Re: [Tutor] Do something on list elements
On 07/27/2018 04:32 PM, Cameron Simpson wrote: > On 27Jul2018 23:06, Alan Gauld wrote: >> In Python you very rarely need to resort to using indexes >> to process the members of a collection. And even more rarely >> do you need to manually increment the index. I think this was an important point: use a list index only when the actual value of the index is important, otherwise use the fact that a list is iterable by just looping over the list itself without bothering with indices... it's a powerful enough idea that C++. C# and other languages picked it up. > I use indices when I need to modify the elements of a list in place. The > list comprehension makes a shiny new list. That is usually fine, but not > always what is required. True indeed, but in this case since the elements being modified are strings, which are immutable and thus "modifying" a string creates a new string, we're not really buying anything by not creating a new list of those new strings along the way... ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Do something on list elements
On 27/07/18 23:32, Cameron Simpson wrote:
>> for index, s in l:
>> l[index] = s.replace('X','')
>> print(l)
>
> I think you meant:
>
> for index, s in enumerate(l):
Oops, yes. Sorry.
>> In Python you very rarely need to resort to using indexes
>> to process the members of a collection. And even more rarely
>> do you need to manually increment the index.
>
> I use indices when I need to modify the elements of a list in place.
Yes, that's probably the most common use case, and
enumerate is the best way to do that.
> comprehension makes a shiny new list. That is usually fine, but not always
> what
> is required.
>From a purist point of view its usually preferable but in
practice making copies of large data structures is usually
a bad idea. In that case you are forced to resort to
enumerate, I agree.
> The other place I use enumerate in a big way is to track line numbers in
> files,
> as context for error messages (either now or later). For example:
Yes, but then you don't use the index to access/process
the data. Its just providing context.
--
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] Do something on list elements
On 27Jul2018 23:06, Alan Gauld wrote:
On 27/07/18 13:56, Valerio Pachera wrote:
l = ['unoX', 'dueX']
c = 0
for n in l:
l[c] = l[c].replace('X','')
c = c + 1
print (l)
it works but I wonder if there's a better way to achieve the same.
Yes, a much better way.
for index, s in l:
l[index] = s.replace('X','')
print(l)
I think you meant:
for index, s in enumerate(l):
But better still is a list comprehension:
l = [s.replace('X','') for s in l)
print(l)
In Python you very rarely need to resort to using indexes
to process the members of a collection. And even more rarely
do you need to manually increment the index.
I use indices when I need to modify the elements of a list in place. The list
comprehension makes a shiny new list. That is usually fine, but not always what
is required.
I also have (rare) occasions where an item wants know its own index. In that
case one wants the index floating around so it can be attached to the item.
The other place I use enumerate in a big way is to track line numbers in files,
as context for error messages (either now or later). For example:
with open(filename) as f:
for lineno, line in enumerate(f, 1):
if badness:
print("%s:%d: badness happened" % (filename, lineno), file=sys.stderr)
continue
... process good lines ...
Cheers,
Cameron Simpson
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Re: [Tutor] Do something on list elements
On 27/07/18 13:56, Valerio Pachera wrote:
> l = ['unoX', 'dueX']
> c = 0
> for n in l:
> l[c] = l[c].replace('X','')
> c = c + 1
> print (l)
> ---
>
> it works but I wonder if there's a better way to achieve the same.
Yes, a much better way.
for index, s in l:
l[index] = s.replace('X','')
print(l)
But better still is a list comprehension:
l = [s.replace('X','') for s in l)
print(l)
In Python you very rarely need to resort to using indexes
to process the members of a collection. And even more rarely
do you need to manually increment the index.
--
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] how to change the command "string" on a tkinter Button?
On 27/07/18 11:55, Shall, Sydney wrote: > On 01/07/2018 11:19, Steven D'Aprano wrote: >> Even better would be to learn a form of VCS (version control system) >> such as Mercurial (hg) or git. Depending on the text editor you are >> using, it may have VCS integration available. > > Does Spyder have a VCS? Dunno, sorry... > Could you list a few text-editors that do have VCS, please. It's not so much that they have a VCS but that they integrate with an existing VCS. So they will typically have menu options for checking in/out a file or locking/unlocking it. Typically you can configure which VCS they use from a list of common options, in some cases you can define the command line to use for each menu action. vim, emacs, Eclipse, Netbeans, VisualStudio etc all support VCS to varying degrees. But you still need to install and configure a VCS engine such as CVS, SVN, Hg or git etc. -- 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
[Tutor] Do something on list elements
Hi all, I started studying python and I hope you may help me getting better.
Let's start with the first question.
Consider this example
---
#!/usr/bin/python3
l = ['unoX', 'dueX']
c = 0
for n in l:
l[c] = l[c].replace('X','')
c = c + 1
print (l)
---
it works but I wonder if there's a better way to achieve the same.
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Re: [Tutor] how to change the command "string" on a tkinter Button?
On 01/07/2018 11:19, Steven D'Aprano wrote: On Sun, Jul 01, 2018 at 03:32:59PM +1000, Chris Roy-Smith wrote: "Save As..." before engaging in big changes is your friend :-) Even better would be to learn a form of VCS (version control system) such as Mercurial (hg) or git. Depending on the text editor you are using, it may have VCS integration available. Does Spyder have a VCS? Could you list a few text-editors that do have VCS, please. -- _ Professor Sydney Shall Department of Haematology/Oncology Phone: +(0)2078489200 E-Mail: sydney.shall [Correspondents outside the College should add @kcl.ac.uk] ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Questions about the formatting of docstrings
On 07/27/2018 11:23 AM, boB Stepp wrote: > On Fri, Jul 27, 2018 at 12:50 AM Steven D'Aprano wrote: >> >> On Thu, Jul 26, 2018 at 11:34:11PM -0500, boB Stepp wrote: > >>> (1) The author claims that reStructuredText is the official Python >>> documentation standard. Is this true? If yes, is this something I >>> should be doing for my own projects? >> >> Yes, it is true. If you write documentation for the Python standard >> library, they are supposed to be in ReST. Docstrings you read in >> the interactive interpreter often aren't, but the documentation you read >> on the web page has all been automatically generated from ReST text >> files. > > What tool is being used to generate the documentation from the ReST text > files? I'm not sure if Python is still using it, but Sphinx is a popular choice, originally written to handle the Python docs. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Questions about the formatting of docstrings
On Fri, Jul 27, 2018 at 12:50 AM Steven D'Aprano wrote: > > On Thu, Jul 26, 2018 at 11:34:11PM -0500, boB Stepp wrote: > > (1) The author claims that reStructuredText is the official Python > > documentation standard. Is this true? If yes, is this something I > > should be doing for my own projects? > > Yes, it is true. If you write documentation for the Python standard > library, they are supposed to be in ReST. Docstrings you read in > the interactive interpreter often aren't, but the documentation you read > on the web page has all been automatically generated from ReST text > files. What tool is being used to generate the documentation from the ReST text files? Thanks! boB ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
