This article shows the difference between
extend() for Python Lists.
Appends x to the end of the sequence. This means it inserts one item. In the following example we have a nested list as the third item as a consequence.
a = [1, 2] b = [3, 4] a.append(b) # a = [1, 2, [3, 4]]
Extends the list by appending elements from the iterable.
a = [1, 2] b = [3, 4] a.extend(b) # a = [1, 2, 3, 4]
For example, b could also be a tuple. This works and the resulting list would be the same. It's worth mentioning that the += operator does the same as
a = [1, 2] b = (3, 4) a += b # a = [1, 2, 3, 4]
On the other hand, the single + operator with a new assignement is not allowed for different types:
a = [1, 2] b = (3, 4) a = a + b # TypeError: can only concatenate list (not "tuple") to list