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Testing & modern typing

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

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Fix and Test a Regression Bug in Python with Unit Tests

This code implements a circle area function that raises ValueError for negative radii, then runs basic tests and a regression check for that edge case.

regression-testing unit-testing math

Python

import math

def calculate_area(radius):
    """Calculate the area of a circle given its radius."""
    if radius < 0:
        raise ValueError("Radius cannot be negative")
    return math.pi * radius ** 2

def main():
    test_cases = [0, 1, 2.5, 5, 10]
    
    print("Circle Area Calculator")
    print("-" * 30)
   …

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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 Python Type Hints for Beginners

Build a data helper module with basic type hints — Union, Optional, List, Dict, Any, and TypeVar — to make your code clearer and safer.

type-hints typing annotations

Python

from typing import Any, Union, Optional, List, Dict, Tuple, Callable, TypeVar

T = TypeVar("T")

def describe(value: Any) -> str:
    """Return a human-readable description of the value's type."""
    if isinstance(value, list):
        return f"list of {len(value)} items"
    elif isinstance(value, dict):
        ret…

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Testing & modern typing easy

How to Validate Dataclass Fields with Python Type Hints

A beginner-friendly helper that checks if instance attributes match their declared type hints using dataclasses and get_type_hints.

dataclasses type-hints validation

Python

from typing import Any, TypeVar, get_type_hints
from dataclasses import dataclass

T = TypeVar("T")

@dataclass
class User:
    name: str
    age: int
    email: str

def validate_fields(obj: Any) -> dict[str, bool]:
    """Check if object attributes match declared type hints."""
    hints = get_type_hints(obj.__class…

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