Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #11780

Re: lists and for loops

Show all headers | View raw

On Wed, 17 Aug 2011 20:08:23 -0700 (PDT), Emily Anne Moravec wrote:
> I want to add 5 to each element of a list by using a for loop.
>
> Why doesn't this work?
>
> numbers = [1, 2, 3, 4, 5]
> for n in numbers:
>      n = n + 5
> print numbers

Because integers are immutable.  You cannot turn 1 into 6.
Contrast this behavior with lists, which *are* mutable:

>>> numbers = [[1],[2],[3],[4],[5]]
>>> for n in numbers:
...   n[0]= n[0] + 5
... 
>>> numbers
[[6], [7], [8], [9], [10]]

For practical purposes, I'm sure you'll find other responders'
excellent posts to be of more immediate use, but keeping
mutability in mind helps.

-- 
To email me, substitute nowhere->spamcop, invalid->net.

Back to comp.lang.python | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

lists and for loops Emily Anne Moravec <moravec@stolaf.edu> - 2011-08-17 20:08 -0700
  Re: lists and for loops alex23 <wuwei23@gmail.com> - 2011-08-17 20:23 -0700
    Re: lists and for loops Mark Niemczyk <prahamark@gmail.com> - 2011-08-18 05:22 -0700
      Re: lists and for loops Tim Chase <python.list@tim.thechases.com> - 2011-08-18 07:45 -0500
  Re: lists and for loops Peter Pearson <ppearson@nowhere.invalid> - 2011-08-18 16:43 +0000

csiph-web