lambda returns lambda in python

Question

Very rarely I'll come across some code in python that uses an anonymous function which returns an anonymous function...?

Unfortunately I can't find an example on hand, but it usually takes the form like this:

g = lambda x,c: x**c lambda c: c+1

Why would someone do this? Maybe you can give an example that makes sense (I'm not sure the one I made makes any sense).

Edit: Here's an example:

swap = lambda a,x,y:(lambda f=a.__setitem__:(f(x,(a[x],a[y])),
       f(y,a[x][0]),f(x,a[x][1])))()

Answer 1

You could use such a construct to do currying:

curry = lambda f, a: lambda x: f(a, x)

You might use it like:

>>> add = lambda x, y: x + y
>>> add5 = curry(add, 5)
>>> add5(3)
8

Answer 2

It can be useful for temporary placeholders. Suppose you have a decorator factory:

@call_logger(log_arguments=True, log_return=False)
def f(a, b):
    pass

You can temporarily replace it with

call_logger = lambda *a, **kw: lambda f: f

It can also be useful if it indirectly returns a lambda:

import collections
collections.defaultdict(lambda: collections.defaultdict(lambda: collections.defaultdict(int)))

It's also useful for creating callable factories in the Python console.

And just because something is possible doesn't mean that you have to use it.