Introduction
Welcome to this journey into the world of web servers and the Flask framework! In the previous weeks, you’ve successfully set up a web server using GitHub Pages, converting Jupyter Notebooks into Markdown for a seamless online presentation. Today, we’ll take that knowledge to the next level as we dive into creating your very own web server using Flask.
Understanding Web Servers
What is a Web Server?
Traditionally, we had librarians at libraries that would help you find books or information. Today in the digital world, thousands upon thousands of home pages, search engines, and digital archives have been built using web servers.
GitHub Pages vs. Flask
You’ve already experienced a form of web server through GitHub Pages. Think of GitHub Pages as a library that has established rules for publishing Markdown notes and Jupyter Notebooks neatly on a bookshelf.
Now, let’s introduce Flask, your personal web server. Flask can create and manage any type of content, including customizing everything according to your preferences, and even serve additional information (like a database with APIs).
The Flask Framework Flask is a micro web framework written in Python. It’s designed to be minimal and easy to use, making it perfect for building web applications, APIs, and, yes, even your web server. Today, we will start with the basics of Flask and see how it empowers you to create and manage web content.
Our Goals for Today
Here’s what we’ll accomplish in this session:
- Create a minimal Flask server.
- Explore the Python/Flask process.
- Access data from our Flask server using Python.
- Access data from our Flask server using JavaScript.
- Learn how to stop the Python/Flask process gracefully.
Note: Jupyter magic commmand %%python --bg
that follows runs the server in background. This enables us to continue interacting with the subsequent Notebook cells.
%%python --bg
from flask import Flask, jsonify
from flask_cors import CORS
from werkzeug.serving import run_simple
# initialize a flask application (app)
app = Flask(__name__)
CORS(app, supports_credentials=True, origins='*') # Allow all origins (*)
# ... your existing Flask
# add an api endpoint to flask app
@app.route('/api/data')
def get_data():
# start a list, to be used like a information database
InfoDb = []
# add a row to list, an Info record
InfoDb.append({
"FirstName": "John",
"LastName": "Mortensen",
"DOB": "October 21",
"Residence": "San Diego",
"Email": "jmortensen@powayusd.com",
"Owns_Cars": ["2015-Fusion", "2011-Ranger", "2003-Excursion", "1997-F350", "1969-Cadillac"]
})
# add a row to list, an Info record
InfoDb.append({
"FirstName": "Shane",
"LastName": "Lopez",
"DOB": "February 27",
"Residence": "San Diego",
"Email": "slopez@powayusd.com",
"Owns_Cars": ["2021-Insight"]
})
return jsonify(InfoDb)
# add an HTML endpoint to flask app
@app.route('/')
def say_hello():
html_content = """
<html>
<head>
<title>Hellox</title>
</head>
<body>
<h2>Hello, World!</h2>
</body>
</html>
"""
return html_content
if __name__ == '__main__':
# starts flask server on default port, http://127.0.0.1:5001
run_simple('localhost', 5001, app)
Show Python/Flask process
This script discovers the running flask process
%%script bash
# After app.run(), see the the Python process
lsof -i :5001
# see the the Python app
lsof -i :5001 | awk '/Python/ {print $2}' | xargs ps
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
python 20158 iwu88 3u IPv4 3866493 0t0 TCP localhost:5001 (LISTEN)
PID TTY TIME CMD
3335 pts/1 00:00:01 python
3336 pts/1 00:00:02 node
3337 pts/1 00:02:59 node
3360 pts/1 00:00:00 node
15738 pts/1 00:00:02 python
20147 pts/1 00:00:00 python
20158 pts/1 00:00:00 python
20160 pts/1 00:00:00 bash
20164 pts/1 00:00:00 xargs
20165 pts/1 00:00:00 ps
26555 pts/1 00:00:00 sh
26556 pts/1 00:00:00 sh
26561 pts/1 00:00:00 sh
26565 pts/1 00:01:18 node
26594 pts/1 00:00:15 node
26644 pts/1 00:21:21 node
26672 pts/1 00:01:35 node
26720 pts/1 00:00:06 node
26789 pts/1 00:08:45 node
26865 pts/1 00:00:23 node
27013 pts/1 00:00:00 python
27036 pts/1 00:00:04 node
your 131072x1 screen size is bogus. expect trouble
Access API with Python
This script extracts data from Web Server.
import requests
res = requests.get('http://127.0.0.1:5001/api/data')
res.json()
[{'DOB': 'October 21',
'Email': 'jmortensen@powayusd.com',
'FirstName': 'John',
'LastName': 'Mortensen',
'Owns_Cars': ['2015-Fusion',
'2011-Ranger',
'2003-Excursion',
'1997-F350',
'1969-Cadillac'],
'Residence': 'San Diego'},
{'DOB': 'February 27',
'Email': 'slopez@powayusd.com',
'FirstName': 'Shane',
'LastName': 'Lopez',
'Owns_Cars': ['2021-Insight'],
'Residence': 'San Diego'}]
Access API with JavaScript
This code extracts data “live” from a local Web Server with JavaScript fetch. Additionally, it formats the data into a table.
First Name | Last Name | Residence |
---|
Kill Python/Flask process
This script ends Python/Flask process
%%script bash
lsof -i :5001 | awk '/Python/ {print $2}' | xargs kill -9
Usage:
kill [options] <pid> [...]
Options:
<pid> [...] send signal to every <pid> listed
-<signal>, -s, --signal <signal>
specify the <signal> to be sent
-q, --queue <value> integer value to be sent with the signal
-l, --list=[<signal>] list all signal names, or convert one to a name
-L, --table list all signal names in a nice table
-h, --help display this help and exit
-V, --version output version information and exit
For more details see kill(1).
---------------------------------------------------------------------------
CalledProcessError Traceback (most recent call last)
/tmp/ipykernel_20147/1062927812.py in <module>
----> 1 get_ipython().run_cell_magic('script', 'bash', "\nlsof -i :5001 | awk '/Python/ {print $2}' | xargs kill -9\n")
/usr/lib/python3/dist-packages/IPython/core/interactiveshell.py in run_cell_magic(self, magic_name, line, cell)
2417 with self.builtin_trap:
2418 args = (magic_arg_s, cell)
-> 2419 result = fn(*args, **kwargs)
2420 return result
2421
<decorator-gen-103> in shebang(self, line, cell)
/usr/lib/python3/dist-packages/IPython/core/magic.py in <lambda>(f, *a, **k)
185 # but it's overkill for just that one bit of state.
186 def magic_deco(arg):
--> 187 call = lambda f, *a, **k: f(*a, **k)
188
189 if callable(arg):
/usr/lib/python3/dist-packages/IPython/core/magics/script.py in shebang(self, line, cell)
243 sys.stderr.flush()
244 if args.raise_error and p.returncode!=0:
--> 245 raise CalledProcessError(p.returncode, cell, output=out, stderr=err)
246
247 def _run_script(self, p, cell, to_close):
CalledProcessError: Command 'b"\nlsof -i :5001 | awk '/Python/ {print $2}' | xargs kill -9\n"' returned non-zero exit status 123.
Hacks
Edit, stop and start the web server.
- Add to the Home Page
- Add your own information to the Web API
- Use from Template to start your own Team Flask project https://github.com/nighthawkcoders/flask_portfolio