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Re: When do default parameters get their values set?

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On Tue, Dec 9, 2014 at 9:10 AM, bSneddon <w.g.sneddon@gmail.com> wrote:
> I ran into an issue setting variables from a GUI module that imports a back end module.  My approach was wrong obviously but what is the best way to set values in a back end module.
>
> #module name beTest.py
>
> cfg = { 'def' : 'blue'}
>
> def printDef(argT = cfg['def']):
>         print argT

They're set when you define the function, and become attributes of the function.

If you want to lazily fetch the defaults, here's one common idiom:

def printDef(argT=None):
    """Print the argT value, defaults to cfg['def']"""
    if argT is None: argT = cfg['def']
    print(argT)

This depends on None not being a meaningful argument value, of course.
If you need to have any object at all able to be passed in, you'd need
to create a dedicated sentinel object, or use *args and unpack
yourself; but for a lot of cases, None works fine.

ChrisA

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Thread

When do default parameters get their values set? bSneddon <w.g.sneddon@gmail.com> - 2014-12-08 14:10 -0800
  Re: When do default parameters get their values set? Chris Angelico <rosuav@gmail.com> - 2014-12-09 09:28 +1100
  Re: When do default parameters get their values set? Chris Kaynor <ckaynor@zindagigames.com> - 2014-12-08 14:28 -0800
  Re: When do default parameters get their values set? Dave Angel <davea@davea.name> - 2014-12-08 17:30 -0500
  Re: When do default parameters get their values set? Tim Chase <python.list@tim.thechases.com> - 2014-12-08 16:26 -0600
  Re: When do default parameters get their values set? bSneddon <w.g.sneddon@gmail.com> - 2014-12-08 15:35 -0800
  Re: When do default parameters get their values set? Terry Reedy <tjreedy@udel.edu> - 2014-12-08 20:37 -0500

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