itertools in Python (7)

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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 product() and permutations().
• 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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combinations() can return the iterator which uniquely combines 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(Required-Type:int):
  • It's the length of the returned tuple.
  • It must be 0 <= x.

from itertools import combinations

v = combinations(iterable='', r=0)
v = combinations(iterable=[], r=0)

print(v)
# <itertools.combinations object at 0x0000026906D95CB0>

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

from itertools import combinations

v = combinations(iterable='ABCD', r=1)
v = combinations(iterable=['A', 'B', 'C', 'D'], r=1)

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

from itertools import combinations

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

from itertools import combinations

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

from itertools import combinations

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

from itertools import combinations

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

combinations_with_replacement() can return the iterator which non-uniquely combines 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(Required-Type:int):
  • It's the length of the returned tuple.
  • It must be 0 <= x.

from itertools import combinations_with_replacement

v = combinations_with_replacement(iterable='', r=0)
v = combinations_with_replacement(iterable=[], r=0)

print(v)
# <itertools.combinations_with_replacement object at 0x0000026906DAAED0>

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

from itertools import combinations_with_replacement

v = combinations_with_replacement(iterable='ABCD', r=1)
v = combinations_with_replacement(iterable=['A', 'B', 'C', 'D'], r=1)

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

from itertools import combinations_with_replacement

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

from itertools import combinations_with_replacement

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

from itertools import combinations_with_replacement

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