itertools in Python (5)

#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 product() and permutations().
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.

pairwise() can return the iterator which returns a tuple of the two elements of iterable one by one as shown below:

*Memos:

The 1st argument is iterable(Required-Type:iterable).
Don't use iterable=.

from itertools import pairwise

v = pairwise('ABCD')
v = pairwise(['A', 'B', 'C', 'D'])

print(v)
# <itertools.pairwise object at 0x000001BE9A1ABF70>

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

from itertools import pairwise

for x in pairwise('ABCD'):
    print(x)
# ('A', 'B')
# ('B', 'C')
# ('C', 'D')

starmap() can return the iterator which does function with the zero or more elements of iterable one by one to return the result one by one as shown below:

*Memos:

The 1st argument is function(Required-Type:callable). *Don't use function=.
The 2nd argument is iterable(Required-Type:iterable). *Don't use iterable=.

from itertools import starmap

x = starmap(lambda: None, [])

print(x)
# <itertools.starmap object at 0x000001BE9A289CF0>

print(next(x)) # StopIteration:

from itertools import starmap
from operator import add

x = starmap(lambda a, b: a+b, [(2, 5), (3, 2), (10, 3)])
x = starmap(add, [(2, 5), (3, 2), (10, 3)])

print(next(x)) # 7
print(next(x)) # 5
print(next(x)) # 13
print(next(x)) # StopIteration:

from itertools import starmap
from operator import add

for x in starmap(lambda a, b: a+b, [(2, 5), (3, 2), (10, 3)]):
    print(x)
# 7
# 5
# 13

from itertools import starmap
from operator import mul

for x in starmap(lambda a, b: a*b, [(2, 5), (3, 2), (10, 3)]):
# for x in starmap(mul, [(2, 5), (3, 2), (10, 3)]):
    print(x)
# 10
# 6
# 30

from itertools import starmap

for x in starmap(lambda a, b: a**b, [(2, 5), (3, 2), (10, 3)]):
# for x in starmap(pow, [(2, 5), (3, 2), (10, 3)]):
    print(x)
# 32
# 9
# 1000

tee() can return the zero or more iterators in a tuple which create the zero or more copies of iterable to return the element one by one as shown below:

*Memos:

The 1st argument is iterable(Required-Type:iterable). *Don't use iterable=.
The 2nd argument is n(Optional-Default:2-Type:int): *Memos:
- It's the number of the copies of iterable.
- It must be 0 <= x.
- Don't use n=.

from itertools import tee

v = tee('ABC')
v = tee('ABC', 2)
v = tee(['A', 'B', 'C'])
v = tee(['A', 'B', 'C'], 2)

print(v)
# (<itertools._tee object at 0x000001BE99D6E3C0>,
#  <itertools._tee object at 0x000001BE99F85440>)

print(next(v[0])) # A
print(next(v[0])) # B
print(next(v[0])) # C
print(next(v[1])) # A
print(next(v[1])) # B
print(next(v[1])) # C

print(next(v[0]))
print(next(v[1]))
# StopIteration:

from itertools import tee

for x in tee('ABC'):
    for y in x:
        print(y)
# A
# B
# C
# A
# B
# C

from itertools import tee

for x in tee('ABC', 3):
    for y in x:
        print(y)
# A
# B
# C
# A
# B
# C
# A
# B
# C

zip_longest() can return the iterator which creates and returns a tuple of one or more elements one by one by zipping *iterables 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 fillvalue(Optional-Default:None-Type:object): *Memos:
- It's the value to fill the zero or more missing elements of a returned tuple.
- fillvalue= must be used.

from itertools import zip_longest

v = zip_longest()
v = zip_longest(fillvalue=None)

print(v)
# <itertools.zip_longest object at 0x000001BE99F29FD0>

print(next(v)) # StopIteration:

from itertools import zip_longest

v = zip_longest('ABC')
v = zip_longest('ABC', fillvalue=None)
v = zip_longest(['A', 'B', 'C'])
v = zip_longest(['A', 'B', 'C'], fillvalue=None)

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

from itertools import zip_longest

v = zip_longest('ABC', 'vwxyz', fillvalue=None)

print(next(v)) # ('A', 'v')
print(next(v)) # ('B', 'w')
print(next(v)) # ('C', 'x')
print(next(v)) # (None, 'y')
print(next(v)) # (None, 'z')
print(next(v)) # StopIteration:

from itertools import zip_longest

v = zip_longest('ABC', 'vwxyz', [10, 20], fillvalue='Abscent')

print(next(v)) # ('A', 'v', 10)
print(next(v)) # ('B', 'w', 20)
print(next(v)) # ('C', 'x', 'Abscent')
print(next(v)) # ('Abscent', 'y', 'Abscent')
print(next(v)) # ('Abscent', 'z', 'Abscent')
print(next(v)) # StopIteration:

from itertools import zip_longest

for x in zip_longest('ABC', 'vwxyz', [10, 20], fillvalue='Abscent'):
    print(x)
# ('A', 'v', 10)
# ('B', 'w', 20)
# ('C', 'x', 'Abscent')
# ('Abscent', 'y', 'Abscent')
# ('Abscent', 'z', 'Abscent')

from itertools import zip_longest

for x in zip_longest('ABC', 'vwxyz', [10, 20], fillvalue='Abscent'):
    for y in x:
        print(y)
# A
# v
# 10
# B
# w
# 20
# C
# x
# Abscent
# Abscent
# y
# Abscent
# Abscent
# z
# Abscent

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