In Python, is it better to use list comprehensions or for-each loops?

Question

Which of the following is better to use and why?

Method 1:

for k, v in os.environ.items():
       print \"%s=%s\" % (k, v)

Method 2

Answer 1

The particular code examples you have chosen do not demonstrate any advantage of the list comprehension, because it is being (mis-)used for the trivial task of printing. In this simple case I would choose the simple for loop.

In many other cases, you will want to supply an actual list to another function or method, and the list comprehension is the easiest and most readable way to do that.

An example which would clearly show the superiority of the list comp could be made by replacing the print example with one involving creating another actual list, by appending to one on each iteration of the for loop:

L = []
for x in range(10):
    L.append(x**2)

Gives the same L as:

L = [x**2 for x in range(10)]