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Testing & modern typing

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

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Dataclass with Type Hints Fields in Python

Create a data class with typed fields and default values, then instantiate and inspect it.

from dataclasses import dataclass


@dataclass
class Person:
    name: str
    age: int
    email: str = "unknown@example.com"
    is_active: bool = True


if __name__ == "__main__":
    person = Person(name="Alice", age=30)
    print(person)
    print(f"Name: {person.name}, Age: {person.age}, Email: {person.email}, A…

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Testing & modern typing easy

Design Data Helpers with Python TypedDict and Literal

Use TypedDict, Literal, and Union to define typed data shapes and parse values in Python.

typeddict literal union

Python

from typing import TypedDict, Literal, Optional, Union, List

class User(TypedDict):
    name: str
    age: int
    role: Literal["admin", "user", "guest"]

def describeUser(data: User) -> str:
    return f"{data['name']} ({data['age']}) — {data['role']}"

def parse_value(item: Union[int, str, None]) -> str:
    if it…

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Testing & modern typing easy

How to Use Basic Type Hints (int, str) for Return Values in Python

Declare a simple function with int and str type hints and a typed return value in Python.

type-hints annotations functions

Python

def greet(name: str, age: int) -> str:
    return f"{name} is {age} years old."


if __name__ == "__main__":
    print(greet("Alice", 30))

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Testing & modern typing easy

How to Use Literal Type Hints in Python

Use typing.Literal to restrict a function parameter to specific allowed string values and get static type checking.

typing type-hints literal

Python

from typing import Literal

def get_status_message(status: Literal["active", "inactive", "pending"]) -> str:
    """Return a message based on the status value."""
    if status == "active":
        return "Account is active"
    elif status == "inactive":
        return "Account is inactive"
    else:
        return "…

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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…

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Testing & modern typing easy

How to use unittest mock side_effect with a sequence in Python

Demonstrates using Mock.side_effect with a list to return different values per call and raise an exception at a specific call in unittest.

unittest mock side_effect

Python

import unittest
from unittest.mock import Mock

class TestMockSideEffectSequence(unittest.TestCase):
    def test_side_effect_sequence(self):
        mock = Mock()
        mock.side_effect = [1, 2, 3, Exception("boom")]
        
        self.assertEqual(mock(), 1)
        self.assertEqual(mock(), 2)
        self.asser…

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