Checking if iterable is empty before while loop

Question

Recently I have had to make dynamically changing lists I iterate through in the main loop. But they are empty initially, and may be empty sometimes. Here are two cases:

# The first one
iterable = []
if iterable:
    for i in iterable:
        # do sth

# and the second
iterable = []
for i in iterable:
    # do sth

I'm wondering if there is some difference in performance of these 2 cases, or the empty check is already implemented in the for loop?

Answer 1

When you iterate over a define list variable, you do not encounter any problems, have a look:

>>> iterable=[]
>>> for x in iterable:
    print(x)

>>> 

The empty check is done automatically for you.

So, it is preferable to use the second code snippet in your question, because there is no redundant if iterable: code line.