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Super Kai (Kazuya Ito)
Super Kai (Kazuya Ito)

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itertools in Python (8)

#python #itertools #iterator #function

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*Memo:

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

*Memo:

  • The 1st argument is function(Required-Type:Callable/NoneType):
    • Don't use function=.
  • The 2nd argument is iterable(Required-Type:Iterable):
    • Don't use iterable=. 
from itertools import starmap x = starmap(lambda: None, []) x = starmap(None, []) print(x) # <itertools.starmap object at 0x000001BE9A289CF0>  print(next(x)) # StopIteration:
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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:
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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
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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
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tee() can return a tuple of the iterators which each return the elements of iterable one by one as shown below:

*Memo:

  • The 1st argument is iterable(Required-Type:Iterable):
    • Don't use iterable=.
  • The 2nd argument is n(Optional-Default:2-Type:int):
    • It's the number of iterators.
    • 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']) 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])) # StopIteration: print(next(v[1])) # StopIteration:
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from itertools import tee for x in tee('ABC'): # for x in tee(['A', 'B', 'C']):  for y in x: print(y) # A # B # C # A # B # C
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from itertools import tee for x in tee('ABC', 3): # for x in tee(['A', 'B', 'C'], 3):  for y in x: print(y) # A # B # C # A # B # C # A # B # C
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zip_longest() can return the iterator which aggregates the elements of *iterables one by one to returns a tuple of one 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 fillvalue(Optional-Default:None-Type:Any):
    • 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:
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from itertools import zip_longest v = zip_longest('ABC') v = zip_longest(['A', 'B', 'C']) print(next(v)) # ('A',) print(next(v)) # ('B',) print(next(v)) # ('C',) print(next(v)) # StopIteration:
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from itertools import zip_longest v = zip_longest('ABC', 'vwxyz') v = zip_longest(['A', 'B', 'C'], ['v', 'w', 'x', 'y', 'z']) 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:
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from itertools import zip_longest v = zip_longest('ABC', 'vwxyz', fillvalue='Abscent') v = zip_longest(['A', 'B', 'C'], ['v', 'w', 'x', 'y', 'z'], fillvalue='Abscent') print(next(v)) # ('A', 'v') print(next(v)) # ('B', 'w') print(next(v)) # ('C', 'x') print(next(v)) # ('Abscent', 'y') print(next(v)) # ('Abscent', 'z') print(next(v)) # StopIteration:
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from itertools import zip_longest for x in zip_longest('ABC', 'vwxyz', [10, 20], fillvalue='Abscent'): # for x in zip_longest(['A', 'B', 'C'], ['v', 'w', 'x', 'y', 'z'], # [10, 20], fillvalue='Abscent'):  print(x) # ('A', 'v', 10) # ('B', 'w', 20) # ('C', 'x', 'Abscent') # ('Abscent', 'y', 'Abscent') # ('Abscent', 'z', 'Abscent')
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from itertools import zip_longest for x in zip_longest('ABC', 'vwxyz', [10, 20], fillvalue='Abscent'): # for x in zip_longest(['A', 'B', 'C'], ['v', 'w', 'x', 'y', 'z'], # [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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