Make a simple web app using Flask in Python
Flask is a small and lightweight Python web framework that provides useful tools and features that make creating web applications in Python easier.
Prerequisites
- Python3
- pip
- git (optional)
Venv
Starting python 3.3, module venv has been added to python standard library and can be used as a drop-in replacement for virtualenv.
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mkdir flask_app && cd flask_app
python -m venv env
active venv
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source env/bin/activate
you will see your environment is activated like this.
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(env)heston@localhost:$
I use git that easy to control my repo version. Remember to add the env dir in .gitignore
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git init
cat <<EOF >> .gitignore
env/
EOF
NOTE - Go to Link to check which thing should be ignore.
Install Flask
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pip install flask
check flask version
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python -c "import flask; print(flask.__version__)"
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Output installed packages in requirements format.
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pip freeze > requirements.txt
cat requirements.txt
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blinker==1.6.2
click==8.1.3
Flask==2.3.2
itsdangerous==2.1.2
Jinja2==3.1.2
MarkupSafe==2.1.2
Werkzeug==2.3.4
next time you can install the packages in easier way
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pip install -r requirements.txt
Create the app
vim app.py
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from flask import Flask
app = Flask(__name__)
@app.route('/')
@app.route('/index/')
def hello():
return '<h1>Hello, World!</h1>'
@app.route('/about/')
def about():
return '<h3>This is a Flask web application.</h3>'
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export FLASK_APP=app.py
export FLASK_ENV=development
Run the app.
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flask run --host=0.0.0.0 --port=5001
Go http://localhost:5001/about that will see
This is a Flask web application.
Dynamic Route
Use escape() function to render the word string as text. This is important to avoid XSS attacks, which can keep your web app safe.
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from markupsafe import escape
#...
@app.route('/capitalize/<word>/')
def capitalize(word):
return '<h1>{}</h1>'.format(escape(word.capitalize()))
To respond with an HTTP 404 error, you will need Flask’s abort() function, which can be used to make HTTP error responses. Change the second line in the file to also import this function:
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from markupsafe import escape
from flask import Flask, abort
#...
@app.route('/users/<int:user_id>/')
def greet_user(user_id):
users = ['Bob', 'Jane', 'Adam']
try:
return '<h2>Hi {}</h2>'.format(users[user_id])
except IndexError:
abort(404)
My final app.py file
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from markupsafe import escape
from flask import Flask, abort
app = Flask(__name__)
@app.route('/')
def hello():
return '<h1>Hello, World!</h1>'
@app.route('/about/')
def about():
return '<h3>This is a Flask web application.</h3>'
@app.route('/capitalize/<word>/')
def capitalize(word):
return '<h1>{}</h1>'.format(escape(word.capitalize()))
@app.route('/message/<msg>/')
def get(msg):
return {
'status': 'SUCCESS',
'message': msg
}
@app.route('/users/<int:user_id>/')
def greet_user(user_id):
users = ['Flask', 'Python', 'Django']
try:
return '<h2>Hi {}</h2>'.format(users[user_id])
except IndexError:
abort(404)