if does not evaluate

[Skip Montanaro]

    Jim> lambda seem to work for very simple things but not for anything
    Jim> substantial.

Right.  Like Terry said, for anything more substantial use a named function.
Lambda was never intended to be a replacement for def, and Python is
fundamentally not a functional language (in the Haskell/Lisp sense of the
term), so powerful anonymous functions are generally not needed.  In fact,
as list comprehensions and generator expressions take root, lambda's use
dwindles.

Skip