*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).
An empty iterator isn't False as shown below:
print(bool(iter([]))) # Empty iterator
# True
print(bool(iter([0]))) # iterator
print(bool(iter([iter([])]))) # iterator(Empty iterator)
# True
An iterator can be checked if a specific element is in the iterator with in keyword as shown below:
v = iter(['A', iter(['B', 'C'])])
print('A' in v)
# True
print('a' in v)
print('B' in v)
print('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)
print(['A'] in v)
print(['B'] in v)
print(['C'] in v)
print(['B', 'C'] in v)
print(['A', ['B', 'C']] in v)
# False
An iterator and one or more iterators cannot be concatenated with + and | as shown below:
v = iter([0, 1, 2]) + iter([iter([3, 4])]) + iter([iter([iter([5, 6, 7, 8])])])
# TypeError: unsupported operand type(s) for +: 'list_iterator' and
# 'list_iterator'
v = iter([0, 1, 2]) | iter([iter([3, 4])]) | iter([iter([iter([5, 6, 7, 8])])])
# TypeError: unsupported operand type(s) for |: 'list_iterator' and
# 'list_iterator'
An iterator cannot be enlarged with * and a number as shown below:
v = iter([0, 1, 2, 3, 4]) * 3
# TypeError: unsupported operand type(s) for *: 'list_iterator' and 'int'
An iterator can be iterated with a for statement as shown below:
<1D iterator>:
for x in iter([0, 1, 2, 3, 4]):
print(x)
# 0
# 1
# 2
# 3
# 4
<2D iterator>:
for x in iter([iter([0, 1, 2, 3]), iter([4, 5, 6, 7])]):
for y in x:
print(y)
# 0
# 1
# 2
# 3
# 4
# 5
# 6
# 7
<3D iterator>:
for x in iter([iter([iter([0, 1]), iter([2, 3])]),
iter([iter([4, 5]), iter([6, 7])])]):
for y in x:
for z in y:
print(z)
# 0
# 1
# 2
# 3
# 4
# 5
# 6
# 7
An iterator can be unpacked with an assignment and for statement, function and * but not with ** as shown below:
v1, v2, v3 = iter([0, 1, 2])
print(v1, v2, v3)
# 0 1 2
v1, *v2, v3 = iter([0, 1, 2, 3, 4, 5])
print(v1, v2, v3) # 0 [1, 2, 3, 4] 5
print(v1, *v2, v3) # 0 1 2 3 4 5
for v1, v2, v3 in iter([iter([0, 1, 2]), iter([3, 4, 5])]):
print(v1, v2, v3)
# 0 1 2
# 3 4 5
for v1, *v2, v3 in iter([iter([0, 1, 2, 3, 4, 5]),
iter([6, 7, 8, 9, 10, 11])]):
print(v1, v2, v3)
print(v1, *v2, v3)
# 0 [1, 2, 3, 4] 5
# 0 1 2 3 4 5
# 6 [7, 8, 9, 10] 11
# 6 7 8 9 10 11
print(*iter([0, 1]), 2, *iter([3, 4, *iter([5])]))
# 0 1 2 3 4 5
print([*iter([0, 1]), 2, *iter([3, 4, *iter([5])])])
# [0, 1, 2, 3, 4, 5]
def func(p1='a', p2='b', p3='c', p4='d', p5='e', p6='f'):
print(p1, p2, p3, p4, p5, p6)
func()
# a b c d e f
func(*iter([0, 1, 2, 3]), *iter([4, 5]))
# 0 1 2 3 4 5
def func(p1='a', p2='b', *args):
print(p1, p2, args)
print(p1, p2, *args)
print(p1, p2, ['A', 'B', *args, 'C', 'D'])
func()
# a b ()
# a b
# a b ['A', 'B', 'C', 'D']
func(*iter([0, 1, 2, 3]), *iter([4, 5]))
# 0 1 (2, 3, 4, 5)
# 0 1 2 3 4 5
# 0 1 ['A', 'B', 2, 3, 4, 5, 'C', 'D']