Self function

Arnaud Delobelle arnodel at googlemail.com
Mon May 4 08:29:29 CEST 2009


bearophileHUGS at lycos.com writes:

> Sometimes I rename recursive functions, or I duplicate&modify them,
> and they stop working because inside them there's one or more copy of
> their old name.
> This happens to me more than one time every year.
> So I have written this:
>
> from inspect import getframeinfo, currentframe
>
> def SOMEVERYUGLYNAME(n):
>     if n <= 1:
>         return 1
>     else:
>         self_name = getframeinfo(currentframe()).function
>         #self_name = getframeinfo(currentframe())[2] # older python
>
>         # only if it's a global function
>         #return n * globals()[self_name](n - 1)
>         return n * eval(self_name + "(%d)" % (n - 1))
> assert SOMEVERYUGLYNAME(6) == 2*3*4*5*6
>
> Are there nicer ways to do that? I don't know.
> If there aren't, then a way may be added.
> An idea-syntax:
>
> def fact(n):
>     return 1 if n <= 1 else n * inspect.self(n - 1)
>
> Or even a lambda, because you don't need the name anymore to call the
> function:
>
> fact = lambda n: 1 if n <= 1 else n * self(n - 1)
>
> (If you have two or more recursive functions that call each other this
> idea can't be used, but I think such situations are uncommon enough to
> not deserve help from the language).
>
> Bye,
> bearophile

Here's an idea:

>>> def bindfunc(f):
...     def boundf(*args, **kwargs):
...         return f(boundf, *args, **kwargs)
...     return boundf
... 
>>> @bindfunc
... def fac(self, n):
...     return 1 if n <= 1 else n * self(n - 1)
... 
>>> fac(5)
120
>>> fac = bindfunc(lambda f, n: 1 if n <= 1 else n*f(n - 1))
>>> fac(5)
120

-- 
Arnaud






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