Would Anonymous Functions Help in Learning Programming/Python?

Steven D'Aprano steve at REMOVE-THIS-cybersource.com.au
Sun Sep 23 02:02:52 CEST 2007


On Sat, 22 Sep 2007 14:09:13 -0700, Paul Rubin wrote:

>> Nevertheless, def is never a real anonymous function constructor.
> 
> Well, def constructs a function with a name, but the function can stay
> around after the name goes away, after which I'd say the function is
> nameless.  One could otherwise say that (lambda x: x+x) is not anonymous
> either, since id(lambda ...) is a unique label stuck to it like a
> __name__.

If you want to be tediously pedantic, lambda doesn't construct anonymous 
functions either: you can bind them to a name, and whether you do or not, 
they have a name.

>>> f = lambda: 3
>>> f.__name__
'<lambda>'

It's just that all functions created by lambda share the same name.

If you really want an anonymous function...

>>> def foo():
...     return 3
...
>>> foo.__name__ = ''
>>> foo
<function  at 0x97a26bc>


I know, I know, I'm being tediously pedantic... and that's not what the 
anonymity of lambda refers to. What it actually means is that the lambda 
doesn't create a name in a namespace. In that regard, calling a factory 
function is also anonymous, because the function isn't added to the 
calling code's namespace.

Or, to put it another way...

def factory():
    def foo():
        return 3
    return foo


Within factory(), foo() is not an anonymous function, because 'foo' is in 
the local namespace. But the result of factory() is anonymous in the same 
sense that lambda is: although the function object has a attribute 
__name__ set to 'foo', calling factory() doesn't modify the caller's 
namespace (unless you assign the result to a name).


-- 
Steven.



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