Flask Cheat Sheet

May 26, 2021

12:30 pm

keyword arguments

Keyword arguments (or named arguments) are values that, when passed into a function, are identifiable by specific parameter names.
A keyword argument is preceded by a parameter and the assignment operator, = . Keyword arguments can be likened to dictionaries in that they map a value to a keyword.

The order of the arguments does not matter

def my_function(child3, child2, child1):
  print("The youngest child is " + child3)

my_function(child1 = "Emil", child2 = "Tobias", child3 = "Linus")

The phrase Keyword Arguments are often shortened to kwargs in Python documentations.

arguments vs keyword arguments (*args vs **kwargs)

def foo(*args, **kwargs):
    print(args);
    print(kwargs);
    
foo(5, 6, 7, name="Shailesh", age=32, city="Nagpur");

output

Decorators

A decorator is a design pattern in Python that allows a user to add new functionality to an existing object without modifying its structure.
Decorators are usually called before the definition of a function you want to decorate.

### CREATE CUSTOM DECORATOR ###
from functools import wraps

def my_decorator(f):
    @wraps(f)
    def msg(*args, **kwargs):
        print("I am from custom decorator")
        print("Arguments:", args)
        print("Keyword Arguments:", kwargs)
        
        return f(*args, **kwargs)
        
    return msg;


@my_decorator    
def add(x, y):
    print(f"{x} + {y} = {x + y}")

    
@my_decorator
def sub(x, y):
    print(f"{x} - {y} = {abs(x - y)}")
    
    
#invoke functions
add(5, y=6)
sub(5, y=6)

Flask Framework

Flask is a micro web framework written in Python. It is classified as a microframework because it does not require particular tools or libraries.
It has no database abstraction layer, form validation, or any other components where pre-existing third-party libraries provide common functions.

install flask module

python -m pip install Flask

hello world

from flask import Flask, jsonify, request, render_template

app = Flask(__name__)

#YOUR FUNCTIONS HERE

if __name__ == "__main__":
    app.run(debug=True);
    #app.run(host="0.0.0.0", port=int("1234"), debug=True)

render html template [NOTE: MAKE SURE TO KEEP ALL TEMPLATE FILES IN templates DIRECTORY]

@app.route('/')
def index():
    #return "Hello World";
    
    data = {'company_name': "TCET"}
    return render_template('hello_world.html', data = data)

templates/hello_world.html

<h1>Hello World</h1>
<h3>Welcome to {{data['company_name']}}</h3>

read get value

@app.route('/sqr', methods=['GET'])
def getSqr():
    num1 = int(request.args.get('num1'));
    return f"Square of {num1} is {num1 * num1}"


@app.route('/add', methods=['GET'])
def add():
    num1 = int(request.args.get('num1'));
    num2 = int(request.args.get('num2'));
    
    return f"{num1} + {num2} = {num1 + num2}";

read post value

@app.route('/sub', methods=['POST'])
def sub():
    num1 = int(request.form.get('num1'));
    num2 = int(request.form.get('num2'));
    
    return f"{num1} - {num2} = {num1 - num2}";

read raw json

@app.route('/mul', methods=['POST'])
def mul():
    raw_json = request.get_json();
    num1 = int(raw_json['num1']);
    num2 = int(raw_json['num2']);
    
    return f"{num1} * {num2} = {num1 * num2}";

install pymysql module

python -m pip install PyMySQL

install cors module

python -m pip install -U flask-cors

get users from database

from flask import Flask, jsonify, request
from flask_cors import CORS
import pymysql

app = Flask(__name__)
cors = CORS(app)

@app.route('/users', methods=['GET'])
def get_users():
    # To connect MySQL database
    conn = pymysql.connect(host='localhost', user='root', password = "", db='databasename')
        
    cur = conn.cursor()
    cur.execute("select * from users LIMIT 10")
    output = cur.fetchall()

    print(type(output)); #this will print tuple	

    for rec in output:
        print(rec);
        
    # To close the connection
    conn.close()

    return jsonify(output);

fetch data using javascript fetch api

let url = "http://localhost:5000";
fetch(url)
    .then(response => response.json())
    .then(response => console.table(response));

Flask RESTful API

Flask-RESTful is an extension for Flask that adds support for quickly building REST APIs.

install flask-restful

python -m pip install flask-restful

MyApi Resource

from flask import Flask, request
from flask_restful import Resource, Api

app = Flask(__name__)
api = Api(app)

class MyApi(Resource):
    def __init__(self):
        print("Constructor called...")
        
    def get(self):
        return {"msg" : "get method"}
        
    def post(self):
        return {"msg" : "post method"}
        
    def put(self):
        return {"msg" : "put method"}
    
    def delete(self):
        return {"msg" : "delete method"}
    
    
api.add_resource(MyApi, '/myapiurl')

if __name__ == "__main__":
    app.run(debug=True)

Authenticate REST API

from flask import Flask, request, make_response
from flask_restful import Resource, Api
from functools import wraps


app = Flask(__name__)
api = Api(app)


#define custom decorator @authorize
def authorize(f):
    @wraps(f)
    def kuchbhi(*args, **kwargs):
        err_msg = "Authentication required";
    
        if(request.authorization == None):
            return make_response('Not Authorized', 403, {'WWW-Authenticate' : err_msg})
            
        unm = request.authorization.username
        pwd = request.authorization.password
        
        if(unm == 'admin' and pwd == 'admin@123'):
            print("Correct username and password")
            return f(*args, **kwargs)
        
        return make_response('Not Authorized', 403, {'WWW-Authenticate' : err_msg})
    
    return kuchbhi


class MyApi(Resource):
    
    def __init__(self):
        print("Constructor called...")

    @authorize 
    def get(self):
        return {"msg" : "get method"}

    @authorize    
    def post(self):
        return {"msg" : "post method"}

    @authorize    
    def put(self):
        return {"msg" : "put method"}

    @authorize
    def delete(self):
        return {"msg" : "delete method"}
    
api.add_resource(MyApi, '/myapiurl')

if __name__ == "__main__":
    app.run(debug=True)

apply authorize decorator to all methods of call

from flask import Flask, request, make_response
from flask_restful import Resource, Api
from functools import wraps

app = Flask(__name__)
api = Api(app)

#define custom decorator authorize
def authorize(f):
    @wraps(f)
    def kuchbhi(*args, **kwargs):
        err_msg = "Authentication required";
    
        if(request.authorization == None):
            return make_response('Not Authorized', 403, {'WWW-Authenticate' : err_msg})
            
        unm = request.authorization.username
        pwd = request.authorization.password
        
        if(unm == 'admin' and pwd == 'admin@123'):
            print("Correct username and password")
            return f(*args, **kwargs)
        
        return make_response('Not Authorized', 403, {'WWW-Authenticate' : err_msg})
    
    return kuchbhi


class MyApi(Resource):
    method_decorators = [authorize]
    
    def __init__(self):
        print("Constructor called...")
        
    def get(self):
        return {"msg" : "get method"}
        
    def post(self):
        return {"msg" : "post method"}
        
    def put(self):
        return {"msg" : "put method"}
    
    def delete(self):
        return {"msg" : "delete method"}
    
api.add_resource(MyApi, '/myapiurl')

if __name__ == "__main__":
    app.run(debug=True)

Testing API

test response status
test_myapiapp.py
where myapiapp.py is the file where all restful api defined

#from filename import app
from rest_api import app
import unittest
import base64

class RestAPITest(unittest.TestCase):
    
    def test_status(self):
        tester = app.test_client(self)
        response = tester.get('/myapiurl')
        self.assertEqual(response.status_code, 200)
   
if __name__ == "__main__":
    unittest.main()

test content type

def test_content_type(self):
    tester = app.test_client(self)
    response = tester.get('/myapiurl')

    self.assertEqual(response.content_type, "application/json")

test content data

def test_content(self):
    tester = app.test_client(self)
    response = tester.get('/myapiurl')        
    self.assertTrue(b'get' in response.data)

To pass Basic Auth credentials in header

creds = base64.b64encode(b"admin:admin@123").decode("utf-8")
response = tester.get('/myapiurl', headers={"Authorization": f"Basic {creds}"})

complete test file code

#from filename import app
from rest_api import app
import unittest
import base64

class RestAPITest(unittest.TestCase):
    
    def test_status(self):
        tester = app.test_client(self)
        #response = tester.get('/myapiurl')
        
        creds = base64.b64encode(b"admin:admin@123").decode("utf-8")
        response = tester.get('/myapiurl', headers={"Authorization": f"Basic {creds}"})
        
        self.assertEqual(response.status_code, 200)
        
    
    def test_content_type(self):
        tester = app.test_client(self)
        #response = tester.get('/myapiurl')
        
        creds = base64.b64encode(b"admin:admin@123").decode("utf-8")
        response = tester.get('/myapiurl', headers={"Authorization": f"Basic {creds}"})
        
        self.assertEqual(response.content_type, "application/json")
        
        
    def test_content(self):
        tester = app.test_client(self)
        #response = tester.get('/myapiurl')
        
        creds = base64.b64encode(b"admin:admin@123").decode("utf-8")
        response = tester.get('/myapiurl', headers={"Authorization": f"Basic {creds}"})
        
        self.assertTrue(b'get' in response.data)
        
        
if __name__ == "__main__":
    unittest.main()

REST API CRUD

app.py

import pymysql

from flask import Flask, jsonify, request
from flask_cors import CORS
import pymysql

app = Flask(__name__)
cors = CORS(app)

# To connect MySQL database
conn = pymysql.connect(host='yourhost', user='youruser', password = "yourpassword", db='yourdatabase')

@app.route('/users', methods=['GET'])
def get_users():

    cur = conn.cursor(pymysql.cursors.DictCursor)
    cur.execute("select * from users LIMIT 10")
    output = cur.fetchall()

    print(type(output)); #this will print tuple

    for rec in output:
        print(rec);

    # To close the connection
    #conn.close()

    return jsonify(output);


@app.route('/users/get_one_record', methods=['GET'])
def get_single_user():

    cur = conn.cursor(pymysql.cursors.DictCursor)
    userid = int(request.args.get('id'));
    cur.execute(f"select * from users WHERE id = {userid}")
    output = cur.fetchone()
    
    return jsonify(output);



@app.route('/users', methods=['DELETE'])
def deleteRecord():
    cur = conn.cursor()
    id = int(request.args.get('id'));

    query = f"delete from users where id = {id}";
    #print(query)
    res = cur.execute(query);
    conn.commit();
    print(cur.rowcount, "record(s) deleted")

    return "Record deleted sussesfully"

@app.route('/users', methods=['POST'])
def insertRecord():

        #get raw json values
        raw_json = request.get_json();
        name= raw_json['name'];
        age= raw_json['age'];
        city= raw_json['city'];

        sql="INSERT INTO users (id,name,age,city) VALUES (NULL,'"+name+"','"+str(age)+"','"+city+"')";
        cur= conn.cursor()

        cur.execute(sql);
        conn.commit()
        return "Record inserted Succesfully"

@app.route('/users', methods=['PUT'])
def updateRecord():

        raw_json = request.get_json();

        #print(type(raw_json));

        id = raw_json['id'];
        name= raw_json['name'];
        age= raw_json['age'];
        city= raw_json['city'];
        sql_update_quary=("UPDATE users SET name = '"+name+"',age = '"+str(age)+"',city = '"+city+"'WHERE id = '"+str(id)+"'");
        cur= conn.cursor()
        cur.execute(sql_update_quary);
        conn.commit()
        return "Record Updated Sussecfully";


if __name__ == "__main__":
    #app.run(debug=True);
    app.run(host="0.0.0.0", port=int("1235"), debug=True)

script.js

//const api_url = "<heroku_app_url>"
const api_url = "http://localhost:8080/users"

function loadData(records = []) {
	var table_data = "";
	for(let i=0; i<records.length; i++) {
		table_data += `<tr>`;
		table_data += `<td>${records[i].name}</td>`;
		table_data += `<td>${records[i].age}</td>`;
		table_data += `<td>${records[i].city}</td>`;
		table_data += `<td>`;
		table_data += `<a href="edit.html?id=${records[i].id}"><button class="btn btn-primary">Edit</button></a>`;
		table_data += '&nbsp;&nbsp;';
		table_data += `<button class="btn btn-danger" onclick=deleteData('${records[i].id}')>Delete</button>`;
		table_data += `</td>`;
		table_data += `</tr>`;
	}
	//console.log(table_data);
	document.getElementById("tbody").innerHTML = table_data;
}

function getData() {
	fetch(api_url)
	.then((response) => response.json())
	.then((data) => { 
		console.table(data); 
		loadData(data);
	});
}


function getDataById(id) {
	fetch(`${api_url}/get_one_record?id=${id}`)
	.then((response) => response.json())
	.then((data) => { 
	
		console.log(data);
		document.getElementById("id").value = data.id;
		document.getElementById("name").value = data.name;
		document.getElementById("age").value = data.age;
		document.getElementById("city").value = data.city;
	})
}


function postData() {
	var name = document.getElementById("name").value;
	var age = document.getElementById("age").value;
	var city = document.getElementById("city").value;
	
	data = {name: name, age: age, city: city};
	
	fetch(api_url, {
		method: "POST",
		headers: {
		  'Accept': 'application/json',
		  'Content-Type': 'application/json'
		},
		body: JSON.stringify(data)
	})
	.then((response) => response.json())
	.then((data) => { 
		console.log(data); 
		window.location.href = "index.html";
	})
}	


function putData() {
	
	var id = document.getElementById("id").value;
	var name = document.getElementById("name").value;
	var age = document.getElementById("age").value;
	var city = document.getElementById("city").value;
	
	data = {id: id, name: name, age: age, city: city};
	
	fetch(api_url, {
		method: "PUT",
		headers: {
		  'Accept': 'application/json',
		  'Content-Type': 'application/json'
		},
		body: JSON.stringify(data)
	})
	.then((response) => response.json())
	.then((data) => { 
		console.table(data);
		window.location.href = "index.html";
	})
}


function deleteData(id) {
	user_input = confirm("Are you sure you want to delete this record?");
	if(user_input) {
		//url = "http://localhost:8080/users?id=1234"
		
		fetch(`${api_url}?id=${id}`, {
			method: "DELETE",
			headers: {
			  'Accept': 'application/json',
			  'Content-Type': 'application/json'
			},
			body: JSON.stringify({"_id": id})
		})
		.then((response) => response.json())
		.then((data) => { 
			console.log(data); 
			window.location.reload();
		})
	}
}

index.html

<!DOCTYPE html>
<html>
	<head>
		<title>CIA Institute - Python Flask Project</title>
		<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" rel="stylesheet" crossorigin="anonymous">
		<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js"crossorigin="anonymous"></script>
	</head>
	<body class="d-flex flex-column h-100 container">
		<header>
			<nav class="navbar navbar-expand-lg navbar-expand-sm navbar-light bg-light">
			  <div class="container-fluid">
				<div class="collapse navbar-collapse" id="navbarNavAltMarkup">
				  <div class="navbar-nav">
					<a class="nav-link active" aria-current="page" href="#">Listing</a>
					<a class="nav-link" href="add.html">Add New</a>
				  </div>
				</div>
			  </div>
			</nav>
		</header>
		
		<table class="table table-striped table-hover text-center">
			<thead>
				<th>Name</th>
				<th>Age</th>
				<th>City</th>
				<th>Action</th>
			</thead>
			<tbody id="tbody">
				
			</tbody>
			<tfoot>
				
			</tfoot>
		</table>
		
		<footer class="footer mt-auto py-3 bg-light">
		  <div class="container text-center">
			<span class="text-muted"> &copy; CIA Institute 2023</span>
		  </div>
		</footer>
	</body>
	<script src="script.js"></script>
	<script>
		getData();
	</script>
</html>

add.html

<html>
	<head>
		<title>CIA Institute - Python Flask Project</title>
		<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" rel="stylesheet" crossorigin="anonymous">
		<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js"crossorigin="anonymous"></script>
	</head>
	<body class="d-flex flex-column h-100 container">
		<header>
			<nav class="navbar navbar-expand-lg navbar-expand-sm navbar-light bg-light">
			  <div class="container-fluid">
				<div class="collapse navbar-collapse" id="navbarNavAltMarkup">
				  <div class="navbar-nav">
					<a class="nav-link" href="index.html">Listing</a>
					<a class="nav-link active" aria-current="page" href="add.html">Add New</a>
				  </div>
				</div>
			  </div>
			</nav>
		</header>
		
		<h3>Add Document</h3>
		
		<form onsubmit="return false;">
		  <div class="mb-3">
			<label for="name" class="form-label">Name</label>
			<input type="text" class="form-control" id="name" autofocus>
		  </div>
		  <div class="mb-3">
			<label for="exampleInputPassword1" class="form-label">Age</label>
			<input type="text" class="form-control" id="age">
		  </div>
		  <div class="mb-3">
			<label for="city" class="form-label">City</label>
			<input type="text" class="form-control" id="city">
		  </div>
		  <button class="btn btn-primary" onclick="return postData()">Submit</button>
		  <a href="index.html" class="btn btn-primary">Cancel</a>
		</form>
		
		<footer class="footer mt-auto py-3 bg-light">
		  <div class="container text-center">
			<span class="text-muted"> &copy; CIA Institute 2022</span>
		  </div>
		</footer>
	</body>
	<script src="script.js"></script>
	<script>
	</script>
</html>

edit.html

<html>
	<head>
		<title>CIA Institute - Python Flask Project</title>
		<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" rel="stylesheet" crossorigin="anonymous">
		<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js"crossorigin="anonymous"></script>
	</head>
	<body class="d-flex flex-column h-100 container">
		<header>
			<nav class="navbar navbar-expand-lg navbar-expand-sm navbar-light bg-light">
			  <div class="container-fluid">
				<div class="collapse navbar-collapse" id="navbarNavAltMarkup">
				  <div class="navbar-nav">
					<a class="nav-link" href="index.html">Listing</a>
					<a class="nav-link active" aria-current="page" href="add.html">Add New</a>
				  </div>
				</div>
			  </div>
			</nav>
		</header>
		<h3>Edit Document</h3>
		<form onsubmit="return false;">
			<input type="hidden" class="form-control" id="id">
		  <div class="mb-3">
			<label for="name" class="form-label">Name</label>
			<input type="text" class="form-control" id="name" autofocus>
		  </div>
		  <div class="mb-3">
			<label for="exampleInputPassword1" class="form-label">Age</label>
			<input type="text" class="form-control" id="age">
		  </div>
		  <div class="mb-3">
			<label for="city" class="form-label">City</label>
			<input type="text" class="form-control" id="city">
		  </div>
		  <button class="btn btn-primary" onclick="return putData()">Update</button>
		  <a href="index.html" class="btn btn-primary">Cancel</a>
		</form>
		
		<footer class="footer mt-auto py-3 bg-light">
		  <div class="container text-center">
			<span class="text-muted"> &copy; CIA Institute 2022</span>
		  </div>
		</footer>
	</body>
	<script src="script.js"></script>
	<script>
		const urlParams = new URLSearchParams(window.location.search);
		const id = urlParams.get('id');
		getDataById(id);
	</script>
</html>