead of range, but the point of my question remains the same: Should a for loop be used simply to do something X number of times, or should it strictly be used to step through an iterable object for the purpose of processing the items in that object? -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
XLiIV wrote: The range() function returns a list and list is a sequence, isn't? I think you're missing the point. To me, there seems to be a fundamental difference between these two things: --- people = ['Sam', 'Bob', 'Fred'] for name in people: print name --- AND --- num = 33 for x in xrange(10): print num += 1 --- To me, the first example is a pure use of the for loop. You are iterating through an object and *using* the items you are stepping through. The second example, however, is simply doing something 10 times, and what it's doing has nothing to do with 'x' or xrange. So it seems like an abuse of the for loop. -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno [EMAIL PROTECTED] writes:
John Salerno wrote:
I know it's popular and very handy, but I'm curious if there are purists
out there who think that using something like:
for x in range(10):
#do something 10 times
is unPythonic. The reason I ask is because the structure of the for loop
seems to be for iterating through a sequence. It seems somewhat
artificial to use the for loop to do something a certain number of
times, like above.
Anyone out there refuse to use it this way, or is it just impossible to
avoid?
Ok, I think most people are misunderstanding my question a little. I
probably should have said xrange instead of range, but the point of my
question remains the same:
Should a for loop be used simply to do something X number of times, or
should it strictly be used to step through an iterable object for the
purpose of processing the items in that object?
It makes me feel slightly uncomfortable too, but AFAIK there is no
better way in Python. What I sometimes do is make the for loop bind
its variable to something useful instead of an unused counter.
Contrived example:
# Print 'hello' 10 times; x is not used
for x in xrange(10):
print 'hello'
# By changing what is iterated over, no unused variable:
from itertools import repeat
for msg in repeat('hello', 10):
print msg
--
Arnaud
--
http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno [EMAIL PROTECTED] writes: num = 33 for x in xrange(10): print num += 1 Which is better done by 'num += 10'. Can you come up with an example that isn't trivially replaced with clearer code? That might make it clearer what your concern is. The [above] example [...] is simply doing something 10 times, and what it's doing has nothing to do with 'x' or xrange. So it seems like an abuse of the for loop. In such cases, the name 'dummy' is conventionally bound to the items from the iterator, for clarity of purpose:: for dummy in range(10): # do stuff that makes no reference to 'dummy' Also note that 'range' will return an iterator (not a list) in Python 3.0, and 'xrange' is removed since it's then obsolete URL:http://www.python.org/dev/peps/pep-3100/#built-in-namespace. -- \ “Isn’t it enough to see that a garden is beautiful without | `\ having to believe that there are fairies at the bottom of it | _o__) too?” —Douglas Adams | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno wrote: To me, the first example is a pure use of the for loop. You are iterating through an object and *using* the items you are stepping through. The second example, however, is simply doing something 10 times, and what it's doing has nothing to do with 'x' or xrange. So it seems like an abuse of the for loop. Well, I would say this: myl = ['a', 'b', 'c', 'd'] for i in xrange(len(myl)): print myl[i] As you would see in other languages, is an abuse in python. But in you need to iterate 5 times over something. Do you have a cleaner / python'er alternative ? Do you find the following cleaner: x = 0 while x = 4: print x x += 1 Yves. http://www.SollerS.ca -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On Sun, 11 May 2008 16:16:53 -0400, John Salerno wrote (in message [EMAIL PROTECTED]): XLiIV wrote: The range() function returns a list and list is a sequence, isn't? I think you're missing the point. To me, there seems to be a fundamental difference between these two things: --- people = ['Sam', 'Bob', 'Fred'] for name in people: print name --- AND --- num = 33 for x in xrange(10): print num += 1 --- To me, the first example is a pure use of the for loop. You are iterating through an object and *using* the items you are stepping through. The second example, however, is simply doing something 10 times, and what it's doing has nothing to do with 'x' or xrange. So it seems like an abuse of the for loop. I agree in principle; the first is iteration and the second is repetition. In Python, the common idiom for a fixed number of repetitions is iterating over a number range. This is true in most languages I am familiar with, probably because fixed repetition, where you don't care about the index value, is rarely used. The only language I've used that does have fixed repetition is an (old) dialect of lisp, and I'm not sure it even made it into Common Lisp. Smalltalk and Ruby do have fixed repetition. Using range may not be entirely elegant, but is pragmatic, and not, to me, particularly ugly. In Python, unlike some languages, you don't have to declare the x. I think you could add it without too much change to the parsing. for expression: block Seeing a : instead of in would mean a repetition statement which would be interpreted as: -- if expression evaluates to an integer, execute the block that number of times. -- If expression evaluates to an iterator, execute the block until the iterator is exhausted. Even if possible, I see this at best a minor improvement and more likely a negative because the for keyword is now overloaded. (see static in C/Java.) You could add a new keyword but the benefit here is much to small to justify the trouble. Jonathan -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 11, 6:44 pm, Ben Finney [EMAIL PROTECTED] wrote: In such cases, the name 'dummy' is conventionally bound to the items from the iterator, for clarity of purpose:: for dummy in range(10): # do stuff that makes no reference to 'dummy' Is this documented? I've never heard of this convention. It's not PEP 8, and I've never seen consistent usage of any name. I'd be interested in knowing where you read that this was a convention, or in what subcommunities it's a convention in. I think dummy is a terrible name to use for this, since in no other usage I can think of does the word dummy suggest something isn't used. In fact, quite the opposite. For example, the dummy_threads module is most definitely used; the word dummy means that it's stripped down. Based on that, your usage of the symbol dummy above would suggest to me that it's a value used in lieu of something else (such as a calculated value). In mathematics, a dummy argument another name for the independent variable of a function (or more accurately, the symbol used to represent it), which also doesn't match your usage. If a value isn't used, then I think the most clear name for it is unused. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On Sun, 11 May 2008 18:52:48 -0700, Carl Banks wrote: On May 11, 6:44 pm, Ben Finney [EMAIL PROTECTED] wrote: In such cases, the name 'dummy' is conventionally bound to the items from the iterator, for clarity of purpose:: for dummy in range(10): # do stuff that makes no reference to 'dummy' Is this documented? I've never heard of this convention. It's not PEP 8, and I've never seen consistent usage of any name. I'd be interested in knowing where you read that this was a convention, or in what subcommunities it's a convention in. I think dummy is a terrible name to use for this, since in no other usage I can think of does the word dummy suggest something isn't used. In fact, quite the opposite. For example, the dummy_threads module is most definitely used; the word dummy means that it's stripped down. Based on that, your usage of the symbol dummy above would suggest to me that it's a value used in lieu of something else (such as a calculated value). In mathematics, a dummy argument another name for the independent variable of a function (or more accurately, the symbol used to represent it), which also doesn't match your usage. If a value isn't used, then I think the most clear name for it is unused. Carl Banks I agree with Carl. This group is the only place I've heard about this convension and it looks terrible IMO. Even if a value is not used, the variable still has a meaning: it is a counter, or an index. I know about the other convention: for i in xrange or for i in range. Wikipedia agrees with me: http://en.wikipedia.org/wiki/For_loop Examples in wikipedia article use either i or counter. It is established convention in almost every programming language and its origins are in mathematics (matrix indices). Google search for for dummy in range (with quotes) gives 164 results While for dummy in range gives 146 000 results. Almost thousand times more. So, i is more conventional and as such is more readable. -- Ivan -- http://mail.python.org/mailman/listinfo/python-list
Convention for name indicating don't care about the value (was: Is using range() in for loops really Pythonic?)
Carl Banks [EMAIL PROTECTED] writes: On May 11, 6:44 pm, Ben Finney [EMAIL PROTECTED] wrote: In such cases, the name 'dummy' is conventionally bound to the items from the iterator, for clarity of purpose:: for dummy in range(10): # do stuff that makes no reference to 'dummy' Is this documented? It's not a documented standard, to my knowledge. I've never heard of this convention. It's not PEP 8, and I've never seen consistent usage of any name. I'd be interested in knowing where you read that this was a convention, or in what subcommunities it's a convention in. It has been in this forum that the use of the name '_' for don't care about the value was deprecated, since that name is already overloaded with other meanings. I think dummy is a terrible name to use for this, since in no other usage I can think of does the word dummy suggest something isn't used. I think it's far superior to '_'. I'd be just as happy with any other name that explicitly distinguishes itself for this purpose. If a value isn't used, then I think the most clear name for it is unused. Sounds good to me. Now we merely need to convince the world. -- \ “Software patents provide one more means of controlling access | `\ to information. They are the tool of choice for the internet | _o__) highwayman.” —Anthony Taylor | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
Ben Finney wrote: John Salerno [EMAIL PROTECTED] writes: num = 33 for x in xrange(10): print num += 1 Which is better done by 'num += 10'. Can you come up with an example that isn't trivially replaced with clearer code? That might make it clearer what your concern is. ::sigh:: No, unfortunately I don't have a strong enough grasp of Python to give a really in-depth example. I understand what you're asking though. Perhaps people don't use this idiom as much as I think they do, so to give a trivial example to support my point isn't helpful. As far as I know, though, I think this is used often enough, so I thought I'd just ask if there are purists out there who don't like this use of the loop and feel it's an abuse of the syntax. -- http://mail.python.org/mailman/listinfo/python-list
Re: Convention for name indicating don't care about the value (was: Is using range() in for loops really Pythonic?)
On May 11, 11:41 pm, Ben Finney [EMAIL PROTECTED] wrote: Carl Banks [EMAIL PROTECTED] writes: On May 11, 6:44 pm, Ben Finney [EMAIL PROTECTED] wrote: In such cases, the name 'dummy' is conventionally bound to the items from the iterator, for clarity of purpose:: for dummy in range(10): # do stuff that makes no reference to 'dummy' Is this documented? It's not a documented standard, to my knowledge. I've never heard of this convention. It's not PEP 8, and I've never seen consistent usage of any name. I'd be interested in knowing where you read that this was a convention, or in what subcommunities it's a convention in. It has been in this forum that the use of the name '_' for don't care about the value was deprecated, since that name is already overloaded with other meanings. That doesn't follow at all from what you wrote: no one in this thread had even mentioned the usage of _ for unused values--how did you expect us to know you were talking about something no one brought up? So it seems that usage of dummy is not a convention, and avoidance of _ is not really a convention except on this group. I think dummy is a terrible name to use for this, since in no other usage I can think of does the word dummy suggest something isn't used. I think it's far superior to '_'. I'd be just as happy with any other name that explicitly distinguishes itself for this purpose. If a value isn't used, then I think the most clear name for it is unused. Sounds good to me. Now we merely need to convince the world. I'm happy to discourage the world from using _ for this purpose; ambivalent whether you even need to use a specific name. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
In such cases, the name 'dummy' is conventionally bound to the items from the iterator, for clarity of purpose [..] If a value isn't used, then I think the most clear name for it is unused. [...] Maybe my brain works differently, but I find both dummy and unused are extremely confusing names for loop counters. The loop begins to look like it doesn't iterate at all if its counter is dummy or unused. If it *counts* it is *used* and it's *not* dummy. Why reinvent the wheel when a common identifier naming convention is for the loop counter to use the variable names i, j and k (and so on if needed) (from Wikipedia http://en.wikipedia.org/wiki/Loop_counter ) -- Ivan -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno [EMAIL PROTECTED] writes: Ben Finney wrote: John Salerno [EMAIL PROTECTED] writes: num = 33 for x in xrange(10): print num += 1 Which is better done by 'num += 10'. Can you come up with an example that isn't trivially replaced with clearer code? That might make it clearer what your concern is. ::sigh:: No, unfortunately I don't have a strong enough grasp of Python to give a really in-depth example. It need not be in-depth, merely illustrative of the problem being addressed. I understand what you're asking though. Perhaps people don't use this idiom as much as I think they do, so to give a trivial example to support my point isn't helpful. I think that the idiom for unused in xrange(10): # do stuff with no reference to 'unused' is quite common. Is that what you're asking about? As far as I know, though, I think this is used often enough, so I thought I'd just ask if there are purists out there who don't like this use of the loop and feel it's an abuse of the syntax. No, it seems quite a normal usage of the syntax and a good use of an iterator. With do something N times, there must be *something* to keep track of which iteration we're up to (or, equivalently, how many iterations remain) at a given moment. A Python iterator seems a fine choice to hold that information, and better than many alternatives. -- \ My house is on the median strip of a highway. You don't really | `\notice, except I have to leave the driveway doing 60 MPH. -- | _o__)Steven Wright | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Is using range() in for loops really Pythonic?
I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno wrote: I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? Well, you should use xrange(10) instead of range(10). While range() returns a list of every single number, xrange() returns an iterable object that only generates them on-demand, so xrange(1) and xrange(sys.maxint) will use the same amount of RAM. (Not that it matters when it's only 10 items, of course.) Other than that, for i in xrange(10) is a standard Python idiom, even though it is a bit weird. -- -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? IMHO it's perfectly okay to use it as you describe it. Maybe you can switch to xrange( ) which doesn't return a list but an iterator. Note that in python 3.0 xrange will cease to exist and range( ) will return an iterator instead. Cheers, Daniel -- http://www.cafepress.com/putitdown -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 10, 8:19 pm, John Salerno [EMAIL PROTECTED] wrote: I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. x = range(10) print x --output:-- [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
On May 11, 3:19 am, John Salerno [EMAIL PROTECTED] wrote: I know it's popular and very handy, but I'm curious if there are purists out there who think that using something like: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. Anyone out there refuse to use it this way, or is it just impossible to avoid? Hi John, If you have an object that is both indexable and iterable, then visiting every member by first generating an index then indexing the object is un-pythonic. You should just iterate over the object. Like most rules, things can get fuzzy around the edges: if you have n objects to be visited each index at a time, then the more functional approach would be to izip all the objects and iterate over the result. Another way would be to iterate over the the enumeration of one object and use the index created to index the other n-1 objects. In all such situations you need to remember that things such as code clarity, and speed, might make the final decision for you. In the following examples then the first is what I would use, izip. If I needed an index then I'd prefer the last, which combines izip and enumerate: PythonWin 2.5 (r25:51908, Sep 19 2006, 09:52:17) [MSC v.1310 32 bit (Intel)] on win32. Portions Copyright 1994-2006 Mark Hammond - see 'Help/About PythonWin' for further copyright information. obj1 = 'CSM' obj2 = 'aue' obj3 = 'tmn' from itertools import izip for x,y,z in izip(obj1, obj2, obj3): ...print x,y,z ... C a t S u m M e n for i,x in enumerate(obj1): ...print x, obj2[i], obj3[i] ... C a t S u m M e n for i in range(len(obj1)): ...print obj1[i], obj2[i], obj3[i] ... C a t S u m M e n for i,(x,y,z) in enumerate(izip(obj1, obj2, obj3)): ...print i, x, y, z ... 0 C a t 1 S u m 2 M e n - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Is using range() in for loops really Pythonic?
John Salerno [EMAIL PROTECTED] writes: for x in range(10): #do something 10 times is unPythonic. The reason I ask is because the structure of the for loop seems to be for iterating through a sequence. It seems somewhat artificial to use the for loop to do something a certain number of times, like above. It is pretty natural in imperative-style code. The one thing I'd do differently is use xrange instead of range, to avoid creating a 10-element list in memory before starting the loop. -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
John Salerno wrote: The reason for this distinction comes from the fact that I read a lot how using range and for is somewhat discouraged, because it doesn't really use a for loop for it's true purpose. So my question is, is this just a Python-oriented opinion about for loops, or is it a general idea? The use of range in for loops is not discouraged, just the unnecessary use of it. In many languages, you were forced to use range - or size, or length, or count, etc - because the only practical method of iteration was to use successive indices into the array or other collection, stopping when the indexes run out. Most loops operate on some sort of structure in this way. In Python, you can iterate directly over the structure instead, so you no longer have to worry about keeping track of the current index, comparing it to the maximum index, or collecting the right object from the structure according to its index. Python just gives you the next object until there are none left. As a result, for most looping tasks, you have no need to use range or an equivalent. Also, what if you *do* need to just do something a set number of times. Is this okay, or does it mean you are approaching the problem incorrectly? Do you really need to do something a number of times? If so, range (or xrange) is perfect for the job. More often though, you need to do something once for every whatever, so put your 'whatevers' in a list and iterate over that. -- Ben Sizer -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
It's not just a Python thing, Java for example generally uses the
idiom:
for (Iterator it = list.iterator(); it.hasNext(); ) {
Object next = it.next();
//Do stuff to next
}
Horrible compared to the python idiom of course (though the latest
version supports for (x : list){})
Ruby has something similar in:
list.each do |item|
print item
end
Again, not as nice as the python idiom IMHO (Though there may be better
ways - I don't know Ruby very well).
So really, all modern programming languages seem to prefer the
loop-over-iterator idiom in preference to looping over a numerical
range.
--
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Re: using range() in for loops
John Salerno schreef: I'm reading Text Processing in Python right now and I came across a comment that is helping me to see for loops in a new light. I think because I'm used to the C-style for loop where you create a counter within the loop declaration, for loops have always seemed to me to be about doing something a certain number of times, and not about iterating over an object. The reason for this distinction comes from the fact that I read a lot how using range and for is somewhat discouraged, because it doesn't really use a for loop for it's true purpose. So my question is, is this just a Python-oriented opinion about for loops, or is it a general idea? Also, what if you *do* need to just do something a set number of times. Is this okay, or does it mean you are approaching the problem incorrectly? Using for and range together seems to be a common idiom, yet at the same time discouraged, so I'm wondering what is a good balance. I felt more or less the same when I first learned Python; I was also used to C-style loops, coming from a C/C++ background. In the end though, it turned out to be a non-issue for me. In many cases loops really are for iterating over sequences; more so than I realized when using for loops in C or C++. In these cases, Python's for statement works better than C-style loops. And if you really need to do something a certain number of times, there's still range() or xrange() to do it. It's quite simple, I think: - You have a sequence or iterator to loop over? Use for x in sequence. - You want something done a set number of times? Use for i in range(). - You want to loop over a sequence and also need the index? Use for i, x in enumerate(sequence). -- If I have been able to see further, it was only because I stood on the shoulders of giants. -- Isaac Newton Roel Schroeven -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
Roel Schroeven wrote: In many cases loops really are for iterating over sequences; more so than I realized when using for loops in C or C++. In these cases, Python's for statement works better than C-style loops. And if you really need to do something a certain number of times, there's still range() or xrange() to do it. Yeah, I'm starting to see the distinction now. I think one thing that confused me was that C# had two separate loops for these functionalities, the for loop and the foreach loop (which is equivalent to Python's for). But even when just doing something a number of times (C#'s for, Python's for), it looks much cleaner in Python because you don't have the long, messy three-part for statement. -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
Paul Rubin wrote: Normally you'd use range or xrange. range builds a complete list in memory so can be expensive if the number is large. xrange just counts up to that number. so when range would be used instead of xrange. if xrange is more efficient, why range was not reimplemented? -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
[EMAIL PROTECTED] wrote: hi John, Python doesn't provide for loop like C / C++ but using Range() or Xrange() you can achive all the functionalities of the C for loop. Not quite. Georg -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
AndyL wrote: Paul Rubin wrote: Normally you'd use range or xrange. range builds a complete list in memory so can be expensive if the number is large. xrange just counts up to that number. so when range would be used instead of xrange. if xrange is more efficient, why range was not reimplemented? Because of backwards compatibility. range() returns a list, xrange() an iterator: list(xrange(...)) will give the same results as range(...). In for loops, using xrange instead of range makes no difference since the loop only iterates over the range. But it's a problem when someone just does l = range(100) and assumes that he's got a list, probably doing l.remove(5) and so on. In Python 3000, plans are that range() will be the same as xrange() is now, and anyone needing a list can call list(range(...)). Georg -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
On Tue, 2006-04-04 at 21:54 -0400, John Salerno wrote:
I'm reading Text Processing in Python right now and I came across a
comment that is helping me to see for loops in a new light. I think
because I'm used to the C-style for loop where you create a counter
within the loop declaration, for loops have always seemed to me to be
about doing something a certain number of times, and not about iterating
over an object.
This is a normal reaction. Try to keep in mind that when you use any
higher level language your code will closer reflect what you want
rather than how to accomplish what you want. When you are creating a
loop over numbers, is your goal really to count, or to use the integer
that you are counting to do something else, like perhaps dereference
elements of a string.
Also, part of the problem is a preconceived restriction that you hold on
the use of forloops. They arn't just for counting, there are all sorts
of interesting things that can go in there. Remember, a for loop is
basically a while loop with a little bit of syntactic sugar. Look at
this:
for( a, b, c ) {
d;
e;
}
is the same as
a;
while (b)
{
d;
e;
c;
}
C for and while are the same creature. Python's while loop is Python's
version of for/while. If you wanted to mimick C you could write
i = 0
while( i10 ):
print i
i+=1
but this is clumbsy and slower. for(i=0;i10;i++) is a common enough
programing pattern, you arn't really interested in setting i,
incrementing, doing all of that housekeeping. You really want to repeat
10 times with with i set to 0, 1 ...
for ... xrange does this well and is somewhat the motivation for the
creation of xrange.
The reason for this distinction comes from the fact that I read a lot
how using range and for is somewhat discouraged, because it doesn't
really use a for loop for it's true purpose. So my question is, is this
Nothing in a well defined language has a true purpose. The true purpose
of an int in C isn't to be for loop fodder. One of the hallmarks of a
well designed language is orthogonality; most anything works with
anything else. A feature that has one specific use doesn't provide much
utility to justify the effort used to create it.
just a Python-oriented opinion about for loops, or is it a general idea?
Programming languages borrow from heavily from natural languages; yes,
for is a loaned word from English that exists in C, python ... lots of
languages. But just as when one human language borrows from another,
the resulting semantics are not always the same.
Each as a formal semantic. C and Python are somewhat different, and
yes, you could describe the philosophical difference as a matter of
opinions.
Also, what if you *do* need to just do something a set number of times.
Is this okay, or does it mean you are approaching the problem
incorrectly? Using for and range together seems to be a common idiom,
yet at the same time discouraged, so I'm wondering what is a good balance.
The correct idiom is for( xrange( foo )). This is preferred over range
for efficiency.
Historically there were no iters. If you wanted to do loop you would
say
for x in range( 10 ):
foo
bar
range created a list of 10 items and x marched over them. Creating this
list in advance doesn't need to take any more time; you have to create
the number objects anyway to assign to x at some point, so you might as
well get that done with upfront.
The problem was memory consumption. The memory requirements of the
list put a bound on large your iteration could be.
xrange was created, and soon followed general iters. Now, the range
object generates the numbers on the fly as the loop runs .. the loop
says hey, whats next and the next item is returned.
When people say don't say for x in range they are really saying use
xrange instead of range.
--
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Re: using range() in for loops
AndyL [EMAIL PROTECTED] wrote: Paul Rubin wrote: Normally you'd use range or xrange. range builds a complete list in memory so can be expensive if the number is large. xrange just counts up to that number. so when range would be used instead of xrange. if xrange is more efficient, why range was not reimplemented? If you actually want the list for some reason: $ python2.4 -mtimeit 'list(xrange(100))' 10 loops, best of 3: 4.54 usec per loop $ python2.4 -mtimeit 'range(100)' 10 loops, best of 3: 2.61 usec per loop -- \S -- [EMAIL PROTECTED] -- http://www.chaos.org.uk/~sion/ ___ | Frankly I have no feelings towards penguins one way or the other \X/ |-- Arthur C. Clarke her nu becomeþ se bera eadward ofdun hlæddre heafdes bæce bump bump bump -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
On Wed, 05 Apr 2006 09:16:37 -0400, AndyL wrote: Paul Rubin wrote: Normally you'd use range or xrange. range builds a complete list in memory so can be expensive if the number is large. xrange just counts up to that number. so when range would be used instead of xrange. if xrange is more efficient, why range was not reimplemented? For historical reasons. Don't worry, in Python3000, range() will be an iterator, and xrange() will disappear. Until then, I use range() for small loops (by small I mean anything up to a few tens of thousands), and xrange() only when I absolutely have to optimize my code to save a piddling few tens of kilobytes of memory. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
On Wed, 05 Apr 2006 16:15:12 +0200, Georg Brandl wrote: [EMAIL PROTECTED] wrote: hi John, Python doesn't provide for loop like C / C++ but using Range() or Xrange() you can achive all the functionalities of the C for loop. Not quite. Care to explain what the differences are, or shall we guess? -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
On Wed, 05 Apr 2006 16:21:02 +0200, Georg Brandl wrote: Because of backwards compatibility. range() returns a list, xrange() an iterator: list(xrange(...)) will give the same results as range(...). Georg is pretty much correct in his explanation, but just to dot all the I's and cross all the T's, we should explain that xrange() doesn't return an iterator, it returns a special xrange object: x = xrange(1000) type(x) type 'xrange' xrange existed as a special bit of magic before Python supported iterators. While xrange objects behave (sort of) like iterators, they aren't quite the same. For instance, they don't have a next attribute: x.next Traceback (most recent call last): File stdin, line 1, in ? AttributeError: 'xrange' object has no attribute 'next' whereas iterators do: i = iter(range(1000)) i.next method-wrapper object at 0xf7054d2c Likewise, you can get random access to the items in an xrange object: x[500] 500 but not in iterators: i[500] Traceback (most recent call last): File stdin, line 1, in ? TypeError: unsubscriptable object -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
Steven D'Aprano wrote: On Wed, 05 Apr 2006 16:21:02 +0200, Georg Brandl wrote: Because of backwards compatibility. range() returns a list, xrange() an iterator: list(xrange(...)) will give the same results as range(...). Georg is pretty much correct in his explanation, but just to dot all the I's and cross all the T's, we should explain that xrange() doesn't return an iterator, it returns a special xrange object: Ah yes, the old iterator - iterable problem ;) Georg -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
Steven D'Aprano wrote:
On Wed, 05 Apr 2006 16:15:12 +0200, Georg Brandl wrote:
[EMAIL PROTECTED] wrote:
hi John,
Python doesn't provide for loop like C / C++ but using Range() or
Xrange() you can achive all the functionalities of the C for loop.
Not quite.
Care to explain what the differences are, or shall we guess?
C's for is much more powerful.
for(a; b; c) { d } translates to
a
while b
d
c
which can't be replaced by a simple
for i in range(...)
Georg
--
http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
Georg Brandl [EMAIL PROTECTED] wrote:
Steven D'Aprano wrote:
On Wed, 05 Apr 2006 16:15:12 +0200, Georg Brandl wrote:
[EMAIL PROTECTED] wrote:
hi John,
Python doesn't provide for loop like C / C++ but using Range() or
Xrange() you can achive all the functionalities of the C for loop.
Not quite.
Care to explain what the differences are, or shall we guess?
C's for is much more powerful.
for(a; b; c) { d } translates to
a
while b
d
c
which can't be replaced by a simple
for i in range(...)
No, but it can be easily replaced by:
# factoring out the loopstructure...
def gotcha():
a
while b:
yield c
# ...from the loopbody
for i in gotcha():
d
or several variations thereof. In C++, I almost half-heartedly replace
most of Python's generators' power with C++'s templated iterators, but
when I program in C I find myself really straightjacketed these days in
NOT being able to pull out the loopstructure as I can in Python (and,
about halfway, in C++).
Alex
--
http://mail.python.org/mailman/listinfo/python-list
using range() in for loops
I'm reading Text Processing in Python right now and I came across a comment that is helping me to see for loops in a new light. I think because I'm used to the C-style for loop where you create a counter within the loop declaration, for loops have always seemed to me to be about doing something a certain number of times, and not about iterating over an object. The reason for this distinction comes from the fact that I read a lot how using range and for is somewhat discouraged, because it doesn't really use a for loop for it's true purpose. So my question is, is this just a Python-oriented opinion about for loops, or is it a general idea? Also, what if you *do* need to just do something a set number of times. Is this okay, or does it mean you are approaching the problem incorrectly? Using for and range together seems to be a common idiom, yet at the same time discouraged, so I'm wondering what is a good balance. Thanks. -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
John Salerno [EMAIL PROTECTED] writes: The reason for this distinction comes from the fact that I read a lot how using range and for is somewhat discouraged, because it doesn't really use a for loop for it's true purpose. So my question is, is this just a Python-oriented opinion about for loops, or is it a general idea? Normally you'd use range or xrange. range builds a complete list in memory so can be expensive if the number is large. xrange just counts up to that number. -- http://mail.python.org/mailman/listinfo/python-list
Re: using range() in for loops
hi John, Python doesn't provide for loop like C / C++ but using Range() or Xrange() you can achive all the functionalities of the C for loop.If you wants distributed for loop You can use Xrange. John Salerno wrote: I'm reading Text Processing in Python right now and I came across a comment that is helping me to see for loops in a new light. I think because I'm used to the C-style for loop where you create a counter within the loop declaration, for loops have always seemed to me to be about doing something a certain number of times, and not about iterating over an object. The reason for this distinction comes from the fact that I read a lot how using range and for is somewhat discouraged, because it doesn't really use a for loop for it's true purpose. So my question is, is this just a Python-oriented opinion about for loops, or is it a general idea? Also, what if you *do* need to just do something a set number of times. Is this okay, or does it mean you are approaching the problem incorrectly? Using for and range together seems to be a common idiom, yet at the same time discouraged, so I'm wondering what is a good balance. Thanks. -- http://mail.python.org/mailman/listinfo/python-list
