Function attributes

Steven D'Aprano steve at REMOVE-THIS-cybersource.com.au
Wed Feb 10 16:33:34 CET 2010


On Wed, 10 Feb 2010 10:08:47 -0500, John Posner wrote:

>> This won't work correctly, because old_f still tries to refer to itself
>> under the name "f", and things break very quickly.
> 
> They didn't break immediately for me -- what am I missing?:

The original function f doesn't try to refer to itself in any way. With 
no recursive call or access, it doesn't matter what f is named.

See this example  instead:


>>> def f(x):
...     if x < 0:
...             print "original"
...             return f(-x)
...     else:
...             return x+1
...
>>> f(2)
3
>>> f(-2)
original
3
>>>
>>> old_f = f
>>> def f(x):
...     if x > 0:
...             return old_f(-x)
...     else:
...             return x
...
>>> f(-1)
-1
>>> f(1)
original
original
original
original
original
original
[...]
  File "<stdin>", line 3, in f
  File "<stdin>", line 4, in f
  File "<stdin>", line 3, in f
RuntimeError: maximum recursion depth exceeded





-- 
Steven



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