mapping None values to ''

Jean-Paul Calderone exarkun at divmod.com
Sun Jun 18 19:28:36 CEST 2006


On Sun, 18 Jun 2006 07:37:00 -0500, Tim Chase <python.list at tim.thechases.com> wrote:
>> i wish to map None or "None" values to "".
>> eg
>> a = None
>> b = None
>> c = "None"
>>
>> map( <something>  ,  [i for i in [a,b,c] if i in ("None",None) ])
>>
>> I can't seem to find a way to put all values to "". Can anyone help?
>> thanks
>
>I'd consider this a VeryBadIdea(tm).  However, given Python's
>introspective superpowers, it *can* be done (even if it most
>likely *shouldn't* be done).  That caveat out of the way, here goes:
>
> >>> for scope in [locals, globals]:
>...     s = scope()
>...     for vbl, value in s.items():
>...             if value == None or (type(value) == type("") and
>value == 'None'):
>...                     s[vbl] = ''
>

Hey Tim,

Actually this doesn't work for locals at all:


  >>> def f():
  ...     x = 'x'
  ...     locals()['x'] = 'y'
  ...     print x
  ... 
  >>> f()
  x
  >>> 

Locals cannot be modified through the dict returned by locals().

>
>There may be some better way to determing whether an item is a
>string than my off-the-cufff
>
>	type(value) == type("")
>

Yes.  isinstance(value, str) is the best way to do this.

Jean-Paul



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