Re: a clarification on the "global" statement sought

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From	Chris Angelico <rosuav@gmail.com>
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Subject	Re: a clarification on the "global" statement sought
Date	Fri, 11 Mar 2016 20:29:47 +1100
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On Fri, Mar 11, 2016 at 8:09 PM, Charles T. Smith
<cts.private.yahoo@gmail.com> wrote:
>   "Python deals with variables the other way around.
>    They are local, if not otherwise declared.
>    ...
>     def f():
>         print(s)
>     s = "I love Paris in the summer!"
>     f()
>     ...
>     As there is no local variable s, i.e. no assignment to s, the value
>     from the ***global*** variable s will be used."
>
> Indeed "maverick": that a variable can be an undefined global
> and then only appears as such when assigned to, has caused me
> no end of grief.

Looking purely at the function definition, you can see with 100%
certainty that it references two non-local names: "print" and "s".
Neither is assigned to within the function, so both are looked up
externally. At run time, s is resolved as a module-level name; print
is not, so Python looks further, to the builtins. Had s not been
assigned to, it would still be a global name in the function, but it
would fail to be found in either the module namespace or the builtins,
and would result in NameError. But either way, it's a global name,
whether it's assigned to or not.

ChrisA

Thread

a clarification on the "global" statement sought "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2016-03-11 08:13 +0000
  Re: a clarification on the "global" statement sought Chris Angelico <rosuav@gmail.com> - 2016-03-11 19:29 +1100
    Re: a clarification on the "global" statement sought "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2016-03-11 08:53 +0000
      Re: a clarification on the "global" statement sought Peter Otten <__peter__@web.de> - 2016-03-11 10:23 +0100
  Re: a clarification on the "global" statement sought Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-11 08:31 +0000
    Re: a clarification on the "global" statement sought "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2016-03-11 09:09 +0000
      Re: a clarification on the "global" statement sought Chris Angelico <rosuav@gmail.com> - 2016-03-11 20:29 +1100
  Re: a clarification on the "global" statement sought eryk sun <eryksun@gmail.com> - 2016-03-11 03:20 -0600

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