Question

In PHP there a function called isset() to check if something (like an array index) exists and has a value. How about Python?

I need to use this on arrays because I get “IndexError: list index out of range” sometimes.

I guess I could use try/catching, but that’s a last resort.

Answer 1

Look before you leap (LBYL):

if idx < len(array):
    array[idx]
else:
    # handle this

Easier to ask forgiveness than permission (EAFP):

try:
    array[idx]
except IndexError:
    # handle this

In Python, EAFP seems to be the popular and preferred style. It is generally more reliable, and avoids an entire class of bugs (time of check vs. time of use). All other things being equal, the try/except version is recommended – don’t see it as a "last resort".

This excerpt is from the official docs linked above, endorsing using try/except for flow control:

This common Python coding style assumes the existence of valid keys or attributes and catches exceptions if the assumption proves false. This clean and fast style is characterized by the presence of many try and except statements.