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Typing

Typing⚑

Since Python 3.5, type hints are supported. Note that the Python runtime does not enforce function and variable type annotations but they can be used by third party tools such as type checkers, IDEs, linters, etc.

Usage⚑

When defining a function, the syntax to specify the type of an argument and its default value, which is optional, is {arg_name}: {arg_type} = {arg_default_value}. The return type can also by specified. Let's see an example:

def greeting(name: str) -> str:
    return 'Hello ' + name

Type aliases⚑

A type alias is defined by assigning the type to the alias. For example:

import pandas as pd
import networkx as nx

## Type aliases
Series = pd.core.series.Series
DataFrame = pd.core.frame.DataFrame
Graph = nx.classes.graph.Graph

Types⚑

Common types from typing:

  • Type[Class]: Accepts instances of the Class and the Class itself.
  • Awaitable: Promise/Future.

Common problems⚑

F821 undefined name when class method return type is the class name⚑

Since the class is not defined yet, to use it as the return type that a class method returns you need to:

from __future__ import annotations