[Tutor] functions and default argument

[Albert-Jan Roskam]

Interesting thread and webpages. Insightful, but is this really used as a technique in daily practice? It feels a bit like a hack to me. Like the author of one of the websites said: rule #1 don't mess with this.

 
Cheers!!
Albert-Jan


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>________________________________
>From: "Prasad, Ramit" <ramit.prasad at jpmorgan.com>
>To: "tutor at python.org" <tutor at python.org>
>Sent: Friday, October 21, 2011 9:40 PM
>Subject: Re: [Tutor] functions and default argument
>
>>The same thing occurs when you use a mutable object like a list or a 
>>dict. The default value is assigned once, and once only. But notice that 
>>you can modify the default value, say by appending to it:
>
>Not sure this will work exactly the same way in other IDEs, but in mine:
>
>>>> a = []
>>>> def foo(x=a):
>...     x.append(1)
>...    
>>>> a.append( 2 )
>>>> foo()
>>>> print a
>[2, 1]
>>>> help(foo)
>Help on function foo in module __pieshell__:
>
>foo(x=[2, 1])
>
>>>> foo()
>>>> help(foo)
>Help on function foo in module __pieshell__:
>
>foo(x=[2, 1, 1])
>
>>>> a.append( 3 )
>>>> help(foo)
>Help on function foo in module __pieshell__:
>
>foo(x=[2, 1, 1, 3])
>>>> b = []
>>>> foo(b)
>>>> b
>[1]
>
>
>Notice how it is always bound to the list a, but can be "overridden".
>
>I know this has been discussed on this list or the main list before if you take a look through the archives.
>Sorry I can't remember what the thread would be like or when it was :(
>http://stackoverflow.com/questions/1132941/least-astonishment-in-python-the-mutable-default-argument 
>
>
>Ramit
>
>
>Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
>712 Main Street | Houston, TX 77002
>work phone: 713 - 216 - 5423
>
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