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How to use Python as static type language

· 2 min read
Sandip Sadhukhan

Why use static typing?: Static type languages can catch type-related errors at compile-time, resulting in safer and more efficient code, but may require more upfront work.

Python as Static type language

How to use?​

We can use mypy to type check. Add this in your vscode settings file to get started with typechecking.

First install mypy​

pip3 install mypy

How to enable typechecking in vscode​

Add this settings in your vscode to enable typechecking

{
    "python.analysis.typeCheckingMode": "strict",
    "python.linting.mypyEnabled": true,
}

Then error will shown directly on vscode

Vscode Mypy

Normal types​

from typing import Union, Optional, List, TypeVar

a: int = 3
b: str = "33"
c: Union[int, str] = "32"
d: Optional[int] = None
e: List[str] = ["hello", "33"]

# general type
strOrInt =  TypeVar("strOrInt", str, int)

def get_sum(a: strOrInt, b: strOrInt) -> strOrInt:
    return a + b

Interface like syntax​

from typing_extensions import Protocol

class Renderable(Protocol):
    def render(self) -> str: ...

def render(obj: Renderable) -> str:
    return obj.render()

class Foo:
    def render(self) -> str:
        return "Foo!"

render(Foo())

How to avoid typing for some particular case like legacy code etc​

#1: use Any
def func(a:str) -> Any:
        return something(a)

#2: cast
p: Any =  33

def fun(p:int) -> int:
    return p + 1
# any will not throw error, but this is just an example
fun(cast(int, p))

#3 ignore
func("hdll") # type: ignore