[FIXED] How do you alias a type in Python?

Issue

In some (mostly functional) languages you can do something like this:

type row = list(datum)

or

type row = [datum]

So that we can build things like this:

type row = [datum]
type table = [row]
type database = [table]

Is there a way to do this in Python? You could do it using classes, but Python has quite some functional aspects so I was wondering if it could be done an easier way.

Solution

Since Python 3.5 you may use typing module.

Quoting docs, A type alias is defined by assigning the type to the alias:

# Python 3.5-3.8
from typing import List
Vector = List[float]

# Python 3.9+
Vector = list[float] # No import needed, lower case l

To learn more about enforcing types in Python you may want to get familiar with PEPs: PEP483 and PEP484.

Python historically was using duck-typing instead of strong typing and hadn't built-in way of declaring types before 3.5 release.

Answered By - Łukasz Rogalski