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Python Code Samples

Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.

7 matches
Errors & debugging easy

How to Mock a Failing Dependency to Test Error Paths in Python

Inject a fake HTTP client that raises a connection error to test how code handles dependency failures without touching the network.

testing mocking requests
Python 
import requests

def fetch_user(user_id):
    url = f"https://api.example.com/users/{user_id}"
    response = requests.get(url, timeout=5)
    response.raise_for_status()
    return response.json()

def get_user_name(user_id, http_client):
    try:
        user_data = http_client(user_id)
        return user_data["nam…
16 0 Open
Testing & modern typing easy

Dependency Injection in Python for Testability

Inject a config dependency into a service so you can swap a real environment-based config for a fake one in tests.

dependency-injection testing mocking
Python 
import os


class Config:
    """Simple config loader that can be easily faked in tests."""
    def get(self, key, default=None):
        return os.environ.get(key, default)


class UserService:
    def __init__(self, config):
        self.config = config

    def get_timeout(self):
        return int(self.config.get(…
16 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
System design patterns medium

How to Build an Adapter to Translate External API Responses in Python

Build an adapter class that translates a mock external API's response shape into your internal representation, keeping callers decoupled from the external contract.

adapter-pattern api architecture
Python 
import json
from typing import Dict, Any


class ExternalAPI:
    """Mock external service returning a different data shape."""
    def get_user(self, user_id: int) -> Dict[str, Any]:
        return {
            "id": user_id,
            "full_name": "Jane Doe",
            "email_address": "jane@example.com",
     …
14 0 Open
System design patterns medium

How to Migrate a Legacy Facade with the Strangler Fig Pattern in Python

Use a facade to wrap a legacy API and incrementally migrate callers to a modern interface, following the strangler fig pattern.

facade legacy migration
Python 
class LegacyAPI:
    """Simulates the legacy system's raw interface."""
    def get_user(self, user_id):
        return {"id": user_id, "name": "Alice", "legacy": True}


class UserService:
    """Facade that wraps the legacy system with a modern interface."""
    def __init__(self, legacy_api=None):
        self.lega…
12 0 Open
System design patterns easy

How to Mock Hexagonal Architecture Ports and Adapters in Python

Mock an email adapter in a hexagonal architecture with unittest.mock to test business logic in isolation.

hexagonal-architecture unittest-mock dependency-injection
Python 
from unittest.mock import Mock

class EmailService:
    def send(self, recipient, message):
        raise NotImplementedError

class OrderProcessor:
    def __init__(self, email_service):
        self.email_service = email_service
    
    def process_order(self, order_id, customer_email):
        # Business logic
   …
15 0 Open
System design patterns easy

How to mock the domain center in an onion architecture in Python

Define a repository interface and an in-memory mock to test domain services without touching infrastructure.

onion-architecture repository-pattern dependency-injection
Python 
from abc import ABC, abstractmethod
from dataclasses import dataclass
from typing import Dict, List, Optional


@dataclass
class Order:
    id: int
    customer: str
    items: List[str]
    total: float


class OrderRepository(ABC):
    @abstractmethod
    def find_by_id(self, order_id: int) -> Optional[Order]:
     …
11 0 Open

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  2. Open a sample, read How it works, and copy the code block
  3. Run it in the IDE, tweak values, then take a related quiz or tutorial lesson

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