I am reading a snippet of Python code and there is one thing I can't understand. a is a list, num is an integer
a += num,
works but
a += num
won't work. Can anyone explain this to me?
First of all, it is important to note here that a += 1, works differently than a = a + 1, in this case. (a = a + 1, and a = a + (1,) are both throwing a TypeError because you can't concatenate a list and a tuple, but you you can extend a list with a tuple.)
+= calls the lists __iadd__ method, which calls list.extend and then returns the original list itself.
1, is a tuple of length one, so what you are doing is
>>> a = []
>>> a.extend((1,))
>>> a
[1]
which just looks weird because of the length one tuple. But it works just like extending a list with a tuple of any length:
>>> a.extend((2,3,4))
>>> a
[1, 2, 3, 4]