Why I wish Python had assignment in conditionals
There's a lot of times where a function wants to return more than a plain boolean; for example, validation routines often want to return some sort of explanation of the validation error (if there is one). At the same time, the most natural way to use the function is often in the flow of a conditional:
if blah(o): .... elif not validates(o): # whoops, lost the error reason
There's a variety of traditional answers to this, but I don't really
like any of them because they all obscure (to some degree) the logic
of what is going on. The right way of saying 'I am using this as a
condition but capturing its return value for later use' is an assignment
in a conditional; it is explicit and unambiguous (apart from the bit
== are too close to each other).
Python being Python, we can of course actually do this via a suitable hack:
def capture(store, res): store = res return res store = [None,] if blah(o): ... elif capture(store, validates(o)): ... use store ...
Just like the last one, I suspect that this is not going to be considered really Pythonic.
(With sufficient cleverness, you can construct a version of
that is passed
store's name and puts the result in it directly,
without needing you to make it an array and use
store. To appeal
to the Lisp crowd, call the routine