When should I use a Map instead of a For Loop?

Question

This is relating to the following: (In Python Code)

for i in object:
     doSomething(i)

versus

map(doSomething, object)
         


        

Answer 1

EDIT: I didn't realize that map equals itertools.imap after python 3.0. So the conclusion here may not be correct. I'll re-run the test on python 2.6 tomorrow and post result.

If doSomething is very "tiny", map can be a lot faster than for loop or a list-comprehension:

# Python 3.1.1 (r311:74483, Aug 17 2009, 17:02:12) [MSC v.1500 32 bit (Intel)] on win32

from timeit import timeit

do = lambda i: i+1

def _for():
  for i in range(1000):
    do(i)

def _map():
  map(do, range(1000))

def _list():
  [do(i) for i in range(1000)]

timeit(_for, number=10000)  # 2.5515936921388516
timeit(_map, number=10000)  # 0.010167432629884843
timeit(_list, number=10000) # 3.090125159839033

This is because map is written in C, while for loop and list-comprehension run in python virtual machine.