itertools in Python (6)

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*Memo:

• My post explains itertools about count(), cycle() and repeat().
• My post explains itertools about accumulate(), batched(), chain() and chain.from_iterable().
• My post explains itertools about compress(), filterfalse(), takewhile() and dropwhile().
• My post explains itertools about groupby() and islice().
• My post explains itertools about pairwise(), starmap(), tee() and zip_longest().
• My post explains itertools about combinations() and combinations_with_replacement().
• My post explains an iterator (1).

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itertools has the functions to create iterators.

*more-itertools has more functions by installing with pip install more-itertools.

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product() can return the iterator which does cartesian product with the elements of *iterables one by one to return a tuple of zero or more elements one by one as shown below:

*Memo:

• The 1st arguments are *iterables(Optional-Default:()-Type:Iterable):
  • Don't use any keywords like *iterables=, iterables=, etc.
• The 2nd argument is repeat(Optional-Default:1-Type:int):
  • It's the length of the returned tuple.
  • It must be 0 <= x.
  • repeat= must be used.

from itertools import product

v = product()
v = product((), repeat=1)

print(v)
# <itertools.product object at 0x000001BE99723500>

print(next(v)) # ()
print(next(v)) # StopIteration:

from itertools import product

v = product('ABC')
v = product(['A', 'B', 'C'])

print(next(v)) # ('A',)
print(next(v)) # ('B',)
print(next(v)) # ('C',)
print(next(v)) # StopIteration:

from itertools import product

for x in product('ABC', repeat=2):
# for x in product(['A', 'B', 'C'], repeat=2):
    print(x)
# ('A', 'A')
# ('A', 'B')
# ('A', 'C')
# ('B', 'A')
# ('B', 'B')
# ('B', 'C')
# ('C', 'A')
# ('C', 'B')
# ('C', 'C')

from itertools import product

for x in product('ABC', repeat=3):
# for x in product(['A', 'B', 'C'], repeat=3):
    print(x)
# ('A', 'A', 'A')
# ('A', 'A', 'B')
# ('A', 'A', 'C')
# ('A', 'B', 'A')
# ('A', 'B', 'B')
# ('A', 'B', 'C')
# ('A', 'C', 'A')
# ('A', 'C', 'B')
# ('A', 'C', 'C')
# ('B', 'A', 'A')
# ('B', 'A', 'B')
# ('B', 'A', 'C')
# ('B', 'B', 'A')
# ('B', 'B', 'B')
# ('B', 'B', 'C')
# ('B', 'C', 'A')
# ('B', 'C', 'B')
# ('B', 'C', 'C')
# ('C', 'A', 'A')
# ('C', 'A', 'B')
# ('C', 'A', 'C')
# ('C', 'B', 'A')
# ('C', 'B', 'B')
# ('C', 'B', 'C')
# ('C', 'C', 'A')
# ('C', 'C', 'B')
# ('C', 'C', 'C')

from itertools import product

for x in product('ABC', repeat=4):
# for x in product(['A', 'B', 'C'], repeat=4):
    print(x)
# ('A', 'A', 'A', 'A')
# ('A', 'A', 'A', 'B')
# ('A', 'A', 'A', 'C')
# ('A', 'A', 'B', 'A')
# ('A', 'A', 'B', 'B')
# ('A', 'A', 'B', 'C')
# ('A', 'A', 'C', 'A')
# ('A', 'A', 'C', 'B')
# ('A', 'A', 'C', 'C')
# ('A', 'B', 'A', 'A')
# ('A', 'B', 'A', 'B')
# ('A', 'B', 'A', 'C')
# ('A', 'B', 'B', 'A')
# ('A', 'B', 'B', 'B')
# ('A', 'B', 'B', 'C')
# ('A', 'B', 'C', 'A')
# ('A', 'B', 'C', 'B')
# ('A', 'B', 'C', 'C')
# ('A', 'C', 'A', 'A')
# ('A', 'C', 'A', 'B')
# ('A', 'C', 'A', 'C')
# ('A', 'C', 'B', 'A')
# ('A', 'C', 'B', 'B')
# ('A', 'C', 'B', 'C')
# ('A', 'C', 'C', 'A')
# ('A', 'C', 'C', 'B')
# ('A', 'C', 'C', 'C')
# ('B', 'A', 'A', 'A')
# ('B', 'A', 'A', 'B')
# ('B', 'A', 'A', 'C')
# ...

from itertools import product

for x in product('AB', 'C'):
# for x in product(['A', 'B'], ['C']):
    print(x)
# ('A', 'C')
# ('B', 'C')

from itertools import product

for x in product('AB', 'C', repeat=2):
# for x in product(['A', 'B'], ['C'], repeat=2):
    print(x)
# ('A', 'C', 'A', 'C')
# ('A', 'C', 'B', 'C')
# ('B', 'C', 'A', 'C')
# ('B', 'C', 'B', 'C')

from itertools import product

for x in product('AB', 'C', repeat=3):
# for x in product(['A', 'B'], ['C'], repeat=3):
    print(x)
# ('A', 'C', 'A', 'C', 'A', 'C')
# ('A', 'C', 'A', 'C', 'B', 'C')
# ('A', 'C', 'B', 'C', 'A', 'C')
# ('A', 'C', 'B', 'C', 'B', 'C')
# ('B', 'C', 'A', 'C', 'A', 'C')
# ('B', 'C', 'A', 'C', 'B', 'C')
# ('B', 'C', 'B', 'C', 'A', 'C')
# ('B', 'C', 'B', 'C', 'B', 'C')

from itertools import product

for x in product('AB', 'C', repeat=4):
# for x in product(['A', 'B'], ['C'], repeat=4):
    print(x)
# ('A', 'C', 'A', 'C', 'A', 'C', 'A', 'C')
# ('A', 'C', 'A', 'C', 'A', 'C', 'B', 'C')
# ('A', 'C', 'A', 'C', 'B', 'C', 'A', 'C')
# ('A', 'C', 'A', 'C', 'B', 'C', 'B', 'C')
# ('A', 'C', 'B', 'C', 'A', 'C', 'A', 'C')
# ('A', 'C', 'B', 'C', 'A', 'C', 'B', 'C')
# ('A', 'C', 'B', 'C', 'B', 'C', 'A', 'C')
# ('A', 'C', 'B', 'C', 'B', 'C', 'B', 'C')
# ('B', 'C', 'A', 'C', 'A', 'C', 'A', 'C')
# ('B', 'C', 'A', 'C', 'A', 'C', 'B', 'C')
# ('B', 'C', 'A', 'C', 'B', 'C', 'A', 'C')
# ('B', 'C', 'A', 'C', 'B', 'C', 'B', 'C')
# ('B', 'C', 'B', 'C', 'A', 'C', 'A', 'C')
# ('B', 'C', 'B', 'C', 'A', 'C', 'B', 'C')
# ('B', 'C', 'B', 'C', 'B', 'C', 'A', 'C')
# ('B', 'C', 'B', 'C', 'B', 'C', 'B', 'C')

permutations() can return the iterator which permutates the elements of iterable one by one to return a tuple of zero or more elements one by one as shown below:

*Memo:

• The 1st argument is iterable(Required-Type:Iterable).
• The 2nd argument is r(Optional-Default:None-Type:int or NoneType):
  • It's the length of the returned tuple.
  • If it's None or not set, the length of iterable is used.
  • It must be 0 <= x.

from itertools import permutations

v = permutations(iterable='')
v = permutations(iterable='', r=None)
v = permutations(iterable='', r=0)
v = permutations(iterable=[])

print(v)
# <itertools.permutations object at 0x000001BE9908AE30>

print(next(v)) # ()
print(next(v)) # StopIteration:

from itertools import permutations

v = permutations(iterable='A')
v = permutations(iterable='A', r=1)
v = permutations(iterable=['A'])

print(next(v)) # ('A',)
print(next(v)) # StopIteration:

from itertools import permutations

v = permutations(iterable='AB')
v = permutations(iterable='AB', r=2)
v = permutations(iterable=['A', 'B'])

print(next(v)) # ('A', 'B')
print(next(v)) # ('B', 'A')
print(next(v)) # StopIteration:

from itertools import permutations

v = permutations(iterable='ABC')
v = permutations(iterable='ABC', r=3)
v = permutations(iterable=['A', 'B', 'C'])

print(next(v)) # ('A', 'B', 'C')
print(next(v)) # ('A', 'C', 'B')
print(next(v)) # ('B', 'A', 'C')
print(next(v)) # ('B', 'C', 'A')
print(next(v)) # ('C', 'A', 'B')
print(next(v)) # ('C', 'B', 'A')
print(next(v)) # StopIteration:

from itertools import permutations

for x in permutations(iterable='ABCD'):
# for x in permutations(iterable='ABCD', r=4):
# for x in permutations(iterable=['A', 'B', 'C', 'D']):
    print(x)
# ('A', 'B', 'C', 'D')
# ('A', 'B', 'D', 'C')
# ('A', 'C', 'B', 'D')
# ('A', 'C', 'D', 'B')
# ('A', 'D', 'B', 'C')
# ('A', 'D', 'C', 'B')
# ('B', 'A', 'C', 'D')
# ('B', 'A', 'D', 'C')
# ('B', 'C', 'A', 'D')
# ('B', 'C', 'D', 'A')
# ('B', 'D', 'A', 'C')
# ('B', 'D', 'C', 'A')
# ('C', 'A', 'B', 'D')
# ('C', 'A', 'D', 'B')
# ('C', 'B', 'A', 'D')
# ('C', 'B', 'D', 'A')
# ('C', 'D', 'A', 'B')
# ('C', 'D', 'B', 'A')
# ('D', 'A', 'B', 'C')
# ('D', 'A', 'C', 'B')
# ('D', 'B', 'A', 'C')
# ('D', 'B', 'C', 'A')
# ('D', 'C', 'A', 'B')
# ('D', 'C', 'B', 'A')

from itertools import permutations

for x in permutations(iterable='ABCD', r=3):
# for x in permutations(iterable=['A', 'B', 'C', 'D'], r=3):
    print(x)
# ('A', 'B', 'C')
# ('A', 'B', 'D')
# ('A', 'C', 'B')
# ('A', 'C', 'D')
# ('A', 'D', 'B')
# ('A', 'D', 'C')
# ('B', 'A', 'C')
# ('B', 'A', 'D')
# ('B', 'C', 'A')
# ('B', 'C', 'D')
# ('B', 'D', 'A')
# ('B', 'D', 'C')
# ('C', 'A', 'B')
# ('C', 'A', 'D')
# ('C', 'B', 'A')
# ('C', 'B', 'D')
# ('C', 'D', 'A')
# ('C', 'D', 'B')
# ('D', 'A', 'B')
# ('D', 'A', 'C')
# ('D', 'B', 'A')
# ('D', 'B', 'C')
# ('D', 'C', 'A')
# ('D', 'C', 'B')

from itertools import permutations

for x in permutations(iterable='ABCD', r=2):
# for x in permutations(iterable=['A', 'B', 'C', 'D'], r=2):
    print(x)
# ('A', 'B')
# ('A', 'C')
# ('A', 'D')
# ('B', 'A')
# ('B', 'C')
# ('B', 'D')
# ('C', 'A')
# ('C', 'B')
# ('C', 'D')
# ('D', 'A')
# ('D', 'B')
# ('D', 'C')

from itertools import permutations

for x in permutations(iterable='ABCD', r=1):
# for x in permutations(iterable=['A', 'B', 'C', 'D'], r=1):
    print(x)
# ('A',)
# ('B',)
# ('C',)
# ('D',)

from itertools import permutations

for x in permutations(iterable='ABCD', r=0):
# for x in permutations(iterable=['A', 'B', 'C', 'D'], r=0):
    print(x)
# ()

from itertools import permutations

for x in permutations(iterable='ABCD', r=5):
# for x in permutations(iterable=['A', 'B', 'C', 'D'], r=5):
    print(x)
# Nothing