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Groups > comp.lang.python > #57117

Re: skipping __init__ and using exploiting a class member instead

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On 10/19/13 5:44 PM, Peter Cacioppi wrote:
> Is the following considered poor Python form?
>
> class Foo (object) :
>      _lazy = None
>      def foo(self, x) :
>          _lazy = _lazy or self.get_something(x)
>      def get_something(self, x) :
>          # doesn't really matter
>
> I like this idiom for certain situations, just wondering if it will raise the hackles of other Pythonistas.
>
> I use this idiom sparingly, but sometimes it just fits the task at hand, I hear Guidos voice saying "use the Force" in my ear, etc.

You present this as a choice between __init__ or a class attribute, but 
those two things are very different.  Is your intent to have an instance 
attribute, or a class attribute?  Lazily populated instance attributes 
are fine, I would do it like this:

class Foo(object):
     def __init__(self):
         self._lazy = None

     def foo(self, x):
         if self._lazy is None:
             self._lazy = self.get_something(x)
         ...

--Ned.

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skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-19 14:44 -0700
  Re: skipping __init__ and using exploiting a class member instead Ned Batchelder <ned@nedbatchelder.com> - 2013-10-19 17:55 -0400
  Re: skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-19 15:11 -0700
  Re: skipping __init__ and using exploiting a class member instead Robert Kern <robert.kern@gmail.com> - 2013-10-19 23:18 +0100
  Re: skipping __init__ and using exploiting a class member instead Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-19 22:30 +0000
  Re: skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-19 17:07 -0700
  Re: skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-19 17:42 -0700
    Re: skipping __init__ and using exploiting a class member instead Ned Batchelder <ned@nedbatchelder.com> - 2013-10-19 21:13 -0400
    Detecting whether a value was passed for a parameter (was: skipping __init__ and using exploiting a class member instead) Ben Finney <ben+python@benfinney.id.au> - 2013-10-20 22:50 +1100
  Re: skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-20 00:09 -0700
    Re: skipping __init__ and using exploiting a class member instead Roy Smith <roy@panix.com> - 2013-10-20 08:55 -0400
    Re: skipping __init__ and using exploiting a class member instead Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-10-20 14:16 +0100
  Re: skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-20 01:46 -0700
  Re: skipping __init__ and using exploiting a class member instead Devin Jeanpierre <jeanpierreda@gmail.com> - 2013-10-20 07:27 -0700
  Re: skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-20 10:57 -0700
    Re: skipping __init__ and using exploiting a class member instead Roy Smith <roy@panix.com> - 2013-10-20 16:44 -0400
    Re: skipping __init__ and using exploiting a class member instead Chris Angelico <rosuav@gmail.com> - 2013-10-21 07:57 +1100
      Re: skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-20 14:34 -0700
        Re: skipping __init__ and using exploiting a class member instead Roy Smith <roy@panix.com> - 2013-10-20 18:31 -0400
          Re: skipping __init__ and using exploiting a class member instead Ben Finney <ben+python@benfinney.id.au> - 2013-10-21 10:55 +1100
            Re: skipping __init__ and using exploiting a class member instead Neil Cerutti <neilc@norwich.edu> - 2013-10-21 18:47 +0000
  Re: skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-20 21:30 -0700
  Re: skipping __init__ and using exploiting a class member instead Peter Cacioppi <peter.cacioppi@gmail.com> - 2013-10-20 21:31 -0700
    Re: skipping __init__ and using exploiting a class member instead feedthetroll@gmx.de - 2013-10-21 00:16 -0700

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