Re: Curious function argument

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From	Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject	Re: Curious function argument
Date	Wed, 12 Nov 2014 09:18:30 -0500
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On Wed, 12 Nov 2014 14:07:14 +0100, "ast" <nomail@invalid.com> declaimed
the following:

>Hello
>
>I saw in a code from a previous message in this forum
>a curious function argument.
>
>def test(x=[0]):
>   print(x[0])   ## Poor man's object
>   x[0] += 1
>
>>>> test()
>0
>>>> test()
>1
>>>> test()
>2
>>>> 
>
>I understand that the author wants to implement a global
>variable x . It would be better to write 'global x' inside the
>function.
>
	No... The author implemented a mutable DEFAULT argument.

	The argument can still be overloaded by passing something else into the
function.

y = [0]
z = 234
test(y)
test(z)

	This would not work if one instead declared a global "x"
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

Thread

Curious function argument "ast" <nomail@invalid.com> - 2014-11-12 14:07 +0100
  Re: Curious function argument Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-12 14:03 +0000
  Re: Curious function argument Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-11-12 09:18 -0500
  Re: Curious function argument Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-15 21:39 +1100
  Re: Curious function argument Akira Li <4kir4.1i@gmail.com> - 2014-11-28 08:52 +0300

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