Make your code pythonic

1-Enumerate.py

#example of bad code
for indice in xrange(0, len(l)):
    print "l[%d] = %r" % (indice, l[indice])

# ==>
#the best way to perform such operation (get indices and corresponding values) is by using enumerate

for indice, value in enumerate(l):
    print "l[%d] = %r" % (indice, value)
#since enumerate returns a list of tuples :
for i in enumerate(l):
    print "l[%d] = %r" % i

2-Generators.py

#simple range
def my_range(x, y=0):
    if y < x: # inverse if y < x
        x, y = y, x

    yield x # return the first x
    while x < y:
        x += 1
        yield x

#simple enumerate
def enumerate(i):
    for i in xrange(0, len(i)):
        yield i, i[i]

#simple xrange
def xrange(start, stop=None, step=1):
    if stop is None:
        start, stop = 0, start
    while step > 0 and start < stop or step < 0 and start > stop:
        yield start
        start += step

3-corouines.py

def cpt(x):
    n = 0
    while n <= x:
        v = (yield n)
        if v is not None:
            n = v
        else:
            n += 1

gen = cpt(20)
for i in gen:
    print i
    # we want to go from 15 to 18
    if i == 15:
        gen.send(18)

4-zip function.py

#suppose we want to iterate over 2 list l1 & l2
#ths easiest way to do is :
for i in xrange(min(len(l1), len(l2))):
    v1, v2 = l1[i], l2[i]
    # do something with v1, v2

#the easiest way to do so:
for v1, v2 in zip(l1, l2):
    # do something with v1, v2

#zip definition:
#zip(...)
    # zip(seq1 [, seq2 [...]]) -> [(seq1[0], seq2[0] ...), (...)]
    # Return a list of tuples, where each tuple contains the i-th element
    # from each of the argument sequences. The returned list is truncated
    # in length to the length of the shortest argument sequence.

#e.g
print zip(['a', 'b', 'c'], ['d', 'e', 'f']) # [('a', 'd'), ('b', 'e'), ('c', 'f')]

#python doesn't provide an unzip function but we can easily code one:
unzip = lambda l: [list(li) for li in zip(*l)]
unzip([(1, 2), (3, 4), (5, 6)]) # [[1, 3, 5], [2, 4, 6]]

5-itertools.py

# imap, ifilter, ifilterfalse
from itertools import imap, ifilter, ifilterfalse
pair = lambda n: n % 2 == 0
sqr = lambda n: n ** 2

imap(carre, xrange(10)) # Renvoie un générateur <itertools.imap object at 0x7f4ab174fc10>

for elem in imap(sqr, xrange(10)): print elem
0
1
4
9
16
25
36
49
64
81

list(ifilter(pair, xrange(10))) #[0, 2, 4, 6, 8]

list(ifilterfalse(pair, xrange(10))) #[1, 3, 5, 7, 9]

#chain
from itertools import chain
list(chain(xrange(11), xrange(15, 21), xrange(30, 46)))
#[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 16, 17, 18, 19, 20, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, #44, 45]

#takewhile & dropwhile
from itertools import takewhile, dropwhile

list(takewhile(lambda i: i < 10, xrange(20))) # takes while i < 10 : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
list(dropwhile(lambda i: i < 10, xrange(20))) # drops while i < 10 : [10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

#groupby
from itertools import groupby
l = list('aaaaabbbcddddee')
for elt, itr in groupby(l):
    print "%s : %d times" % (elt, len(list(itr)))
#a : 5 times
#b : 3 time
#c : 1 time
#d : 4 times
#e : 2 times

6-with.py

#very important use of "with" is with file management
f = open('file', 'w')
try:
    # Operations f
except Exception:
    # some problems
finally:
    # close f
    f.close()

#w can the exact same :
with open('file', 'w') as f:
    # Operations f