Reference library

Testing & modern typing

pytest basics, mocks, type hints, TypedDict, Protocol, and static-checking patterns.

4 matches

How to Convert Strings to Types in Python Using TypeVar

A beginner-friendly helper that converts a string to int, float, bool, or str with type hints and graceful failure handling.

typing type-hints conversion

Python

from typing import TypeVar, Optional

T = TypeVar("T")

def convert_data(value: str, target_type: type[T]) -> Optional[T]:
    """Convert string value to target type; return None on failure."""
    try:
        if target_type is int:
            return int(value)
        elif target_type is float:
            return f…

14 0 Open

Testing & modern typing medium

How to Use Stubs, Fakes, Spies, and Mocks in Python Testing

Implement four types of test doubles — stubs, fakes, spies, and mocks — as subclasses of a PaymentGateway interface to replace real dependencies during testing.

testing mocks stubs

Python

class PaymentGateway:
    def charge(self, amount):
        raise NotImplementedError


class StubPaymentGateway(PaymentGateway):
    """Returns a fixed response without any logic."""
    def charge(self, amount):
        return {"success": True, "transaction_id": "stub-12345"}


class FakePaymentGateway(PaymentGatewa…

12 0 Open

Testing & modern typing easy

How to Use Union Type Hints in Python

This code demonstrates how to use Union type hints to specify that a parameter can accept multiple types (int, float, str) and handle them accordingly.

type-hints union typing

Python

from typing import Union

def process_value(value: Union[int, float, str]) -> str:
    if isinstance(value, (int, float)):
        return f"Number: {value * 2}"
    return f"String: {value.upper()}"

if __name__ == "__main__":
    print(process_value(10))
    print(process_value(3.14))
    print(process_value("hello"))

14 0 Open

Testing & modern typing medium

How to Validate Data in Python with Typing Hints

Build a runtime validation helper that checks values against Python type hints like Optional, list, and basic types.

typing validation type-hints

Python

from typing import Any, Optional, Union, TypeVar, get_origin, get_args

T = TypeVar("T")

def validate(value: Any, expected_type: type) -> Optional[str]:
    """Returns an error message if value doesn't match expected_type, else None."""
    # Handle Optional[...] types
    origin = get_origin(expected_type)
    if or…

14 0 Open

Browse by section

Each section groups closely related Python snippets.