itertools in Python (4)

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*Memo:

• My post explains itertools.

chain() and chain.from_iterable() can return the iterator which returns the elements of chained *iterables and iterable respectively one by one as shown below:

*Memo for chain():

• The 1st arguments are *iterables(Optional-Default:()-Type:Iterable):
  • Don't use any keywords like *iterables=, iterables=, etc.

*Memo for chain.from_iterable():

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

from itertools import chain

v = chain()
v = chain('')
v = chain('', '')
v = chain([])
v = chain([], [])
v = chain.from_iterable('')
v = chain.from_iterable([])

print(v)
# <itertools.chain object at 0x0000026906CEAD70>

print(next(v))
# StopIteration:

from itertools import chain

v = chain('ABCDEF')
v = chain('ABC', 'DE', 'F')
v = chain(['A', 'B', 'C', 'D', 'E', 'F'])
v = chain(['A', 'B', 'C'], ['D', 'E'], ['F'])
v = chain.from_iterable('ABCDEF')
v = chain.from_iterable(['A', 'B', 'C', 'D', 'E', 'F'])

print(next(v)) # A
print(next(v)) # B
print(next(v)) # C
print(next(v)) # D
print(next(v)) # E
print(next(v)) # F
print(next(v)) # StopIteration:

from itertools import chain

for x in chain('ABCDEF'):
# for x in chain('ABC', 'DE', 'F'):
# for x in chain(['A', 'B', 'C', 'D', 'E', 'F']):
# for x in chain(['A', 'B', 'C'], ['D', 'E'], ['F']):
# for x in chain.from_iterable('ABCDEF'):
# for x in chain.from_iterable(['A', 'B', 'C', 'D', 'E', 'F']):
    print(x)
# A
# B
# C
# D
# E
# F

compress() can return the iterator which returns the elements of data one by one if the corresponding elements of selectors are True as shown below:

*Memo:

• The 1st argument is data(Required-Type:Iterable).
• The 2nd argument is selectors(Required-Type:Iterable):
  • It selects elements from data.

from itertools import compress

v = compress(data='', selectors=[])
v = compress(data=[], selectors=[])

print(v)
# <itertools.compress object at 0x0000026905F8CF10>

print(next(v))
# StopIteration:

from itertools import compress

v = compress(data='ABCDE', selectors=[1, 0, 1, 1, 0])
v = compress(data=['A', 'B', 'C', 'D', 'E'], selectors=[1, 0, 1, 1, 0])

print(next(v)) # A
print(next(v)) # C
print(next(v)) # D
print(next(v)) # StopIteration:

from itertools import compress

for x in compress(data='ABCDE', selectors=[1, 0, 1, 1, 0]):
# for x in compress(data=['A', 'B', 'C', 'D', 'E'],
#                   selectors=[1, 0, 1, 1, 0]):
    print(x)
# A
# C
# D

from itertools import compress

for x in compress(data='ABCDE', selectors=[1, 0, 1, 1, 0, 1, 1, 1]):
# for x in compress(data=['A', 'B', 'C', 'D', 'E'],
#                   selectors=[1, 0, 1, 1, 0, 1, 1, 1]):
    print(x)
# A
# C
# D

from itertools import compress

for x in compress(data='ABCDE', selectors=[1, 0, 1]):
# for x in compress(data=['A', 'B', 'C', 'D', 'E'], selectors=[1, 0, 1]):
    print(x)
# A
# C