What are the important language features (idioms) of Python to learn early on [duplicate]

Answer 1

Here's one that can help. What's the difference between:

[ foo(x) for x in range(0, 5) ][0]

and

( foo(x) for x in range(0, 5) ).next()

answer: in the second example, foo is called only once. This may be important if foo has a side effect, or if the iterable being used to construct the list is large.