Common Mistakes Junior Developers Make with Flask and Their Potential Impacts
By hientd, at: July 10, 2024, 1:59 p.m.
Common Mistakes Junior Developers Make with Flask and Their Potential Impacts
Flask is a popular micro web framework for Python that is simple yet powerful, making it a great choice for beginners and experienced developers alike. However, juniors often make some common mistakes due to many reasons. In this post, we'll explore these mistakes and discuss their potential impacts on your project.
1. Ignoring the Application Factory Pattern
Mistake
Many beginners start with a single-file application, which can quickly become unmanageable as the project grows. They often ignore the application factory pattern, which is essential for creating scalable and testable Flask applications.
Example:
# Single-file application
from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello():
return "Hello, World!"
Potential Impact
Ignoring the application factory pattern can lead to a tightly coupled and monolithic codebase, making it difficult to manage, test, and scale the application as it grows.
Correct Approach
# Using application factory pattern
def create_app():
app = Flask(__name__)
@app.route('/')
def hello():
return "Hello, World!"
return app2. Hardcoding Configuration Values
Mistake
Hardcoding configuration values directly in the code can lead to security issues and make it difficult to manage different environments (development, testing, production).
Example:
app.config['SECRET_KEY'] = 'hardcoded_secret_key'
Potential Impact
Hardcoding configuration values can expose sensitive information in your source code and make it challenging to configure the application for different environments without modifying the code. We can use Bandit as checker here.
Correct Approach
# config.py
import os
class Config:
SECRET_KEY = os.environ.get('SECRET_KEY') or 'default_secret_key'
# app.py
from config import Config
app.config.from_object(Config)3. Not Using Blueprints
Mistake
Neglecting the use of blueprints can lead to a disorganized codebase, especially for larger applications.
Example:
# Single monolithic file with all routes
@app.route('/route1')
def route1():
pass
@app.route('/route2')
def route2():
pass Potential Impact
Without blueprints, the application can become cluttered and difficult to maintain as it grows, making it challenging to separate concerns and organize the code logically.
Correct Approach
# Using blueprints
from flask import Blueprint
bp = Blueprint('main', __name__)
@bp.route('/route1')
def route1():
pass
@bp.route('/route2')
def route2():
pass
# app.py
app.register_blueprint(bp)
4. Poor Error Handling
Mistake
Junior developers often overlook proper error handling, leading to unclear or insecure responses in case of failures.
Example:
@app.route('/data')
def data():
item = get_item()
return item.to_dict()
Potential Impact
Poor error handling can expose sensitive information, confuse users with unclear error messages, and make debugging and maintaining the application more difficult.
Correct Approach
@app.route('/data')
def data():
try:
item = get_item()
return item.to_dict()
except ItemNotFound:
return {"error": "Item not found"}, 404
except Exception as e:
return {"error": str(e)}, 505. Not Using Flask Extensions
Mistake
Many juniors try to reinvent the wheel instead of using Flask extensions, which can handle common tasks efficiently and securely.
Example:
# Writing custom authentication middleware
@app.before_request
def authenticate():
token = request.headers.get('Authorization')
if not token:
abort(401)
Potential Impact
Not using Flask extensions can lead to redundant and potentially insecure code, as well as missed opportunities to leverage community-vetted solutions for common tasks. Flask-owesome-libs is a great link to look at.
Correct Approach
# Using Flask-JWT-Extended for JWT authentication
from flask_jwt_extended import JWTManager
jwt = JWTManager(app)
# Configuration and initialization code
6. Ignoring Security Best Practices
Mistake
Ignoring security best practices, such as CSRF protection, input validation, and secure cookie handling, can lead to vulnerabilities.
Example:
@app.route('/submit', methods=['POST'])
def submit():
data = request.form['data']
process(data)Potential Impact
Ignoring security best practices can expose the application to attacks such as cross-site scripting (XSS), cross-site request forgery (CSRF), and SQL injection, compromising the integrity and security of the application.
Correct Approach
# Using Flask-WTF for form handling and CSRF protection
from flask_wtf import FlaskForm
from wtforms import StringField
from wtforms.validators import DataRequired
class MyForm(FlaskForm):
data = StringField('Data', validators=[DataRequired()])
@app.route('/submit', methods=['POST'])
def submit():
form = MyForm()
if form.validate_on_submit():
process(form.data.data)
return "Form submitted"
7. Improper Database Handling
Mistake
Not using SQLAlchemy or another ORM properly can lead to inefficient database interactions and potential SQL injection vulnerabilities.
Example:
# Executing raw SQL queries directly
@app.route('/user/<int:user_id>')
def user(user_id):
result = db.engine.execute(f'SELECT * FROM users WHERE id={user_id}')
user = result.fetchone()
return user</int:user_id><int:user_id></int:user_id>Potential Impact
Improper database handling can lead to inefficient queries, increased risk of SQL injection attacks, and difficulty in maintaining and scaling the database interactions within the application.
Correct Approach
# Using SQLAlchemy ORM - https://flask-sqlalchemy.palletsprojects.com/en/3.1.x/
@app.route('/user/<int:user_id>')
def user(user_id):
user = User.query.get(user_id)
return use</int:user_id><int:user_id></int:user_id>8. Not Handling Static Files and Templates Properly
Mistake
Improperly serving static files and templates can lead to broken pages and inefficient loading.
Example:
# Hardcoding paths to static files
@app.route('/home')
def home():
return '
'Potential Impact
Not handling static files and templates properly can result in broken images, styles, and scripts, leading to a poor user experience and increased maintenance efforts.
Correct Approach
# Using Flask's url_for to generate URLs for static files
@app.route('/home')
def home():
image_url = url_for('static', filename='image.png')
return f'
'Conclusion
By being aware of these common mistakes and understanding their potential impacts, junior/fresher developers can build more robust, maintainable, and secure Flask applications. Remember to follow best practices and leverage the rich ecosystem of Flask extensions to streamline development and enhance your application's quality.
