Iterator in Python (2)

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*Memo:

• My post explains an iterator (1).
• My post explains an iterator (3).
• My post explains an iterator (4).
• My post explains an iterator (5).
• My post explains an iterator (6).

An iterator can be used indirectly with len() after using list(), tuple(), set() and frozenset() and directly with more_itertools.ilen() to get the length as shown below:

*Memo:

• more-itertools must be installed with pip install more-itertools.
• An iterator cannot be directly used with len() to get the length.

from copy import copy
from more_itertools import ilen

v1 = iter([0, 1, 2, 3, 4])

v2 = copy(v1)
print(len(list(v2)))
# 5

v2 = copy(v1)
print(len(tuple(v2)))
# 5

v2 = copy(v1)
print(len(set(v2)))
# 5

v2 = copy(v1)
print(len(frozenset(v2)))
# 5

v2 = copy(v1)
print(ilen(v2))
# 5

v2 = copy(v1)
print(len(v2))
# TypeError: object of type 'list_iterator' has no len()

A non-empty iterator and empty iterator are:

• True, checking them with bool() respectively.
• False, inverting their truth values with not respectively.

# Non-empty iterator
print(bool(iter([0])))
print(bool(iter([iter([])])))

# Empty iterator
print(bool(iter([])))
# True

# Non-empty iterator
print(not iter([0]))
print(not iter([iter([])]))

# Empty iterator
print(not iter([]))
# False

An iterator can be checked if a specific element is and isn't in the iterator with in and not in respectively as shown below:

v = iter(['A', iter(['B', 'C'])])

print('A' in v)
# True

print('B' in v)
print('C' in v)
print(['A'] in v)
print(['B'] in v)
print(['C'] in v)
print(['B', 'C'] in v)
print(['A', ['B', 'C']] in v)
print(iter(['A']) in v)
print(iter(['B']) in v)
print(iter(['C']) in v)
print(iter(['B', 'C']) in v)
print(iter(['A', iter(['B', 'C'])]) in v)
print(iter(['A', ['B', 'C']]) in v)
print(['A', iter(['B', 'C'])] in v)
# False

v = iter(['A', iter(['B', 'C'])])

print('A' not in v)
# False

print('B' not in v)
print('C' not in v)
print(['A'] not in v)
print(['B'] not in v)
print(['C'] not in v)
print(['B', 'C'] not in v)
print(['A', ['B', 'C']] not in v)
print(iter(['A']) not in v)
print(iter(['B']) not in v)
print(iter(['C']) not in v)
print(iter(['B', 'C']) not in v)
print(iter(['A', iter(['B', 'C'])]) not in v)
print(iter(['A', ['B', 'C']]) not in v)
print(['A', iter(['B', 'C'])] not in v)
# True

An iterator can be checked if the iterator is and isn't referred to by two variables with is and is not respectively as shown below:

v1 = iter([0, 1, 2])
v2 = iter([0, 1, 2])
v3 = v1

print(v1 is v2) # False
print(v1 is v3) # True

print(v1 is not v2) # True
print(v1 is not v3) # False

An iterator and other iterator cannot be checked if:

• all the elements in them are and aren't the equal with == and != respectively.
• the iterator is greater than other iterator with >.
• the iterator is greater than or equal to other iterator with >=.
• the iterator is less than other iterator with <.
• the iterator is less than or equal to other iterator with <=.

*Memo:

• == and != always return False and True respectively.

v = iter([0, 1, 2])

print(v == iter([0, 1, 2]))      # False
print(v == iter([2, 1, 0]))      # False
print(v == iter([0, 1, 3]))      # False
print(v == iter([0, 1, -3]))     # False
print(v == iter([0, 1]))         # False
print(v == iter([0, 3]))         # False
print(v == iter([0, -3]))        # False
print(v == iter([0, 1, 2, 3]))   # False
print(v == iter([0, 1, 3, 4]))   # False
print(v == iter([0, 1, -3, -4])) # False
print(v == iter([]))             # False

v = iter([0, 1, 2])

print(v != iter([0, 1, 2]))      # True
print(v != iter([2, 1, 0]))      # True
print(v != iter([0, 1, 3]))      # True
print(v != iter([0, 1, -3]))     # True
print(v != iter([0, 1]))         # True
print(v != iter([0, 3]))         # True
print(v != iter([0, -3]))        # True
print(v != iter([0, 1, 2, 3]))   # True
print(v != iter([0, 1, 3, 4]))   # True
print(v != iter([0, 1, -3, -4])) # True
print(v != iter([]))             # True

v = iter([0, 1, 2])

print(v > iter([0, 1, 2]))
# TypeError: '>' not supported between instances of 'list_iterator' and
# 'list_iterator'

print(v >= iter([0, 1, 2]))
# TypeError: '>=' not supported between instances of 'list_iterator' and
# 'list_iterator'

print(v < iter([0, 1, 2]))
# TypeError: '<' not supported between instances of 'list_iterator' and
# 'list_iterator'

print(v <= iter([0, 1, 2]))
# TypeError: '<=' not supported between instances of 'list_iterator' and
# 'list_iterator'

An iterator and other iterator cannot be checked if they have and don't have their common elements with bool() and & and with not and & respectively as shown below:

v = iter([0, 1, 2])

print(bool(v & iter([1, 3])))
print(not (v & iter([1, 3])))
# TypeError: unsupported operand type(s) for &: 'list_iterator' and
# 'list_iterator'