See exactly what a function has returned

[Brad Tilley]

Peter Grayson wrote:
> This function does not do what you are expecting; type(function) does
> not return the type that function returns, it returns the type of the
> object passed in.
> 
> def foo():
>   return 42
> 
> 
>>>>print foo
> 
> <function foo at 0xf6f888ec>
> 
>>>>print type(foo)
> 
> <type 'function'>
> 
> Because Python is a dynamically typed language, it is not possible for
> the interpreter to know what type of object a function returns without
> executing it. In fact, it is possible for a function to return
> different kinds of things. For example:
> 
> def bar(x):
>   if x == 0:
>     return 42
>   elif x== 1:
>     return "Forty-two"
>   else:
>     return None
> 
> In a statically typed language, like C, we neccessarily know what type
> of thing is returned and we know it at compile-time. In Python, the
> type of the returned object is only bound at run-time. In practice,
> this means that we usually have to "just know" what a function returns
> by knowing the intended semantics of the function. That said, you
> could write a function like this that tells you about the return type
> of a function for a given invocation of that function ...
> 
> def characterize(f, *args):
>   r = f(*args)
>   print type(r)
> 
> 
>>>>characterize(bar, 0)
> 
> <type 'int'>
> 
>>>>characterize(bar, 1)
> 
> <type 'str'>
> 
>>>>characterize(bar, 2)
> 
> <type 'NoneType'>
> 
> Hope this helps.
> 
> Pete

Yes, it was very helpful. Thanks Pete.