Python Language Basic use of map, itertools.imap and

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The map function is the simplest one among Python built-ins used for functional programming. map() applies a specified function to each element in an iterable:

names = ['Fred', 'Wilma', 'Barney']
Python 3.x3.0
map(len, names)  # map in Python 3.x is a class; its instances are iterable
# Out: <map object at 0x00000198B32E2CF8>

A Python 3-compatible map is included in the future_builtins module:

Python 2.x2.6
from future_builtins import map  # contains a Python 3.x compatible map()
map(len, names)                  # see below
# Out: <itertools.imap instance at 0x3eb0a20>

Alternatively, in Python 2 one can use imap from itertools to get a generator

Python 2.x2.3
map(len, names)   # map() returns a list
# Out: [4, 5, 6]

from itertools import imap
imap(len, names)  # itertools.imap() returns a generator
# Out: <itertools.imap at 0x405ea20>

The result can be explicitly converted to a list to remove the differences between Python 2 and 3:

list(map(len, names))
# Out: [4, 5, 6]

map() can be replaced by an equivalent list comprehension or generator expression:

[len(item) for item in names] # equivalent to Python 2.x map()
# Out: [4, 5, 6]

(len(item) for item in names) # equivalent to Python 3.x map()
# Out: <generator object <genexpr> at 0x00000195888D5FC0>
Mapping each value in an iterable