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Re: When do default parameters get their values set?

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  To: bSneddon
Copy: python-list@python.org

On 2014-12-08 14:10, bSneddon 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']):

At this point (after the "def" has completed defining the function),
the expression is evaluated and assigned to the default argument.

> beTest.cfg['def'] = "no red"
> beTest.printDef()
>
> This prints blue.      I suppose because I am changing a local copy
> of cfg dictionary.  What is the write approach here?

Well, you can bind to a default dictionary rather than an entry in
that dictionary:


  cfg = {'def': 'blue'}
  def printDef(config=cfg):
    ...
    access(config['def'])

which will make the look-up happen at run-time rather than
definition/bind-time.

  beTest.cfg['def'] = 'Red!'
  beTest.printDef()
  # should print "Red!"

-tkc

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When do default parameters get their values set? "bSneddon" <bsneddon@1:249/999.remove-cdt-this> - 2014-12-09 11:32 -0500
  Re: When do default parameters get their values set? "Chris Angelico" <chris.angelico@1:249/999.remove-cdt-this> - 2014-12-09 11:32 -0500
  Re: When do default parameters get their values set? "Dave Angel" <dave.angel@1:249/999.remove-cdt-this> - 2014-12-09 11:32 -0500
    Re: When do default parameters get their values set? Duncan Booth <duncan.booth@invalid.invalid> - 2014-12-09 21:18 +0000
      Re: When do default parameters get their values set? random832@fastmail.us - 2014-12-09 18:07 -0500
        Re: When do default parameters get their values set? Rustom Mody <rustompmody@gmail.com> - 2014-12-09 18:44 -0800
          Re: When do default parameters get their values set? random832@fastmail.us - 2014-12-10 13:38 -0500
            Re: When do default parameters get their values set? Rustom Mody <rustompmody@gmail.com> - 2014-12-10 18:18 -0800
              Re: When do default parameters get their values set? Chris Angelico <rosuav@gmail.com> - 2014-12-11 13:24 +1100
                Re: When do default parameters get their values set? Rustom Mody <rustompmody@gmail.com> - 2014-12-10 18:50 -0800
              Re: When do default parameters get their values set? Steven D'Aprano <steve@pearwood.info> - 2014-12-11 03:15 +0000
                Re: When do default parameters get their values set? Rustom Mody <rustompmody@gmail.com> - 2014-12-10 19:26 -0800
                Re: When do default parameters get their values set? Ben Finney <ben+python@benfinney.id.au> - 2014-12-11 14:49 +1100
                Re: When do default parameters get their values set? Chris Kaynor <ckaynor@zindagigames.com> - 2014-12-11 09:10 -0800
                Re: When do default parameters get their values set? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-12-12 09:51 +1100
              Re: When do default parameters get their values set? random832@fastmail.us - 2014-12-11 15:44 -0500
  Re: When do default parameters get their values set? "Tim Chase" <tim.chase@1:249/999.remove-cdt-this> - 2014-12-09 11:32 -0500

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