If you give something a name, yet still only use it once, what's the point? It is just semantic clutter to do that (unless, of course, you can't use multiline lambdas...).
(See point-free style.)
def doSomething():
def doSomethingElse():
# Code goes here.
pass
eggs = filter(doSomethingElse, spam)
for cheese in eggs:
# Do something.
pass