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

Groups > comp.lang.python > #6551

Re: scope of function parameters

Show all headers | View raw

On Sun, 29 May 2011 04:30:52 -0400, Henry Olders wrote: 
[snip]
> def main():
> 	a = ['a list','with','three elements']
> 	print a
> 	print fnc1(a)
> 	print a
> 	
> def fnc1(b):
> 	return fnc2(b)
>
> def fnc2(c):
> 	c[1] = 'having'
> 	return c
>
> This is the output:
> ['a list', 'with', 'three elements']
> ['a list', 'having', 'three elements']
> ['a list', 'having', 'three elements']
>
> I had expected the third print statement to give the same
> output as the first, but variable a had been changed by
> changing variable c in fnc2.

For what it's worth, I've noticed that use of the word "variable"
is correlated with a misunderstanding of Python's way of doing
things.  

"Variable" seems to connote a box that has something in it,
so when fnc1 passes b to fnc2 which calls it c, you think
you have a box named b and a box named c, and you wonder
whether the contents of those boxes are the same or
different.

Python works in terms of objects having names, and one
object can have many names.  In your example, fnc1 works
with an object that it calls b, and which it passes to fnc2,
but fnc2 chooses to call that same object c.  The names b
and c aren't boxes that hold things, they are -- in the
words of one of this group's old hands -- sticky-note labels
that have been slapped on the same object.

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

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

Thread

scope of function parameters Henry Olders <henry.olders@mcgill.ca> - 2011-05-29 04:30 -0400
  Re: scope of function parameters Mel <mwilson@the-wire.com> - 2011-05-29 07:59 -0400
    Re: scope of function parameters Terry Reedy <tjreedy@udel.edu> - 2011-05-29 16:27 -0400
  Re: scope of function parameters Peter Pearson <ppearson@nowhere.invalid> - 2011-05-29 17:21 +0000
    Re: scope of function parameters Ben Finney <ben+python@benfinney.id.au> - 2011-05-30 07:42 +1000
      Re: scope of function parameters Laurent Claessens <moky.math@gmail.com> - 2011-05-30 09:12 +0200
        Re: scope of function parameters Chris Rebert <clp2@rebertia.com> - 2011-05-30 00:27 -0700
        Re: scope of function parameters Laurent <moky.math@gmail.com> - 2011-05-30 09:38 +0200
        Re: scope of function parameters Daniel Kluev <dan.kluev@gmail.com> - 2011-05-30 19:10 +1100
        Re: scope of function parameters Terry Reedy <tjreedy@udel.edu> - 2011-05-30 05:02 -0400
          Re: scope of function parameters Laurent Claessens <moky.math@gmail.com> - 2011-05-30 11:08 +0200
            Re: scope of function parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-30 09:14 +0000
            Re: scope of function parameters Ben Finney <ben+python@benfinney.id.au> - 2011-05-30 19:17 +1000
            Re: scope of function parameters Peter Otten <__peter__@web.de> - 2011-05-30 11:41 +0200
              Re: scope of function parameters Laurent Claessens <moky.math@gmail.com> - 2011-05-30 12:10 +0200
              Re: scope of function parameters Laurent Claessens <moky.math@gmail.com> - 2011-05-30 12:10 +0200
            Re: scope of function parameters Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-05-30 13:40 +0300
            Re: scope of function parameters Terry Reedy <tjreedy@udel.edu> - 2011-05-30 12:49 -0400
        Re: scope of function parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-30 09:16 +0000
  Re: scope of function parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-29 23:46 +0000
    Re: scope of function parameters Ben Finney <ben+python@benfinney.id.au> - 2011-05-30 11:31 +1000
      Re: scope of function parameters Chris Angelico <rosuav@gmail.com> - 2011-05-30 11:56 +1000
        Re: scope of function parameters Ben Finney <ben+python@benfinney.id.au> - 2011-05-30 12:08 +1000
          Re: scope of function parameters Chris Angelico <rosuav@gmail.com> - 2011-05-30 12:37 +1000
      Re: scope of function parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-30 04:23 +0000
  Re: scope of function parameters rusi <rustompmody@gmail.com> - 2011-05-31 09:46 -0700
    Re: scope of function parameters rusi <rustompmody@gmail.com> - 2011-05-31 10:33 -0700

csiph-web