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name flask description Flask - Lightweight Python web framework for microservices, REST APIs, and flexible web applications with extensive extension ecosystem user-invocable false disable-model-invocation true version 1.0.0 category toolchain author Claude MPM Team license MIT progressive_disclosure {"entry_point":{"summary":"Lightweight Python web framework for microservices and REST APIs with flexible architecture and extensive extension ecosystem","when_to_use":"Building microservices, REST APIs with Flask-RESTful, lightweight web apps, when flexibility over batteries-included frameworks is needed, rapid prototyping","quick_start":"1. pip install flask 2. Create app.py with @app.route decorators 3. flask run 4. Access http://localhost:5000"}} context_limit 700 tags ["flask","python","web-framework","microservices","rest-api","lightweight","blueprints","sqlalchemy"] requires_tools []
Flask - Lightweight Python Web Framework
Overview
Flask is a micro-framework for Python web development, designed for building microservices, REST APIs, and flexible web applications. Its minimalist core and extensive extension ecosystem make it ideal for projects requiring lightweight architecture, rapid development, and full control over components.
Key Features :
Micro-framework philosophy (minimal core, extensible)
Flask-RESTful for API development
Blueprints for modular application structure
SQLAlchemy integration via Flask-SQLAlchemy
Jinja2 templating engine
Built-in development server with auto-reload
Werkzeug WSGI toolkit foundation
Large extension ecosystem (Flask-Login, Flask-JWT, Flask-CORS)
Production deployment with Gunicorn/uWSGI
Installation :
pip install flask
pip install flask flask-restful flask-sqlalchemy flask-login flask-cors
pip install flask flask-sqlalchemy psycopg2-binary
pip install flask flask-restful marshmallow flask-jwt-extended redis
Basic Application Patterns
1. Minimal Flask App
from flask import Flask, jsonify, request
app = Flask(__name__)
@app.route('/'
def hello ():
return jsonify({"message" : "Hello, World!" })
@app.route('/api/users/<int:user_id>'
def get_user (user_id ):
return jsonify({"id" : user_id, "name" : f"User {user_id} " })
@app.route('/api/users' , methods=['POST' ]
def
create_user
return
"id"
123
201
if
'__main__'
True
'0.0.0.0'
5000
python app.py
export FLASK_APP=app.py
export FLASK_ENV=development
flask run
flask run --port 8000 --host 0.0.0.0
2. Application Factory Pattern Recommended for production and testing:
from flask import Flask
from app.config import Config
from app.extensions import db, migrate, jwt
def create_app (config_class=Config ):
"""Application factory pattern."""
app = Flask(__name__)
app.config.from_object(config_class)
db.init_app(app)
migrate.init_app(app, db)
jwt.init_app(app)
from app.routes import api_bp, auth_bp
app.register_blueprint(api_bp, url_prefix='/api' )
app.register_blueprint(auth_bp, url_prefix='/auth' )
return app
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
from flask_jwt_extended import JWTManager
db = SQLAlchemy()
migrate = Migrate()
jwt = JWTManager()
import os
class Config :
SECRET_KEY = os.environ.get('SECRET_KEY' ) or 'dev-secret-key'
SQLALCHEMY_DATABASE_URI = os.environ.get('DATABASE_URL' ) or 'sqlite:///app.db'
SQLALCHEMY_TRACK_MODIFICATIONS = False
JWT_SECRET_KEY = os.environ.get('JWT_SECRET_KEY' ) or 'jwt-secret'
class DevelopmentConfig (Config ):
DEBUG = True
TESTING = False
class ProductionConfig (Config ):
DEBUG = False
TESTING = False
from app import create_app
app = create_app()
if __name__ == '__main__' :
app.run()
export FLASK_APP=run.py
flask run
3. Request and Response Handling from flask import Flask, request, jsonify, make_response, abort
app = Flask(__name__)
@app.route('/api/data' , methods=['GET' , 'POST' ]
def handle_data ():
if request.method == 'GET' :
page = request.args.get('page' , 1 , type =int )
limit = request.args.get('limit' , 10 , type =int )
return jsonify({
"page" : page,
"limit" : limit,
"data" : [...]
})
if request.method == 'POST' :
data = request.get_json()
if not data or 'name' not in data:
abort(400 , description="Missing required field: name" )
response = make_response(jsonify({"id" : 1 , **data}), 201 )
response.headers['X-Custom-Header' ] = 'value'
return response
@app.errorhandler(404
def not_found (error ):
return jsonify({"error" : "Resource not found" }), 404
@app.errorhandler(400
def bad_request (error ):
return jsonify({"error" : str (error.description)}), 400
Blueprints - Modular Applications
Blueprint Structure app/
├── __init__.py # Application factory
├── extensions.py # Extension instances
├── config.py # Configuration
├── models/
│ ├── __init__.py
│ ├── user.py
│ └── product.py
├── routes/
│ ├── __init__.py
│ ├── auth.py # Authentication routes
│ ├── users.py # User management routes
│ └── products.py # Product routes
└── services/
├── __init__.py
├── user_service.py
└── auth_service.py
Blueprint Implementation
from flask import Blueprint, jsonify, request
from app.models.user import User
from app.extensions import db
users_bp = Blueprint('users' , __name__)
@users_bp.route('/' , methods=['GET' ]
def list_users ():
"""List all users."""
page = request.args.get('page' , 1 , type =int )
per_page = request.args.get('per_page' , 20 , type =int )
users = User.query.paginate(page=page, per_page=per_page)
return jsonify({
"users" : [u.to_dict() for u in users.items],
"total" : users.total,
"page" : users.page,
"pages" : users.pages
})
@users_bp.route('/<int:user_id>' , methods=['GET' ]
def get_user (user_id ):
"""Get user by ID."""
user = User.query.get_or_404(user_id)
return jsonify(user.to_dict())
@users_bp.route('/' , methods=['POST' ]
def create_user ():
"""Create new user."""
data = request.get_json()
user = User(
email=data['email' ],
name=data['name' ]
)
user.set_password(data['password' ])
db.session.add(user)
db.session.commit()
return jsonify(user.to_dict()), 201
@users_bp.route('/<int:user_id>' , methods=['PUT' ]
def update_user (user_id ):
"""Update user."""
user = User.query.get_or_404(user_id)
data = request.get_json()
if 'name' in data:
user.name = data['name' ]
if 'email' in data:
user.email = data['email' ]
db.session.commit()
return jsonify(user.to_dict())
@users_bp.route('/<int:user_id>' , methods=['DELETE' ]
def delete_user (user_id ):
"""Delete user."""
user = User.query.get_or_404(user_id)
db.session.delete(user)
db.session.commit()
return '' , 204
def create_app ():
app = Flask(__name__)
from app.routes.users import users_bp
from app.routes.products import products_bp
app.register_blueprint(users_bp, url_prefix='/api/users' )
app.register_blueprint(products_bp, url_prefix='/api/products' )
return app
Flask-RESTful for APIs
Basic REST API
from flask import request
from flask_restful import Resource, Api, reqparse, fields, marshal_with
from app.models.user import User
from app.extensions import db
user_fields = {
'id' : fields.Integer,
'email' : fields.String,
'name' : fields.String,
'created_at' : fields.DateTime(dt_format='iso8601' )
}
class UserListResource (Resource ):
"""User collection endpoint."""
@marshal_with(user_fields )
def get (self ):
"""List all users."""
users = User.query.all ()
return users
def post (self ):
"""Create new user."""
parser = reqparse.RequestParser()
parser.add_argument('email' , required=True , help ='Email is required' )
parser.add_argument('name' , required=True , help ='Name is required' )
parser.add_argument('password' , required=True , help ='Password is required' )
args = parser.parse_args()
user = User(email=args['email' ], name=args['name' ])
user.set_password(args['password' ])
db.session.add(user)
db.session.commit()
return {'id' : user.id , 'email' : user.email, 'name' : user.name}, 201
class UserResource (Resource ):
"""Single user endpoint."""
@marshal_with(user_fields )
def get (self, user_id ):
"""Get user by ID."""
user = User.query.get_or_404(user_id)
return user
@marshal_with(user_fields )
def put (self, user_id ):
"""Update user."""
user = User.query.get_or_404(user_id)
parser = reqparse.RequestParser()
parser.add_argument('name' )
parser.add_argument('email' )
args = parser.parse_args()
if args['name' ]:
user.name = args['name' ]
if args['email' ]:
user.email = args['email' ]
db.session.commit()
return user
def delete (self, user_id ):
"""Delete user."""
user = User.query.get_or_404(user_id)
db.session.delete(user)
db.session.commit()
return '' , 204
from flask_restful import Api
def create_app ():
app = Flask(__name__)
api = Api(app, prefix='/api/v1' )
from app.api.resources import UserListResource, UserResource
api.add_resource(UserListResource, '/users' )
api.add_resource(UserResource, '/users/<int:user_id>' )
return app
Request Validation
Marshmallow Schemas
from marshmallow import Schema, fields, validate, validates, ValidationError
class UserSchema (Schema ):
"""User validation schema."""
id = fields.Int(dump_only=True )
email = fields.Email(required=True , validate=validate.Length(max =120 ))
name = fields.Str(required=True , validate=validate.Length(min =2 , max =80 ))
password = fields.Str(
required=True ,
load_only=True ,
validate=validate.Length(min =8 )
)
created_at = fields.DateTime(dump_only=True )
@validates('email'
def validate_email (self, value ):
"""Check email uniqueness."""
from app.models.user import User
if User.query.filter_by(email=value).first():
raise ValidationError('Email already registered' )
class UserUpdateSchema (Schema ):
"""User update schema (partial updates)."""
email = fields.Email(validate=validate.Length(max =120 ))
name = fields.Str(validate=validate.Length(min =2 , max =80 ))
password = fields.Str(load_only=True , validate=validate.Length(min =8 ))
from marshmallow import ValidationError
from app.schemas.user_schema import UserSchema, UserUpdateSchema
user_schema = UserSchema()
users_schema = UserSchema(many=True )
user_update_schema = UserUpdateSchema()
@users_bp.route('/' , methods=['POST' ]
def create_user ():
"""Create user with validation."""
try :
data = user_schema.load(request.get_json())
except ValidationError as err:
return jsonify({"errors" : err.messages}), 400
user = User(**data)
db.session.add(user)
db.session.commit()
return user_schema.dump(user), 201
@users_bp.route('/' , methods=['GET' ]
def list_users ():
"""List users with serialization."""
users = User.query.all ()
return jsonify(users_schema.dump(users))
Pydantic Validation
from pydantic import BaseModel, EmailStr, Field, validator
from typing import Optional
from datetime import datetime
class UserCreate (BaseModel ):
"""User creation schema."""
email: EmailStr
name: str = Field(..., min_length=2 , max_length=80 )
password: str = Field(..., min_length=8 )
@validator('password'
def password_complexity (cls, v ):
"""Validate password complexity."""
if not any (char.isdigit() for char in v):
raise ValueError('Password must contain at least one digit' )
if not any (char.isupper() for char in v):
raise ValueError('Password must contain at least one uppercase letter' )
return v
class UserUpdate (BaseModel ):
"""User update schema."""
email: Optional [EmailStr] = None
name: Optional [str ] = Field(None , min_length=2 , max_length=80 )
class UserResponse (BaseModel ):
"""User response schema."""
id : int
email: str
name: str
created_at: datetime
class Config :
orm_mode = True
from pydantic import ValidationError
@users_bp.route('/' , methods=['POST' ]
def create_user ():
"""Create user with Pydantic validation."""
try :
user_data = UserCreate(**request.get_json())
except ValidationError as e:
return jsonify({"errors" : e.errors()}), 400
user = User(
email=user_data.email,
name=user_data.name
)
user.set_password(user_data.password)
db.session.add(user)
db.session.commit()
return UserResponse.from_orm(user).dict (), 201
SQLAlchemy Integration
Models with Flask-SQLAlchemy
from datetime import datetime
from werkzeug.security import generate_password_hash, check_password_hash
from app.extensions import db
class User (db.Model):
"""User model."""
__tablename__ = 'users'
id = db.Column(db.Integer, primary_key=True )
email = db.Column(db.String(120 ), unique=True , nullable=False , index=True )
name = db.Column(db.String(80 ), nullable=False )
password_hash = db.Column(db.String(200 ), nullable=False )
is_active = db.Column(db.Boolean, default=True )
created_at = db.Column(db.DateTime, default=datetime.utcnow)
updated_at = db.Column(db.DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
posts = db.relationship('Post' , backref='author' , lazy='dynamic' , cascade='all, delete-orphan' )
def set_password (self, password ):
"""Hash and set password."""
self .password_hash = generate_password_hash(password)
def check_password (self, password ):
"""Verify password."""
return check_password_hash(self .password_hash, password)
def to_dict (self ):
"""Serialize to dictionary."""
return {
'id' : self .id ,
'email' : self .email,
'name' : self .name,
'is_active' : self .is_active,
'created_at' : self .created_at.isoformat(),
'updated_at' : self .updated_at.isoformat()
}
def __repr__ (self ):
return f'<User {self.email} >'
class Post (db.Model):
"""Post model."""
__tablename__ = 'posts'
id = db.Column(db.Integer, primary_key=True )
title = db.Column(db.String(200 ), nullable=False )
content = db.Column(db.Text, nullable=False )
user_id = db.Column(db.Integer, db.ForeignKey('users.id' ), nullable=False )
created_at = db.Column(db.DateTime, default=datetime.utcnow)
def to_dict (self ):
return {
'id' : self .id ,
'title' : self .title,
'content' : self .content,
'user_id' : self .user_id,
'author' : self .author.name,
'created_at' : self .created_at.isoformat()
}
@users_bp.route('/<int:user_id>/posts' , methods=['GET' ]
def get_user_posts (user_id ):
"""Get user posts with pagination."""
user = User.query.get_or_404(user_id)
page = request.args.get('page' , 1 , type =int )
posts = user.posts.paginate(page=page, per_page=20 )
return jsonify({
'posts' : [p.to_dict() for p in posts.items],
'total' : posts.total,
'page' : posts.page
})
Database Migrations
flask db init
flask db migrate -m "Create users table"
flask db upgrade
flask db downgrade
def upgrade ():
op.create_table(
'users' ,
sa.Column('id' , sa.Integer(), nullable=False ),
sa.Column('email' , sa.String(length=120 ), nullable=False ),
sa.Column('name' , sa.String(length=80 ), nullable=False ),
sa.Column('password_hash' , sa.String(length=200 ), nullable=False ),
sa.Column('created_at' , sa.DateTime(), nullable=True ),
sa.PrimaryKeyConstraint('id' ),
sa.UniqueConstraint('email' )
)
op.create_index('ix_users_email' , 'users' , ['email' ])
def downgrade ():
op.drop_index('ix_users_email' , table_name='users' )
op.drop_table('users' )
Authentication
Flask-Login Session-Based Auth
from flask_login import LoginManager
login_manager = LoginManager()
def create_app ():
app = Flask(__name__)
login_manager.init_app(app)
login_manager.login_view = 'auth.login'
@login_manager.user_loader
def load_user (user_id ):
from app.models.user import User
return User.query.get(int (user_id))
return app
from flask_login import UserMixin
class User (UserMixin, db.Model):
def get_id (self ):
return str (self .id )
from flask import Blueprint, request, jsonify
from flask_login import login_user, logout_user, login_required, current_user
from app.models.user import User
auth_bp = Blueprint('auth' , __name__)
@auth_bp.route('/login' , methods=['POST' ]
def login ():
"""User login."""
data = request.get_json()
user = User.query.filter_by(email=data['email' ]).first()
if not user or not user.check_password(data['password' ]):
return jsonify({"error" : "Invalid credentials" }), 401
login_user(user, remember=data.get('remember' , False ))
return jsonify(user.to_dict())
@auth_bp.route('/logout' , methods=['POST' ]
@login_required
def logout ():
"""User logout."""
logout_user()
return jsonify({"message" : "Logged out successfully" })
@auth_bp.route('/me' , methods=['GET' ]
@login_required
def get_current_user ():
"""Get current authenticated user."""
return jsonify(current_user.to_dict())
JWT Authentication
from flask_jwt_extended import JWTManager
jwt = JWTManager()
def create_app ():
app = Flask(__name__)
app.config['JWT_SECRET_KEY' ] = 'super-secret-key'
app.config['JWT_ACCESS_TOKEN_EXPIRES' ] = timedelta(hours=1 )
app.config['JWT_REFRESH_TOKEN_EXPIRES' ] = timedelta(days=30 )
jwt.init_app(app)
return app
from flask_jwt_extended import (
create_access_token,
create_refresh_token,
jwt_required,
get_jwt_identity
)
@auth_bp.route('/login' , methods=['POST' ]
def login ():
"""Login and return JWT tokens."""
data = request.get_json()
user = User.query.filter_by(email=data['email' ]).first()
if not user or not user.check_password(data['password' ]):
return jsonify({"error" : "Invalid credentials" }), 401
access_token = create_access_token(identity=user.id )
refresh_token = create_refresh_token(identity=user.id )
return jsonify({
"access_token" : access_token,
"refresh_token" : refresh_token,
"user" : user.to_dict()
})
@auth_bp.route('/refresh' , methods=['POST' ]
@jwt_required(refresh=True )
def refresh ():
"""Refresh access token."""
current_user_id = get_jwt_identity()
access_token = create_access_token(identity=current_user_id)
return jsonify({"access_token" : access_token})
@auth_bp.route('/me' , methods=['GET' ]
@jwt_required()
def get_current_user ():
"""Get current user from JWT."""
current_user_id = get_jwt_identity()
user = User.query.get_or_404(current_user_id)
return jsonify(user.to_dict())
@users_bp.route('/<int:user_id>' , methods=['DELETE' ]
@jwt_required()
def delete_user (user_id ):
"""Delete user (authenticated)."""
current_user_id = get_jwt_identity()
if current_user_id != user_id:
return jsonify({"error" : "Unauthorized" }), 403
user = User.query.get_or_404(user_id)
db.session.delete(user)
db.session.commit()
return '' , 204
Configuration Management
Environment-Based Configuration
import os
from datetime import timedelta
class Config :
"""Base configuration."""
SECRET_KEY = os.getenv('SECRET_KEY' , 'dev-secret-key-change-in-production' )
SQLALCHEMY_DATABASE_URI = os.getenv('DATABASE_URL' , 'sqlite:///app.db' )
SQLALCHEMY_TRACK_MODIFICATIONS = False
SQLALCHEMY_ECHO = False
JWT_SECRET_KEY = os.getenv('JWT_SECRET_KEY' , 'jwt-secret-change-in-production' )
JWT_ACCESS_TOKEN_EXPIRES = timedelta(hours=1 )
JWT_REFRESH_TOKEN_EXPIRES = timedelta(days=30 )
CORS_ORIGINS = os.getenv('CORS_ORIGINS' , '*' ).split(',' )
ITEMS_PER_PAGE = 20
MAX_ITEMS_PER_PAGE = 100
LOG_LEVEL = os.getenv('LOG_LEVEL' , 'INFO' )
LOG_FILE = os.getenv('LOG_FILE' , 'app.log' )
class DevelopmentConfig (Config ):
"""Development configuration."""
DEBUG = True
TESTING = False
SQLALCHEMY_ECHO = True
class TestingConfig (Config ):
"""Testing configuration."""
TESTING = True
SQLALCHEMY_DATABASE_URI = 'sqlite:///:memory:'
WTF_CSRF_ENABLED = False
class ProductionConfig (Config ):
"""Production configuration."""
DEBUG = False
TESTING = False
SECRET_KEY = os.getenv('SECRET_KEY' )
JWT_SECRET_KEY = os.getenv('JWT_SECRET_KEY' )
SQLALCHEMY_DATABASE_URI = os.getenv('DATABASE_URL' )
@classmethod
def init_app (cls, app ):
"""Production-specific initialization."""
import logging
from logging.handlers import SysLogHandler
syslog_handler = SysLogHandler()
syslog_handler.setLevel(logging.WARNING)
app.logger.addHandler(syslog_handler)
config_by_name = {
'development' : DevelopmentConfig,
'testing' : TestingConfig,
'production' : ProductionConfig,
'default' : DevelopmentConfig
}
def get_config (env_name='default' ):
"""Get configuration by environment name."""
return config_by_name.get(env_name, DevelopmentConfig)
def create_app (config_name='default' ):
app = Flask(__name__)
app.config.from_object(get_config(config_name))
return app
.env File Support
FLASK_APP=run.py
FLASK_ENV=development
SECRET_KEY=your-secret-key-here
JWT_SECRET_KEY=your-jwt-secret-here
DATABASE_URL=postgresql://user:password@localhost/dbname
CORS_ORIGINS=http://localhost:3000,http://localhost:8000
from dotenv import load_dotenv
load_dotenv()
import os
from dotenv import load_dotenv
def create_app ():
load_dotenv()
config_name = os.getenv('FLASK_ENV' , 'development' )
app = Flask(__name__)
app.config.from_object(get_config(config_name))
return app
Error Handling and Logging
Global Error Handlers
from flask import jsonify
from werkzeug.exceptions import HTTPException
from sqlalchemy.exc import SQLAlchemyError
def register_error_handlers (app ):
"""Register global error handlers."""
@app.errorhandler(404
def not_found_error (error ):
return jsonify({
"error" : "Not Found" ,
"message" : "The requested resource was not found"
}), 404
@app.errorhandler(400
def bad_request_error (error ):
return jsonify({
"error" : "Bad Request" ,
"message" : str (error.description) if hasattr (error, 'description' ) else "Invalid request"
}), 400
@app.errorhandler(401
def unauthorized_error (error ):
return jsonify({
"error" : "Unauthorized" ,
"message" : "Authentication required"
}), 401
@app.errorhandler(403
def forbidden_error (error ):
return jsonify({
"error" : "Forbidden" ,
"message" : "You don't have permission to access this resource"
}), 403
@app.errorhandler(500
def internal_error (error ):
app.logger.error(f'Internal server error: {error} ' )
db.session.rollback()
return jsonify({
"error" : "Internal Server Error" ,
"message" : "An unexpected error occurred"
}), 500
@app.errorhandler(HTTPException )
def handle_http_exception (error ):
"""Handle all HTTP exceptions."""
return jsonify({
"error" : error.name,
"message" : error.description
}), error.code
@app.errorhandler(SQLAlchemyError )
def handle_db_error (error ):
"""Handle database errors."""
app.logger.error(f'Database error: {error} ' )
db.session.rollback()
return jsonify({
"error" : "Database Error" ,
"message" : "A database error occurred"
}), 500
def create_app ():
app = Flask(__name__)
from app.errors.handlers import register_error_handlers
register_error_handlers(app)
return app
Logging Configuration
import logging
from logging.handlers import RotatingFileHandler
import os
def configure_logging (app ):
"""Configure application logging."""
if not app.debug and not app.testing:
if not os.path.exists('logs' ):
os.mkdir('logs' )
file_handler = RotatingFileHandler(
'logs/flask_app.log' ,
maxBytes=10240000 ,
backupCount=10
)
file_handler.setFormatter(logging.Formatter(
'%(asctime)s %(levelname)s: %(message)s '
'[in %(pathname)s:%(lineno)d]'
))
file_handler.setLevel(logging.INFO)
app.logger.addHandler(file_handler)
app.logger.setLevel(logging.INFO)
app.logger.info('Flask application startup' )
def create_app ():
app = Flask(__name__)
from app.logging_config import configure_logging
configure_logging(app)
return app
@users_bp.route('/' , methods=['POST' ]
def create_user ():
current_app.logger.info(f'Creating new user: {request.get_json()} ' )
current_app.logger.info(f'User created successfully: {user.id } ' )
Testing with pytest
Test Configuration
import pytest
from app import create_app
from app.extensions import db
from app.models.user import User
@pytest.fixture(scope='session' )
def app ():
"""Create application for testing."""
app = create_app('testing' )
with app.app_context():
db.create_all()
yield app
db.drop_all()
@pytest.fixture
def client (app ):
"""Flask test client."""
return app.test_client()
@pytest.fixture
def runner (app ):
"""Flask CLI test runner."""
return app.test_cli_runner()
@pytest.fixture
def db_session (app ):
"""Database session for testing."""
with app.app_context():
db.session.begin_nested()
yield db.session
db.session.rollback()
@pytest.fixture
def sample_user (db_session ):
"""Create sample user."""
user = User(email='test@example.com' , name='Test User' )
user.set_password('password123' )
db_session.add(user)
db_session.commit()
return user
@pytest.fixture
def auth_headers (client, sample_user ):
"""Get JWT authentication headers."""
response = client.post('/auth/login' , json={
'email' : 'test@example.com' ,
'password' : 'password123'
})
token = response.get_json()['access_token' ]
return {'Authorization' : f'Bearer {token} ' }
API Testing
import pytest
from app.models.user import User
def test_create_user (client ):
"""Test user creation endpoint."""
response = client.post('/api/users' , json={
'email' : 'new@example.com' ,
'name' : 'New User' ,
'password' : 'password123'
})
assert response.status_code == 201
data = response.get_json()
assert data['email' ] == 'new@example.com'
assert data['name' ] == 'New User'
assert 'id' in data
def test_get_user (client, sample_user ):
"""Test get user endpoint."""
response = client.get(f'/api/users/{sample_user.id } ' )
assert response.status_code == 200
data = response.get_json()
assert data['id' ] == sample_user.id
assert data['email' ] == sample_user.email
def test_list_users (client, sample_user ):
"""Test list users endpoint."""
response = client.get('/api/users' )
assert response.status_code == 200
data = response.get_json()
assert 'users' in data
assert len (data['users' ]) > 0
def test_update_user (client, sample_user, auth_headers ):
"""Test user update endpoint."""
response = client.put(
f'/api/users/{sample_user.id } ' ,
json={'name' : 'Updated Name' },
headers=auth_headers
)
assert response.status_code == 200
data = response.get_json()
assert data['name' ] == 'Updated Name'
def test_delete_user (client, sample_user, auth_headers ):
"""Test user deletion endpoint."""
response = client.delete(
f'/api/users/{sample_user.id } ' ,
headers=auth_headers
)
assert response.status_code == 204
assert User.query.get(sample_user.id ) is None
def test_authentication_required (client, sample_user ):
"""Test that protected endpoints require authentication."""
response = client.delete(f'/api/users/{sample_user.id } ' )
assert response.status_code == 401
Deployment
Production with Gunicorn
pip install gunicorn
gunicorn --workers 4 --bind 0.0.0.0:8000 "app:create_app()"
gunicorn --workers 4 --bind 0.0.0.0:8000 --env FLASK_ENV=production "app:create_app()"
import multiprocessing
bind = '0.0.0.0:8000'
backlog = 2048
workers = multiprocessing.cpu_count() * 2 + 1
worker_class = 'sync'
worker_connections = 1000
timeout = 30
keepalive = 2
accesslog = 'logs/access.log'
errorlog = 'logs/error.log'
loglevel = 'info'
proc_name = 'flask-app'
daemon = False
pidfile = 'gunicorn.pid'
Docker Deployment FROM python:3.11-slim
WORKDIR /app
# Install dependencies
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
# Copy application
COPY . .
# Create non-root user
RUN useradd -m -u 1000 flask && chown -R flask:flask /app
USER flask
# Run with Gunicorn
CMD ["gunicorn", "--config", "gunicorn.conf.py", "app:create_app()"]
version: '3.8'
services:
app:
build: .
ports:
- "8000:8000"
environment:
- FLASK_ENV=production
- DATABASE_URL=postgresql://user:password@db:5432/flask_db
- SECRET_KEY=${SECRET_KEY}
- JWT_SECRET_KEY=${JWT_SECRET_KEY}
depends_on:
- db
- redis
volumes:
- ./logs:/app/logs
db:
image: postgres:15-alpine
environment:
- POSTGRES_USER=user
- POSTGRES_PASSWORD=password
- POSTGRES_DB=flask_db
volumes:
- postgres_data:/var/lib/postgresql/data
redis:
image: redis:7-alpine
volumes:
- redis_data:/data
nginx:
image: nginx:alpine
ports:
- "80:80"
volumes:
- ./nginx.conf:/etc/nginx/nginx.conf:ro
depends_on:
- app
volumes:
postgres_data:
redis_data:
Microservices Patterns
Service Communication
import requests
from flask import current_app
class ExternalAPIService :
"""External API client service."""
def __init__ (self, base_url, timeout=10 ):
self .base_url = base_url
self .timeout = timeout
def get (self, endpoint, **kwargs ):
"""GET request to external API."""
url = f"{self.base_url} /{endpoint} "
try :
response = requests.get(url, timeout=self .timeout, **kwargs)
response.raise_for_status()
return response.json()
except requests.RequestException as e:
current_app.logger.error(f'External API error: {e} ' )
raise
def post (self, endpoint, data, **kwargs ):
"""POST request to external API."""
url = f"{self.base_url} /{endpoint} "
try :
response = requests.post(url, json=data, timeout=self .timeout, **kwargs)
response.raise_for_status()
return response.json()
except requests.RequestException as e:
current_app.logger.error(f'External API error: {e} ' )
raise
api_service = ExternalAPIService('https://api.example.com' )
@app.route('/proxy/data'
def proxy_data ():
"""Proxy request to external service."""
try :
data = api_service.get('data' )
return jsonify(data)
except Exception as e:
return jsonify({"error" : "External service unavailable" }), 503
Health Checks
from flask import Blueprint, jsonify
from app.extensions import db
from sqlalchemy import text
health_bp = Blueprint('health' , __name__)
@health_bp.route('/health'
def health_check ():
"""Basic health check."""
return jsonify({"status" : "healthy" }), 200
@health_bp.route('/health/ready'
def readiness_check ():
"""Readiness check with dependencies."""
checks = {
"database" : False ,
"status" : "unhealthy"
}
try :
db.session.execute(text('SELECT 1' ))
checks["database" ] = True
except Exception as e:
current_app.logger.error(f'Database health check failed: {e} ' )
checks["status" ] = "healthy" if all ([checks["database" ]]) else "unhealthy"
status_code = 200 if checks["status" ] == "healthy" else 503
return jsonify(checks), status_code
Best Practices
1. Use Application Factory Pattern
def create_app (config_name='default' ):
app = Flask(__name__)
app.config.from_object(get_config(config_name))
return app
app = Flask(__name__)
2. Use Blueprints for Modularity
from app.routes.users import users_bp
from app.routes.products import products_bp
app.register_blueprint(users_bp, url_prefix='/api/users' )
app.register_blueprint(products_bp, url_prefix='/api/products' )
3. Validate All Input
try :
data = user_schema.load(request.get_json())
except ValidationError as e:
return jsonify({"errors" : e.messages}), 400
data = request.get_json()
user = User(**data)
4. Use Environment Variables for Secrets
SECRET_KEY = os.getenv('SECRET_KEY' )
SECRET_KEY = 'hardcoded-secret-key'
5. Implement Proper Error Handling
@app.errorhandler(Exception )
def handle_error (error ):
app.logger.error(f'Error: {error} ' )
return jsonify({"error" : "Internal server error" }), 500
Resources
Related Skills When using Flask, consider these complementary skills:
pytest : Testing Flask applications with fixtures and test clientsqlalchemy : Database ORM patterns with Flask-SQLAlchemy integrationfastapi-local-dev : Modern async alternative for high-performance APIsdjango : Batteries-included framework with built-in admin and ORM
Quick Flask Testing Patterns (Inlined for Standalone Use)
import pytest
from flask import Flask
from app import create_app, db
@pytest.fixture
def app ():
"""Create and configure test app"""
app = create_app('testing' )
with app.app_context():
db.create_all()
yield app
db.drop_all()
@pytest.fixture
def client (app ):
"""Test client for making requests"""
return app.test_client()
@pytest.fixture
def runner (app ):
"""CLI test runner"""
return app.test_cli_runner()
def test_home_page (client ):
response = client.get('/' )
assert response.status_code == 200
assert b'Welcome' in response.data
def test_api_endpoint (client ):
response = client.post('/api/users' , json={
'username' : 'alice' ,
'email' : 'alice@example.com'
})
assert response.status_code == 201
data = response.get_json()
assert data['username' ] == 'alice'
def test_authentication (client ):
response = client.post('/login' , data={
'username' : 'alice' ,
'password' : 'secret123'
})
assert response.status_code == 302
response = client.get('/dashboard' )
assert response.status_code == 200
def test_user_creation (app ):
with app.app_context():
user = User(username='bob' , email='bob@example.com' )
db.session.add(user)
db.session.commit()
found = User.query.filter_by(username='bob' ).first()
assert found is not None
assert found.email == 'bob@example.com'
def test_404_error (client ):
response = client.get('/nonexistent' )
assert response.status_code == 404
assert b'Not Found' in response.data
Quick SQLAlchemy Integration (Inlined for Standalone Use)
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy.orm import DeclarativeBase
class Base (DeclarativeBase ):
pass
db = SQLAlchemy(model_class=Base)
def create_app ():
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI' ] = 'postgresql://user:pass@localhost/db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS' ] = False
db.init_app(app)
with app.app_context():
db.create_all()
return app
class User (db.Model):
__tablename__ = 'users'
id = db.Column(db.Integer, primary_key=True )
username = db.Column(db.String(50 ), unique=True , nullable=False )
email = db.Column(db.String(100 ), unique=True , nullable=False )
posts = db.relationship('Post' , backref='author' , lazy='dynamic' )
class Post (db.Model):
__tablename__ = 'posts'
id = db.Column(db.Integer, primary_key=True )
title = db.Column(db.String(200 ), nullable=False )
content = db.Column(db.Text, nullable=False )
user_id = db.Column(db.Integer, db.ForeignKey('users.id' ), nullable=False )
@app.route('/users/<int:user_id>'
def get_user (user_id ):
user = db.session.get(User, user_id)
if not user:
abort(404 )
return jsonify({
'id' : user.id ,
'username' : user.username,
'email' : user.email,
'posts' : [{'title' : p.title} for p in user.posts]
})
@app.route('/users' , methods=['POST' ]
def create_user ():
data = request.get_json()
user = User(username=data['username' ], email=data['email' ])
db.session.add(user)
db.session.commit()
return jsonify({'id' : user.id }), 201
from sqlalchemy.exc import IntegrityError
@app.route('/transfer' , methods=['POST' ]
def transfer_funds ():
try :
sender = User.query.get_or_404(request.json['sender_id' ])
receiver = User.query.get_or_404(request.json['receiver_id' ])
amount = request.json['amount' ]
sender.balance -= amount
receiver.balance += amount
db.session.commit()
return jsonify({'status' : 'success' })
except IntegrityError:
db.session.rollback()
return jsonify({'error' : 'Transaction failed' }), 400
Quick FastAPI Comparison (Inlined for Standalone Use) When to Choose FastAPI over Flask:
Need async/await for high concurrency
Want automatic API documentation (OpenAPI/Swagger)
Require built-in data validation (Pydantic)
Building modern microservices or GraphQL APIs
Need WebSocket or Server-Sent Events support
When to Stick with Flask:
Building traditional server-rendered web apps
Existing large Flask codebase
Need mature ecosystem and extensive plugins
Team familiar with synchronous Python patterns
Simpler deployment (no async runtime complexity)
Migration Considerations:
@app.route('/users/<int:user_id>'
def get_user (user_id ):
user = User.query.get_or_404(user_id)
return jsonify({'id' : user.id , 'name' : user.name})
@app.get('/users/{user_id}' , response_model=UserResponse
async def get_user (user_id: int , db: AsyncSession = Depends(get_db ) ):
user = await db.get(User, user_id)
if not user:
raise HTTPException(status_code=404 , detail="User not found" )
return user
[Full pytest, SQLAlchemy, and FastAPI patterns available in respective skills if deployed together]
