*Memo:
- My post explains a list (1).
- My post explains a list (2).
- My post explains a list (4).
- My post explains a list (5).
- My post explains a list (6).
A list can be iterated with a for statement as shown below:
<1D list>:
for x in [0, 1, 2, 3, 4]:
print(x)
# 0
# 1
# 2
# 3
# 4
<2D list>:
for x in [[0, 1, 2, 3], [4, 5, 6, 7]]:
for y in x:
print(y)
# 0
# 1
# 2
# 3
# 4
# 5
# 6
# 7
<3D list>:
for x in [[[0, 1], [2, 3]], [[4, 5], [6, 7]]]:
for y in x:
for z in y:
print(z)
# 0
# 1
# 2
# 3
# 4
# 5
# 6
# 7
A list can be unpacked with an assignment and for statement, function and * but not with ** as shown below:
v1, v2, v3 = [0, 1, 2]
print(v1, v2, v3)
# 0 1 2
v1, *v2, v3 = [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 [[0, 1, 2], [3, 4, 5]]:
print(v1, v2, v3)
# 0 1 2
# 3 4 5
for v1, *v2, v3 in [[0, 1, 2, 3, 4, 5], [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(*[0, 1], 2, *[3, 4, *[5]])
# 0 1 2 3 4 5
print([*[0, 1], 2, *[3, 4, *[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(*[0, 1, 2, 3], *[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 Nothing
# a b ['A', 'B', 'C', 'D']
func(*[0, 1, 2, 3], *[4, 5])
# 0 1 (2, 3, 4, 5)
# 0 1 2 3 4 5
# 0 1 ['A', 'B', 2, 3, 4, 5, 'C', 'D']
list() can create a list with or without an iterable as shown below:
*Memo:
- The 1st argument is
iterable(Optional-Default:()-Type:Iterable):- Don't use
iterable=.
- Don't use
# Empty list
print(list())
print(list(()))
# []
print(list([0, 1, 2, 3, 4])) # list
print(list((0, 1, 2, 3, 4))) # tuple
print(list({0, 1, 2, 3, 4})) # set
print(list(frozenset([0, 1, 2, 3, 4]))) # frozenset
print(list(iter([0, 1, 2, 3, 4]))) # iterator
print(list(range(5))) # range
# [0, 1, 2, 3, 4]
print(list({'name': 'John', 'age': 36})) # dict
print(list({'name': 'John', 'age': 36}.keys())) # dict.keys()
# ['name', 'age']
print(list({'name': 'John', 'age': 36}.values())) # dict.values()
# ['John', 36]
print(list({'name': 'John', 'age': 36}.items())) # dict.items()
# [('name', 'John'), ('age', 36)]
print(list('Hello')) # str
# ['H', 'e', 'l', 'l', 'o']
print(list(b'Hello')) # bytes
print(list(bytearray(b'Hello'))) # bytearray
# [72, 101, 108, 108, 111]
A list comprehension can create a list as shown below:
<1D list>:
sample = [0, 1, 2, 3, 4, 5, 6, 7]
v = [x**2 for x in sample]
print(v)
# [0, 1, 4, 9, 16, 25, 36, 49]
<2D list>:
sample = [[0, 1, 2, 3], [4, 5, 6, 7]]
v = [[y**2 for y in x] for x in sample]
print(v)
# [[0, 1, 4, 9], [16, 25, 36, 49]]
<3D list>:
sample = [[[0, 1], [2, 3]], [[4, 5], [6, 7]]]
v = [[[z**2 for z in y] for y in x] for x in sample]
print(v)
# [[[0, 1], [4, 9]], [[16, 25], [36, 49]]]
Be careful, a big list gets MemoryError as shown below:
v = [0, 1, 2, 3, 4] * 1000000000
# MemoryError
v = range(1000000000)
print(list(v))
# MemoryError
v = [x for x in range(1000000000)]
# MemoryError
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