1. Use the + plus sign
The + plus sign is adding two list lists to return a new list object, which consumes extra memory.
#!/usr/bin/env python
# -*- coding:utf-8 -*-
if __name__ == '__main__':
a = [1, 2, 3]
b = [4, 5, 6]
c = a + b
print(c)
Output:
[1, 2, 3, 4, 5, 6]
Process finished with exit code 0
2. Using the append() method
The append() method adds a new object to the end of the list, which has no return value but modifies the original list.
Syntax: (obj)
Parameters: obj - object to add to the end of the list.
#!/usr/bin/env python
# -*- coding:utf-8 -*-
if __name__ == '__main__':
a = [1, 2, 3]
b = [4, 5, 6]
(b)
print(a)
Output:
[1, 2, 3, [4, 5, 6]]
Process finished with exit code 0
3. Use the extend() method
The extend() method extends the original list with a new list, adding the object iteration to the back of the list, and only supports data from iterable objects. （Iterable objects: objects that can be iterated over with a for loop are iterable objects, such as strings, lists, tuples, dictionaries, collections, etc.)
This method has no return value, but adds new list contents to an already existing list.
Syntax: (seq)
Parameters: seq - list of elements.
#!/usr/bin/env python
# -*- coding:utf-8 -*-
if __name__ == '__main__':
a = [1, 2, 3]
b = [4, 5, 6]
(b)
print(a)
Output:
[1, 2, 3, 4, 5, 6]
Process finished with exit code 0
4. Difficulties
#!/usr/bin/env python
# -*- coding:utf-8 -*-
if __name__ == '__main__':
a = [1, 2, 3]
c = []
(a)
print(c)
(4)
print(c)
Output:
[[1, 2, 3]]
[[1, 2, 3, 4]]
Process finished with exit code 0
You can see that after changing the a list, the c list has also changed.
The reason for this phenomenon is that when the list list is appended using the append() method, it is actually caused by a shallow copy.
Solution: You can use () for deep copy.
#!/usr/bin/env python
# -*- coding:utf-8 -*-
import copy
if __name__ == '__main__':
a = [1, 2, 3]
c = []
((a))
print(c)
(4)
print(c)
Output:
[[1, 2, 3]]
[[1, 2, 3]]Process finished with exit code 0
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