Question

I’ve noticed that when I’m using python, I’ll occasionally make a typographical error and have a definition that looks something like

L = [1,2,3,]

My question is, why doesn’t this cause an error?

Answer 1

It doesn’t cause an error because it is an intentional feature that trailing commas are allowed for lists and tuples.

This is especially important for tuples, because otherwise it would be difficult to define a single element tuple:

>>> (100,)   # this is a tuple because of the trailing comma
(100,)
>>> (100)    # this is just the value 100
100

It can also make it easier to reorder or add elements to long lists.