可能重复:Python append() vs. + 运算符在列表中，为什么这些会给出不同的结果?

在 Python 中用于列表操作的+"和附加"之间的实际区别是什么?

What is the actual difference between "+" and "append" for list manipulation in Python?

推荐答案

有两个主要区别.首先是 + 在含义上更接近于 extend 而不是 append:

There are two major differences. The first is that + is closer in meaning to extend than to append:

>>> a = [1, 2, 3]
>>> a + 4
Traceback (most recent call last):
  File "<pyshell#13>", line 1, in <module>
    a + 4
TypeError: can only concatenate list (not "int") to list
>>> a + [4]
[1, 2, 3, 4]
>>> a.append([4])
>>> a
[1, 2, 3, [4]]
>>> a.extend([4])
>>> a
[1, 2, 3, [4], 4]

另一个更突出的区别是方法就地工作:extend 实际上类似于 += - 事实上，它的行为与+= 除了它可以接受任何可迭代的，而 += 只能接受另一个列表.

The other, more prominent, difference is that the methods work in-place: extend is actually like += - in fact, it has exactly the same behavior as += except that it can accept any iterable, while += can only take another list.