What’s the difference between plus and append in python for list manipulation? [duplicate]

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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]

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.

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