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Flask

Python web framework for building web applications and APIs

10 min read
flaskpythonbackendapiwebwsgi
Official Docs

Setup & Basics

Initialize and configure Flask applications

Application Setup

Create and configure Flask app

python
💡 Use environment variables for configuration
🔍 Flask(__name__) creates the application instance
⚡ debug=True enables auto-reload and detailed errors
setupconfiguration

Routing

Define routes and handle HTTP methods

Route Handling

Define and organize routes

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💡 Use variable rules like <int:id> for type conversion
🔍 get_or_404() automatically returns 404 if not found
⚡ Specify methods parameter to handle multiple HTTP verbs
routingendpoints

Request & Response

Handle request data and send responses

Request/Response Handling

Work with request and response objects

python
💡 jsonify() automatically sets Content-Type to application/json
🔍 request.get_json() parses JSON request body
⚡ make_response() gives full control over response
requestresponse

Blueprints

Organize application with blueprints

Blueprint Organization

Structure large applications with blueprints

python
💡 Blueprints help organize code into modules
🔍 url_prefix applies to all blueprint routes
⚡ Each blueprint can have its own error handlers
blueprintsorganization

Database Integration

Connect and work with databases using SQLAlchemy

SQLAlchemy Setup

Integrate Flask with SQLAlchemy ORM

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💡 Use Flask-Migrate for database migrations
🔍 SQLAlchemy provides powerful ORM capabilities
⚡ Use lazy loading for relationships to optimize queries
📌 Always use app context when working with db outside request
databasesqlalchemy

Authentication

Implement user authentication and sessions

Authentication Implementation

User login and session management

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🔒 Always hash passwords with werkzeug.security
💡 Use Flask-Login for session management
🔍 JWT tokens for API authentication
⚡ @login_required decorator protects routes
authenticationsecurity

Error Handling

Handle errors gracefully

Error Handlers

Catch and handle application errors

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💡 Custom exceptions provide better error context
🔍 Log errors for debugging in production
⚡ Don't expose internal errors to users
📌 HTTPException covers all HTTP status codes
errorsexceptions

Middleware & Hooks

Process requests with middleware and hooks

Request Hooks

Execute code before and after requests

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💡 Use g object to store request-scoped data
🔍 before_request can return early to abort request
⚡ after_request modifies all responses
📌 teardown runs even if exception occurs
middlewarehooks

Testing

Test Flask applications

Testing Flask Apps

Write tests for Flask applications

python
💡 Use pytest fixtures for test setup
🔍 Test with in-memory database for speed
⚡ test_client() provides request simulation
📌 Test both success and failure cases
testingpytest

Deployment

Deploy Flask applications to production

Production Deployment

Deploy Flask apps with WSGI servers

python
💡 Use Gunicorn or uWSGI for production
🔍 Place Nginx in front for static files and SSL
⚡ Enable connection pooling for databases
📌 Set FLASK_ENV=production for security
deploymentproduction

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