Which one is faster?

Question

Comprehension vs Generation Expression

G=[c * 4 for c in "name"] #list comprehension

G=(c * 4 for c in "name") #generator expression
G=list(G)

Answer 1

In terms of speed list comprehension is faster:

import timeit
def m1():
return [c * 4 for c in "name"]

def m2():
return list(c * 4 for c in "name")

timeit.timeit(m1, number = 100000)
0.11164118750606707
timeit.timeit(m2, number = 100000)
0.20338840264500302

This is also true for larger iterations:

def m1():
return [c * 4 for c in range(10000)]

def m2():
return list(c * 4 for c in range(10000))

timeit.timeit(m1, number = 100000)
132.59986820312798

timeit.timeit(m2, number = 100000)
188.7506580221831

That being said, for very large iterations generators have an advantage in memory usage, because while the list is created in its entirety right away, a generator will simply iterate through every element on the fly, so you can use it for virtually infinite sequences.

Answer 2

Agree with @Maya, sometimes you do not need a list but just as intermediate to get result from the list, say sum of the list values, or what ever, then you should definitely use just generator, like
sum( k for k in range(101) ), rather than
sum( [ k for k in range(101) ] )