Iterator in Python (10)
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*Memos:
* My post explains an iterator (1).
* My post explains an iterator (2).
* My post explains a generator.
* My post explains a class-based iterator with __iter__() and/or __next__().
* 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().
## _itertools has the functions to create iterators._
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>
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')
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')
