Which is faster and why? Is there a noticeable difference?
""" my_list=[1,2,3...N] """
for i in my_list:
do something
or
for i in range(1,N):
do something
It seems to me that in the second case the range function would be called N times which might be slower but I don't know how the in operator really works.
>>> t = timeit.Timer("""for i in range(3):
... pass""")
>>> t.timeit(1)
2.199320988438558e-06
as apposed to:
>>> t = timeit.Timer("""list_a=[0,1,2]
... for i in list_a:
... pass""")
>>> t.timeit(1)
4.398641522129765e-06
You can see the time differences between these operations. Besides, you should be aware that in python 2 it is more advisable using xrange instead of range if you don't need all these values at the same time (like simple iteration), since it generates a value at each iteration, which could save lots of memory and sometimes even CPU (in more complicated cases).
for more information: https://wiki.python.org/moin/Generators
rangefunction does not get called N times. If you are using Python 3.x the second method is a bit faster and more memory efficient sincerangedoes not construct the whole list in advance. For Python 2.x you can usexrangefor the same effect.