itertools permutations python code example

Example 1: python product

#from itertools import product


def product(*args, **kwds):
    # product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
    # product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
    pools = map(tuple, args) * kwds.get('repeat', 1)
    result = [[]]
    for pool in pools:
        result = [x+[y] for x in result for y in pool]
    for prod in result:
        yield tuple(prod)

Example 2: python itertools repeat()

# How to use it:
# repeat(var, amount)

# repeat() is basically like range() but it gives an extra arg for a var

from itertools import repeat

for x in repeat("Spam? Or Eggs?", 3):
    print(x)
> "Spam? Or Eggs?"
> "Spam? Or Eggs?"
> "Spam? Or Eggs?"

Example 3: python combinations

def permutations(iterable, r=None):
    # permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
    # permutations(range(3)) --> 012 021 102 120 201 210
    pool = tuple(iterable)
    n = len(pool)
    r = n if r is None else r
    if r > n:
        return
    indices = list(range(n))
    cycles = range(n, n-r, -1)
    yield tuple(pool[i] for i in indices[:r])
    while n:
        for i in reversed(range(r)):
            cycles[i] -= 1
            if cycles[i] == 0:
                indices[i:] = indices[i+1:] + indices[i:i+1]
                cycles[i] = n - i
            else:
                j = cycles[i]
                indices[i], indices[-j] = indices[-j], indices[i]
                yield tuple(pool[i] for i in indices[:r])
                break
        else:
            return

Example 4: itertools.zip_longest fill value

from itertools import zip_longest

chars = []
correct = 'hangman'
guess = 'winger'
for c, g in zip_longest(correct, guess, fillvalue='_'):
    if c == g:
        chars.append(c)
    else:
        chars.append('_')

print(chars)
# ['_', '_', 'n', 'g', '_', '_', '_']

word = ''.join(chars)
print(word)
# __ng___