itertools in Python (6)

#python #itertools #iterator #function

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*Memos:

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().

itertools has the functions to create iterators.

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

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:

*Memos:

The 1st or the later arguments are *iterables(Optional-Type:iterable). *Don't use any keywords like *iterables=, iterables=, *iterable=, iterable=, etc.
The 2nd argument is repeat(Optional-Default:1-Type:int): *Memos:
- 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('ABC', repeat=1)
v = product(['A', 'B', 'C'], repeat=1)

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

from itertools import product

v = product('ABC', repeat=2)

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

from itertools import product

for x in product('ABC', 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):
    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):
    print(x)
# ('A', 'A', 'A', 'A')
# ('A', 'A', 'A', 'B')
# ('A', 'A', 'A', 'C')
# ('A', 'A', 'B', 'A')
# ('A', 'A', 'B', 'B')
# ...

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:

*Memos:

The 1st argument is iterable(Required-Type:iterable).
The 2nd argument is r(Optional-Default:None-Type:int): *Memos:
- 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=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

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

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

from itertools import permutations

for x in permutations(iterable='ABC', r=2):
    print(x)
# ('A', 'B')
# ('A', 'C')
# ('B', 'A')
# ('B', 'C')
# ('C', 'A')
# ('C', 'B')

from itertools import permutations

for x in permutations(iterable='ABC', r=3):
    print(x)
# ('A', 'B', 'C')
# ('A', 'C', 'B')
# ('B', 'A', 'C')
# ('B', 'C', 'A')
# ('C', 'A', 'B')
# ('C', 'B', 'A')

from itertools import permutations

for x in permutations(iterable='ABC', r=4):
    print(x)
# Nothing

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