for loops and empty iterables
Just van Rossum and I were discussing the for:else:, while:else: and try:else: syntax on the MacPythonChannel this morning (morning for me, at least). I'm not sure if this is sufficiently covered elsewhere, but here is the pattern I use to check for empty iterables:
class NoValue: """A unique placeholder, since None is sometimes used in iterables""" def doesSomethingWithIterable(iterable): x = NoValue for x in iterable: pass # something useful could go here ;) else: if x is NoValue: pass # do something because iterable was empty else: pass # do something because iterable was not empty