dict.get(key, default): conditional default evaluation

[Gustavo Niemeyer]

[...]
> I'd prefer if in the latter case A.__init__
> would not be evaluated.  Similar in spirit to
> b in (a and b) not being evaluated if a is False.

You can't change the whole evaluation logic of the language
to satisfy a minor preference for a single method. OTOH, this
behavior is quite easy to achieve:

>>> class lazydict(dict):
...   def lazyget(self, key, default=None):
...     try:
...       return self[key]
...     except KeyError:
...       if default is not None:
...         return eval(default)
...     return None
... 
>>> d = lazydict()
>>> def A():
...   print "I'm A()"
... 
>>> d.get(1, "A()")
'I'm A()'
>>> d[1] = True
>>> d.get(1, "A()")
1

-- 
Gustavo Niemeyer

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