Coming from languages like Java/C#, I found something missing in python.
I miss defining types for variables and methods.

Variables: Python vs Java

# Python Variables
name = "Tom"
cost = 5

// Java Variables
String name = "Tom"
int cost = 5

Methods: Python vs Java

# Python method

def add(a,b):
    return a + b

// Java method

public String add (String a, String b) {
    return a + b
}

What does the python version of the add function take? What does it return?

The add operator works for string, integers, list. Is that intended?

Some of the benefits of a language that supports types are:

• documentation of inputs and outputs
• capture error in wrong usage
• better code completion with IDE
  

  

Luckily for us, with PEP484 python 3.6 supports types.

Variables: Typed
With built in primitive types, all that is needed

# Python Variables
name: str = "Tom"
cost: int = 5

For more complex types,

from typing import List, Set, Dict, Tuple, Optional

elements: List[int] = [1,2]
unique_elems: Set[int] = {6, 7}

scores: Dict[str, float] = {'user1': 2.0, 'user_2':5.2}


info: Tuple[int, str] = (2, "tom")

Methods: Typed

from typing import Union, List

def add_nums(a:int,b:int) -> int:
    return a + b

def add (a:Union[List,str,int],b:Union[List,str,int] ) -> [List,str,int] :
    return a +b

Example of defining own types

from typing import Tuple

LatLngType = Tuple[float, float]

point: LatLngType = (50.12, 70.21) 

Type Checking

Python doesn’t have anything built in the language that enforces types.
However there is mypy, a project from Dropbox.

Installation

pip install mypy

Running

mypy test.py

Consider this sample code. Do you see the error(s)?

Looking at the output, we see that we are wrongly:

• forgot a return statement
• accessing an attribute that doesn’t exist

At my work, we have started including types and mypy as part of our work. It has made our code base more maintainable.