*Memo:
- My post explains a list and the list with indexing.
- My post explains list functions (1).
- My post explains list functions (2).
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']
A list can be continuously used through multiple variables as shown below:
v1 = v2 = v3 = ['a', 'b', 'c', 'd', 'e'] # Equivalent
# v1 = ['a', 'b', 'c', 'd', 'e']
v1[0] = 'X' # v2 = v1
v2[3:5] = ['Y', 'Z'] # v3 = v2
del v3[1:3]
print(v1) # ['X', 'Y', 'Z']
print(v2) # ['X', 'Y', 'Z']
print(v3) # ['X', 'Y', 'Z']
A list can be shallow-copied and deep-copied as shown below:
<Shallow copy>:
*Memo:
-
v1
andv2
refer to different outer lists and the same inner list. -
is
keyword can check ifv1
andv2
refer to the same outer and/or inner list. -
list.copy(), copy.copy(), list() and slicing can shallow-copy a list:
-
list.copy()
has no arguments.
-
import copy
v1 = ['a', 'b', ['c', 'd']]
v2 = v1.copy()
v2 = copy.copy(v1)
v2 = list(v1)
v2 = v1[:]
print(v1) # ['a', 'b', ['c', 'd']]
print(v2) # ['a', 'b', ['c', 'd']]
print(v1 is v2, v1[2] is v2[2])
# False True
v2[1] = 'X'
v2[2][0] = 'Y'
# ↓↓↓ ↓↓↓
print(v1) # ['a', 'b', ['Y', 'd']]
print(v2) # ['a', 'X', ['Y', 'd']]
# ↑↑↑ ↑↑↑
<Deep copy>:
*Memo:
-
v1
andv2
refer to different outer and inner lists. - copy.deepcopy() deep-copies a list.
-
copy.deepcopy()
should be used because it's safe, deeply copying a list whilelist.copy()
,copy.copy()
,list()
and slicing aren't safe, shallowly copying a list.
import copy
v1 = ['a', 'b', ['c', 'd']]
v2 = copy.deepcopy(v1)
print(v1) # ['a', 'b', ['c', 'd']]
print(v2) # ['a', 'b', ['c', 'd']]
print(v1 is v2, v1[2] is v2[2])
# False False
v2[1] = 'X'
v2[2][0] = 'Y'
# ↓↓↓ ↓↓↓
print(v1) # ['a', 'b', ['c', 'd']]
print(v2) # ['a', 'X', ['Y', 'd']]
# ↑↑↑ ↑↑↑
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