Re: [Tutor] help with exercise 15 of zed shaw's LPTHW
On 06/07/16 15:04, loh...@tuta.io wrote:
> script, filename = argv
> txt = open (filename)
>
> print "Here's your file %r: " % filename
> print txt.read()
>
> print "Type the filename again: "
> file_again = raw_input("> ")
>
> txt_again = open(file_again)
> print txt_again.read()
> why do I have to create a variable txt_again to assign it to the open
> function and them print the file?
You don't, and could get away with a single
variable - filename. Like this:
filename = argv[1]
print "Here's your file %r: " % filename
print open(filename).read()
filename = raw_input("Type the filename again: >")
print open(filename).read()
But your book is (I assume) trying to teach you
good practice.
While you could have just printed the result of read directly,
its better not to over complicate code by doing too much in one
line (for a start, its harder to debug) the same variable.
Variables are cheap to create and if given useful names
tell us a lot about the purpose of the code.
In this case it's all a bit trivial, just printing the file
content, but if you were doing more complex processing
storing the file (and data) in variables would be the
best choice.
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos
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Re: [Tutor] help with exercise 15 of zed shaw's LPTHW
On Wed, Jul 6, 2016 at 10:59 AM wrote:
> why do I have to create a variable txt_again to assign it to the open
> function and them print the file?
> why is it that I can't only write something like open(file_again).read()?
>
Good insight. In fact you don't need to create the variable. The code ``data
= open('filename').read()`` will open the file named "filename" in the
current working directory, read it, and assign the data to a variable.
However, many programmers use variables not because they must, but because
good variable names can make code easier to read. Also, doing less stuff on
a line of code can make that code easier to read.
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Re: [Tutor] help with exercise 15 of zed shaw's LPTHW
first, sorry everyone for having attached the file instead of just typing it
here.
second, thanks a lot for the replies; even though I gave you no code it was
quite helpful!
the code was this:
from sys import argv
script, filename = argv
txt = open (filename)
print "Here's your file %r: " % filename
print txt.read()
print "Type the filename again: "
file_again = raw_input("> ")
txt_again = open(file_again)
print txt_again.read()
Peter Otten explained it to me line by line [thanks so much :)] however, I do
have one more question:
why do I have to create a variable txt_again to assign it to the open
function and them print the file?
why is it that I can't only write something like open(file_again).read()?
6. Jul 2016 05:22 by __pete...@web.de:
> loh...@tuta.io> wrote:
>
>> hey everyone. this is my first time trying this -- actually, I've been
>> studying python only for some days now, and I'm afraid my questions are
>> going to be rally simple, but I can't seem to understand this piece of
>> code and thus can't move on.
>
> You seem to be talking about
>
> http://learnpythonthehardway.org/book/ex15.html
>
> """
> from sys import argv
>
> script, filename = argv
>
> txt = open(filename)
>
> print "Here's your file %r:" % filename
> print txt.read()
>
> print "Type the filename again:"
> file_again = raw_input("> ")
>
> txt_again = open(file_again)
>
> print txt_again.read()
> """
>
> As others said, always provide the code you are asking about, or if that is
> not possible at least provide a link.
>
>> you probably know the book, so you know that zed always makes us write
>> code so that then we can understand how it works, and it's great, but in
>> this exercise there are just too many new functions and without
>> explanation they are a bit hard to understand... so I'm having trouble
>> with most of the lines here.
>>
>> it's not that I want the full explanation to that code, but since I'm
>> unfamiliar with some of its concepts, I'm just going to tell you all the
>> things that I don't understand (sorry for it being a lot):
>> 1. the need to put script into an estipulation for argv (line 3)
>
> Write a script tmp.py containing
>
> from sys import argv
> print argv
>
> then call it with with one parameter, e. g.
>
> $ python tmp.py somefile.txt
> ['tmp.py', 'somefile.txt']
>
> As you can see argv is a list with two items, the first being "tmp.py", the
> name of the script you are invoking. You are only interested in the second
> one, the filename. The easy way to get that is
>
> filename = argv[1]
>
> the hard way is to use "unpacking"
>
> script, filename = argv
>
> where python will assign one item from the list on the right to every name
> on the left:
>
items = ["foo", "bar"]
one, two = items
one
> 'foo'
two
> 'bar'
>
> What happens if the number of names on the left doesn't match the number of
> items in the list?
>
one, two, three = items
> Traceback (most recent call last):
> File "", line 1, in
> ValueError: need more than 2 values to unpack
>
> You get an exception. That is why you have to provide the name "script" in
> Zed's example even though you are not actually interested in the script
> name.
>
>> 2. the what is txt and why it has to be used there (line 4)
>
> txt is a file object and
>
>> 3. txt.read() -- which are all new functions(? I dont even know what they
>> are) (line 7)
>
> read() is a method that here reads the whole file into a string. You use
> the
> open() function to open a file and usually assign the file object that is
> returned by open to a name. You can freely choose that name. The structure
> is the same for every object, be it a number:
>
> x = 42 # assign a number to x
> y = x + x # do some arithmetic with x and assign the result to y
> print y # print the result
>
> a list:
>
> mynumbers = list() # create a list
> mynumbers.append(42) # append a number to the list
> print mynumbers # print the list
>
> or a file:
>
> myfile = open("example.txt") # open the file example.txt in the current
> # working directory. If the file doesn't
> exist
> # you get an error
>
> print "first line:", myfile.readline() # read the first line and print it
> print "rest of the file:"
> print myfile.read() # read the rest of the file and print it
>
> myfile.close() # close the file
>
>> 4. file_again (line 10)
>> 5. txt_again (line 12)
>> and line 14.
>
> 4. and 5. are just a repetition of the first part, with the variation that
> the filename, assigned to file_again is read interactively with raw_input()
> instead of passing it as a commandline argument to the script.
>
> The names used can be freely chosen by the programmer, a script
>
> from sys import argv
>
> red_apple, my_hat = argv
>
> blue_suede_shoes = open(my_hat)
> print blue_suede_shoes.read()
> blue_suede_shoes.close()
>
> would work exactly like the first part of the hard-way example. However,
> picking descrip
Re: [Tutor] help with exercise 15 of zed shaw's LPTHW
loh...@tuta.io wrote:
> hey everyone. this is my first time trying this -- actually, I've been
> studying python only for some days now, and I'm afraid my questions are
> going to be rally simple, but I can't seem to understand this piece of
> code and thus can't move on.
You seem to be talking about
http://learnpythonthehardway.org/book/ex15.html
"""
from sys import argv
script, filename = argv
txt = open(filename)
print "Here's your file %r:" % filename
print txt.read()
print "Type the filename again:"
file_again = raw_input("> ")
txt_again = open(file_again)
print txt_again.read()
"""
As others said, always provide the code you are asking about, or if that is
not possible at least provide a link.
> you probably know the book, so you know that zed always makes us write
> code so that then we can understand how it works, and it's great, but in
> this exercise there are just too many new functions and without
> explanation they are a bit hard to understand... so I'm having trouble
> with most of the lines here.
>
> it's not that I want the full explanation to that code, but since I'm
> unfamiliar with some of its concepts, I'm just going to tell you all the
> things that I don't understand (sorry for it being a lot):
> 1. the need to put script into an estipulation for argv (line 3)
Write a script tmp.py containing
from sys import argv
print argv
then call it with with one parameter, e. g.
$ python tmp.py somefile.txt
['tmp.py', 'somefile.txt']
As you can see argv is a list with two items, the first being "tmp.py", the
name of the script you are invoking. You are only interested in the second
one, the filename. The easy way to get that is
filename = argv[1]
the hard way is to use "unpacking"
script, filename = argv
where python will assign one item from the list on the right to every name
on the left:
>>> items = ["foo", "bar"]
>>> one, two = items
>>> one
'foo'
>>> two
'bar'
What happens if the number of names on the left doesn't match the number of
items in the list?
>>> one, two, three = items
Traceback (most recent call last):
File "", line 1, in
ValueError: need more than 2 values to unpack
You get an exception. That is why you have to provide the name "script" in
Zed's example even though you are not actually interested in the script
name.
> 2. the what is txt and why it has to be used there (line 4)
txt is a file object and
> 3. txt.read() -- which are all new functions(? I dont even know what they
> are) (line 7)
read() is a method that here reads the whole file into a string. You use the
open() function to open a file and usually assign the file object that is
returned by open to a name. You can freely choose that name. The structure
is the same for every object, be it a number:
x = 42 # assign a number to x
y = x + x # do some arithmetic with x and assign the result to y
print y # print the result
a list:
mynumbers = list() # create a list
mynumbers.append(42) # append a number to the list
print mynumbers # print the list
or a file:
myfile = open("example.txt") # open the file example.txt in the current
# working directory. If the file doesn't exist
# you get an error
print "first line:", myfile.readline() # read the first line and print it
print "rest of the file:"
print myfile.read() # read the rest of the file and print it
myfile.close() # close the file
> 4. file_again (line 10)
> 5. txt_again (line 12)
> and line 14.
4. and 5. are just a repetition of the first part, with the variation that
the filename, assigned to file_again is read interactively with raw_input()
instead of passing it as a commandline argument to the script.
The names used can be freely chosen by the programmer, a script
from sys import argv
red_apple, my_hat = argv
blue_suede_shoes = open(my_hat)
print blue_suede_shoes.read()
blue_suede_shoes.close()
would work exactly like the first part of the hard-way example. However,
picking descriptive names and using them consistently makes it much easier
for a human reader to understand what's going on.
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Re: [Tutor] help with exercise 15 of zed shaw's LPTHW
On 06/07/16 00:56, loh...@tuta.io wrote: > hey everyone. this is my first time trying this Welcome, but... > you probably know the book, Sorry, I don't and I suspect I'm not alone. It's probably a fine book, but we don't all know it. > so you know that zed always makes us write code > so that then we can understand how it works, Good man Zed :-) > exercise there are just too many new functions and without explanation they > are a bit hard to understand... so I'm having trouble with most of the lines > here. And here's the next problem. This is a text based mailing list. As such the server often strips out attachments as potential security risks. So we can't see the code (I'm assuming you attached it?) > 1. the need to put script into an estipulation for argv (line 3) > 2. the what is txt and why it has to be used there (line 4) > 3. txt.read() -- which are all new functions(? I dont even know what they > are) (line 7) > 4. file_again (line 10) > 5. txt_again (line 12) > and line 14. Without sight of the code its hard to know what's going on. But I suspect some of these "functions" are actually variables (or objects) and hopefully zed has already discussed those? Can you repost but include your code inside the mail message. Also try to post in plain text since HTML tends to get garbled in transit. HTH -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.amazon.com/author/alan_gauld Follow my photo-blog on Flickr at: http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] help with exercise 15 of zed shaw's LPTHW
On Tue, Jul 5, 2016 at 8:24 PM wrote: > I'm having trouble with most of the lines here. > It looks like you tried to attach a file. This mailing list does not allow attachments. Instead, could you paste the code into your email? > things that I don't understand: > 1. the need to put script into an estipulation for argv (line 3) > 2. the what is txt and why it has to be used there (line 4) > 3. txt.read() -- which are all new functions(? I dont even know what they > are) (line 7) > I'm guessing txt is a file object or a file-like object that supports the .read method to read the entire contents of the file into a single string object. > 4. file_again (line 10) > 5. txt_again (line 12) > and line 14. > ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] help with exercise 15 of zed shaw's LPTHW
Hi Heloisa, and welcome. Do you have a link to the code? Or better still, if it is short (say under fifty lines) can you copy it into an email and send it? On Wed, Jul 06, 2016 at 12:56:19AM +0100, loh...@tuta.io wrote: [...] > 1. the need to put script into an estipulation for argv (line 3) I'm sorry, I don't know what that word "estipulation" means. Do you mean "stipulation", as in: That which is stipulated, or agreed upon; that which is definitely arranged or contracted; an agreement > 2. the what is txt and why it has to be used there (line 4) > 3. txt.read() -- which are all new functions(? I dont even know what they > are) (line 7) > 4. file_again (line 10) > 5. txt_again (line 12) > and line 14. The only thing I can guess without seeing the code is that MAYBE txt is an open file, and txt.read() reads the content of the file. -- Steve ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] help with exercise 15 of zed shaw's LPTHW
Welcome! On 07/05/2016 06:56 PM, loh...@tuta.io wrote: hey everyone. this is my first time trying this -- actually, I've been studying python only for some days now, and I'm afraid my questions are going to be rally simple, but I can't seem to understand this piece of code and thus can't move on. you probably know the book, so you know that zed always makes us write code so that then we can understand how it works, and it's great, but in this exercise there are just too many new functions and without explanation they are a bit hard to understand... so I'm having trouble with most of the lines here. While this book is fairly well known, not everyone has a copy at hand. I would suggest that you resend your email with the full exercise typed into its body (This list does not accept attachments BTW.), and then pose your questions. This way you provide the necessary context *in* your email body, so that everyone can follow along. Cheers! boB ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] help with exercise 15 of zed shaw's LPTHW
hey everyone. this is my first time trying this -- actually, I've been studying python only for some days now, and I'm afraid my questions are going to be rally simple, but I can't seem to understand this piece of code and thus can't move on. you probably know the book, so you know that zed always makes us write code so that then we can understand how it works, and it's great, but in this exercise there are just too many new functions and without explanation they are a bit hard to understand... so I'm having trouble with most of the lines here. it's not that I want the full explanation to that code, but since I'm unfamiliar with some of its concepts, I'm just going to tell you all the things that I don't understand (sorry for it being a lot): 1. the need to put script into an estipulation for argv (line 3) 2. the what is txt and why it has to be used there (line 4) 3. txt.read() -- which are all new functions(? I dont even know what they are) (line 7) 4. file_again (line 10) 5. txt_again (line 12) and line 14. as you can see, it's pretty much everything. sorry about that. I'd really appreciate any help at all! thanks a lot, heloisa ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
