output.txt

generating 0
mapping 0
generating 1
mapping 1
generating 2
mapping 2
generating 3
mapping 3
generating 4
mapping 4
generating 5
mapping 5
generating 6
mapping 6
generating 7
mapping 7
generating 8
mapping 8
generating 9
mapping 9
['mapped 0', 'mapped 1', 'mapped 2', 'mapped 3', 'mapped 4', 'mapped 5', 'mapped 6', 'mapped 7', 'mapped 8', 'mapped 9']
--
generating 0
Traceback (most recent call last):
  File "starmap_vs_imap.py", line 20, in <module>
    print list(imap_gen)
TypeError: mapper() takes exactly 2 arguments (1 given)

starmap_vs_imap.py

from itertools import imap, starmap


def gen():
    for i in range(10):
        print "generating %s" % i
        yield (i, i*2)


def mapper(item, item_squared):
    print "mapping %s" % (item, )
    return "mapped %s" % (item)


starmap_gen = starmap(mapper, gen())
imap_gen = imap(mapper, gen())

print list(starmap_gen)
print "--"
print list(imap_gen)