问题
There are 2 ways to merge lists together in Python:
['a', 'b', 'c'] + ['x', 'y', 'z']['a', 'b', 'c'].extend(['x', 'y', 'z'])
What's the difference between the 2 methods?
What's the more Pythonic way of concatenating more than 2 lists?
['a', 'b', 'c'] + [1, 2, 3] + ['x', 'y', 'z']
gucci_list = ['a', 'b', 'c']
gucci_list.extend([1, 2, 3])
gucci_list.extend(['x', 'y', 'z'])
How about combining both?
['a', 'b', 'c'].extend([1, 2, 3] + ['x', 'y', 'z'])
回答1:
The first statement creates a new list out of two anonymous lists and stores it in the variable new_list:
new_list = ['a', 'b', 'c'] + ['x', 'y', 'z']
#['a', 'b', 'c', 'x', 'y', 'z']
The second statement creates an anonymous list ['a','b','c'] and appends another anonymous list to its end (now, the first list is ['a', 'b', 'c', 'x', 'y', 'z']). However, the list is still anonymous and cannot be accessed in the future. Since the method extend returns nothing, the value of the variable after the assignment is None.
new_list = ['a', 'b', 'c'].extend(['x', 'y', 'z'])
#None
The second statement can be made useful by first naming the list and then altering it:
old_list = ['a', 'b', 'c']
old_list.extend(['x', 'y', 'z']) # Now, the old list is a new list
回答2:
['a', 'b', 'c'] + ['x', 'y', 'z'] creates a new list.
['a', 'b', 'c'].extend(['x', 'y', 'z']) modifies the first list by adding the second list to it. Since the first list is not referenced by a variable, the resulting list wont be accessible anymore
回答3:
First one creates a new array from the two. Second one mutates the original list.
来源：https://stackoverflow.com/questions/51811937/whats-the-difference-between-a-b-and-a-extendb