For some time now, Python developers have been able to “annotate” names with type information. With Python 3.5, type hints officially became part of the language (see PEP 484).

In Python, the most common of these data types is called the "list." The list is a zero-indexed collection of data of any type, stored linearly: the first item is at index 0, the second at index 1 ...

I've grabbed Sequence from the typing module, which includes all three Python sequence types—strings, lists and tuples. Once I do that, all of the mypy problems disappear, because all of the arguments ...