Building simple web services application with Flask

Flask is a framework for building WSGI applications. 

pip install flask

download postman www.postman.com/product/rest-client/

Let's start with building a simple Hello World application


ROUTING

Use the route() decorator to bind a function to a URL

from flask import Flask

#create a Flask application
#the argument to Flask is the name of the application's module
#since we are running our application in a single file, leave it as __name__
app=Flask(__name__)

#relative path to the root of your application
@app.route('/')
def hello_world():
    return 'Hello World!'

app.run()

from flask import Flask

app=Flask(__name__)

@app.route('/input')
def input():
    return 'receive input here'

@app.route('/output')
def output():
    return 'display output here'

app.run()

Let's display a meaningful data as part of our output - GET method

from flask import Flask, jsonify

app=Flask(__name__)

data=[{'fname':'Steve', 'lname':'Jobbs'},{'fname':'Bill', 'lname':'Gates'}]

@app.route('/input')
def input():
	return 'input here'

@app.route('/data', methods=['GET'])
def get_data():
	return jsonify({'data' : data})

app.run(debug = True)

You can JSONinfy any combination of maps and lists, however the top outer collection cannot be a list.

You can use the URL path to pass the data to the function call:

from flask import Flask, jsonify
from markupsafe import escape

app=Flask(__name__)

data=[{'fname':'Steve', 'lname':'Jobbs'},{'fname':'Bill', 'lname':'Gates'}]

@app.route('/input')
def input():
	return 'input here'

@app.route('/data', methods=['GET'])
def get_data():
	return jsonify({'data' : data})

@app.route('/data/<int:id>', methods=['GET'])
def get_data_byid(id):
	return jsonify({'data' : data[id]})

@app.route('/data/<key>/<value>', methods=['GET'])
def get_data_byname(key, value):
	for item in data:
		if item[escape(key)] == escape(value):
			return jsonify({'data' : item})

app.run(debug = True)

Converter Types

Templating

Flask uses Jinja for templating
Flask will look for templates in the templates folder. ​

from flask import Flask
from flask import render_template

app=Flask(__name__)

@app.route('/hello/')
@app.route('/hello/<name>')
def hello(name=None):
    return render_template('hello.html', name=name)

app.run(debug = True)

​html in the templates/hello.html file

<title>Hello HTML</title>
{% if name %}
  <h1>Hello {{ name }}!</h1>
{% else %}
  <h1>Hello, World!</h1>
{% endif %}

​Creating POST methods:

from flask import Flask, jsonify, request, abort

app=Flask(__name__)

data=[{'fname':'Steve', 'lname':'Jobbs'},{'fname':'Bill', 'lname':'Gates'}]

@app.route('/createperson', methods=['POST'])
def create_person():
	print(request.json)
	if not request.json or not 'person' in request.json:
		abort(400)
	data.append(request.json['person'])
	return jsonify({'data' : data}), 201

@app.route('/data', methods=['GET'])
def get_data():
	return jsonify({'data' : data})

@app.route('/data/', methods=['GET'])
def get_data_byid(id):
	return jsonify({'data' : data[id]})

app.run(debug = True)

​Sample POSTMAN request

http://127.0.0.1:5000/createperson

{"person":{"fname":"sergey", "lname":"brin"}}

Processing GET (Query) parameters:

from flask import Flask, jsonify, request, abort

app=Flask(__name__)

data=[{'fname':'Steve', 'lname':'Jobbs'},{'fname':'Bill', 'lname':'Gates'}]

@app.route('/createperson', methods=['POST'])
def create_person():
	print(request.json)
	if not request.json or not 'person' in request.json:
		abort(400)
	data.append(request.json['person'])
	return jsonify({'data' : data}), 201

@app.route('/search', methods=['GET'])
def search_data():
	query = request.args.get('query', '')
	for item in data:
		if item['fname'] == query or item['lname'] == query:
			return jsonify({'data' : [item]})
	return jsonify({})

@app.route('/data', methods=['GET'])
def get_data():
	return jsonify({'data' : data})

@app.route('/data/', methods=['GET'])
def get_data_byid(id):
	return jsonify({'data' : data[id]})

app.run(debug = True)

​Processing Images with Web Services

from flask import Flask, send_file, request, abort, make_response
from PIL import Image
from PIL import ImageFilter

app=Flask(__name__)

@app.route('/processimage', methods=['POST'])
def processimage():
	f = request.files['file']
	im = Image.open(f)
	im = im.filter(ImageFilter.BLUR)
	im.save("images/site.png")
	return send_file("images/site.png", mimetype='image/png')
	
app.run(debug = True)

​file 

mario_png64.png
File Size:	4721 kb
File Type:	png

Download File

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Handling Session

from flask import Flask, session, redirect, url_for, request
from markupsafe import escape

app = Flask(__name__)

# Set the secret key to some random bytes. Keep this really secret!
app.secret_key = b'_5#y2L"F4Q8z\n\xec]/'

@app.route('/')
def index():
    if 'username' in session: #session object is provided to you, like request
        return 'Logged in as {}'.format(escape(session['username'])) 
    return 'You are not logged in'

@app.route('/login', methods=['GET', 'POST'])
def login():
    #this part is executed after the submit
    if request.method == 'POST':  
        session['username'] = request.form['username']
        #url_for can be used to reverse-lookup the url for a method
        return redirect(url_for('index')) 
    #by default the submit button will submit into the same URL
    #and come back as a form POST request
    return '''
        <form method="post">
            <p><input type=text name=username>
            <p><input type=submit value=Login>
        </form>
    '''

@app.route('/logout')
def logout():
    # remove the username from the session if it's there
    session.pop('username', None)
    return redirect(url_for('index'))

app.run(debug = True)