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of 56How do you create a basic Flask application?
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A basic Flask application requires creating a Flask instance and defining routes:
from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello_world():
return 'Hello, World!'
if __name__ == '__main__':
app.run(debug=True)
The Flask(__name__) creates the application instance, @app.route() decorator defines URL endpoints, and app.run() starts the development server.
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What is the significance of `__name__` in `Flask(__name__)`?
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The __name__ parameter helps Flask determine the root path of the application, which is used for:
- Resource location: Finding templates, static files, and other resources
- Import name: Used for extensions and debugging
- Module identification: Helps Flask understand the application's module structure
When run directly, __name__ equals '__main__', but when imported as a module, it contains the actual module name.
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How do you handle different HTTP methods in Flask routes?
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Specify HTTP methods using the methods parameter in the route decorator:
@app.route('/api/users', methods=['GET', 'POST'])
def handle_users():
if request.method == 'POST':
return create_user()
return get_users()
@app.route('/api/users/<int:user_id>', methods=['PUT', 'DELETE'])
def handle_user(user_id):
if request.method == 'PUT':
return update_user(user_id)
elif request.method == 'DELETE':
return delete_user(user_id)
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What are URL variables and how do you use them?
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URL variables capture dynamic parts of URLs and pass them as function arguments:
@app.route('/user/<username>')
def show_user(username):
return f'User: {username}'
@app.route('/post/<int:post_id>')
def show_post(post_id):
return f'Post ID: {post_id}'
@app.route('/path/<path:subpath>')
def show_subpath(subpath):
return f'Subpath: {subpath}'
Variable types include string (default), int, float, path, and uuid.
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What is URL building and how do you use `url_for()`?
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url_for() generates URLs for routes by endpoint name, providing URL reversal:
from flask import url_for
@app.route('/user/<username>')
def user_profile(username):
return f'Profile for {username}'
@app.route('/')
def index():
# Generate URL for user_profile endpoint
profile_url = url_for('user_profile', username='john')
return f'<a href="{profile_url}">John\'s Profile</a>'
Benefits include automatic URL updates when routes change and proper URL escaping.
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How do you handle query parameters in Flask?
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Access query parameters using request.args:
from flask import request
@app.route('/search')
def search():
query = request.args.get('q', '')
page = request.args.get('page', 1, type=int)
category = request.args.getlist('category') # Multiple values
return f'Query: {query}, Page: {page}, Categories: {category}'
Use get() for single values with defaults, getlist() for multiple values.
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How do you access request data in Flask?
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Flask provides the request object to access various types of request data:
from flask import request
@app.route('/form', methods=['POST'])
def handle_form():
# Form data
username = request.form['username']
email = request.form.get('email', '')
# JSON data
if request.is_json:
data = request.get_json()
# Files
if 'file' in request.files:
file = request.files['file']
# Headers
auth_header = request.headers.get('Authorization')
# Cookies
session_id = request.cookies.get('session_id')
return 'Data processed'
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What's the difference between `request.form`, `request.args`, and `request.get_json()`?
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These access different types of request data:
request.form: POST form data (application/x-www-form-urlencoded or multipart/form-data)request.args: URL query string parametersrequest.get_json(): JSON data from request body (application/json)
# URL: /api?page=1
# Body: {"name": "John"}
# Form data: username=admin
@app.route('/api', methods=['POST'])
def api():
page = request.args.get('page') # "1"
name = request.get_json()['name'] # "John"
username = request.form.get('username') # "admin"
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What are Flask's built-in response helpers?
How do you render templates in Flask?
How do you pass data to templates?
How do you handle forms in Flask?
How do you manage sessions in Flask?
How do you handle errors in Flask?
What are Flask environment variables and how do you use them?
What is WSGI and how does Flask relate to it?
Explain the Flask application context and request context.
How do you create URL rules dynamically?
How do you handle file uploads in Flask?
How do you create custom response objects?
What are the key features of Jinja2 templating?
What are Jinja2 filters and how do you create custom ones?
How do you handle template inheritance?
What is Flask-WTF and how does it help with forms?
How do you implement CSRF protection in Flask?
How do you perform custom form validation?
How do you integrate databases with Flask?
What are database migrations and how do you handle them?
How do you perform database queries in Flask-SQLAlchemy?
How do you define relationships between models?
What are the different session storage options in Flask?
How do you implement user authentication in Flask?
How do you implement custom exceptions?
How do you implement logging in Flask?
What are common security vulnerabilities in Flask applications?
How do you secure Flask applications?
How do you handle password security?
What are Flask Blueprints and why use them?
How do you structure a large Flask application?
What is the Application Factory pattern?
How do you create RESTful APIs with Flask?
How do you handle JSON serialization for complex objects?
How do you implement API versioning in Flask?
How do you test Flask applications?
How do you test API endpoints?
How do you mock dependencies in Flask tests?
How do you configure Flask applications for different environments?
How do you deploy Flask applications?
How do you implement rate limiting in Flask applications?
How do you handle database transactions in Flask?
How do you handle API authentication and authorization?
How do you implement caching in Flask?
How do you implement background tasks in Flask?
How do you implement WebSocket support in Flask?
How do you handle database connection pooling?
How do you implement custom middleware in Flask?
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Flask cheatsheet
Flask Cheat Sheet
- Summary01
- Flask Basics02
- Routing & Views03
- Request Handling04
- Templates (Jinja2)05
- Forms & Validation06
- Database Integration07
- Authentication & Sessions08
- RESTful APIs09
- Error Handling10
- Testing11
- Configuration & Deployment12
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