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Testing & modern typing

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

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How to Group Data by Key in Python with Type Hints

Group a list of dictionaries by a specified key using a typed helper function and print a summary of each group.

from typing import Any, Dict, List, TypeVar, Union

T = TypeVar("T")

def group_by(data: List[Dict[str, Any]], key: str) -> Dict[Any, List[Dict[str, Any]]]:
    """Group a list of dictionaries by a given key."""
    grouped: Dict[Any, List[Dict[str, Any]]] = {}
    for item in data:
        value = item.get(key)
     …

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Testing & modern typing easy

How to Test Hypotheses with Property-Based Check in Python

A Python search that checks an integer property (palindrome divisible by digit sum) and returns the first counterexample within a range, with exactly reproduced output from the code.

hypothesis testing palindrome

Python

def is_property_satisfied(n):
    """
    Demonstrates a mathematically inspired property:
    checks whether n is both a palindrome and divisible by its digit sum.
    """
    s = str(n)
    if s != s[::-1]:
        return False
    digit_sum = sum(int(d) for d in s)
    return digit_sum != 0 and n % digit_sum == 0

…

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Testing & modern typing easy

How to Write a Contract Test with Mock in Python

Use unittest.mock to verify a consumer's expectations match the provider's response shape in a Python contract test.

contract-testing unittest mock

Python

from unittest.mock import Mock

# Contract test: verify consumer expects data shape that provider delivers.
# We mock the provider and assert the consumer's calls match the agreed contract.

def fetch_user(provider_client, user_id):
    """Consumer code: expects provider to return {'id', 'name', 'email'}."""
    respo…

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