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Archive for October, 2020

Quick Python Flask

without comments

A quick example of installing and running a sample hello.py file with the Flask application with the Command Line Interface (CLI) documentation on the Flask website. The first thing you need to do is install the flask module with the pip3 utility on Fedora Linux (or most other platforms):

pip3 install flask --user student

You should see a successful log like this for student user:

Requirement already satisfied: flask in /usr/local/lib64/python3.7/site-packages (1.1.2)
Collecting student
  Downloading https://files.pythonhosted.org/packages/b5/af/be416c18e4fe63a582e06fb0d47bf059bd0f4f413e5a6cfe893747ebaf79/Student-0.0.1-py3-none-any.whl
Requirement already satisfied: click>=5.1 in /usr/lib/python3.7/site-packages (from flask) (7.1.1)
Requirement already satisfied: itsdangerous>=0.24 in /usr/local/lib/python3.7/site-packages (from flask) (1.1.0)
Requirement already satisfied: Werkzeug>=0.15 in /usr/local/lib/python3.7/site-packages (from flask) (1.0.1)
Requirement already satisfied: Jinja2>=2.10.1 in /usr/lib/python3.7/site-packages (from flask) (2.10.1)
Requirement already satisfied: MarkupSafe>=0.23 in /usr/lib64/python3.7/site-packages (from Jinja2>=2.10.1->flask) (1.1.1)
Installing collected packages: student
Successfully installed student-0.0.1

The smallest footprint hello.py program is:

# Import statement.
from flask import Flask
 
# Application defintion.
app = Flask(__name__)
 
# Basic URI rotuing.
@app.route("/")
 
# Define a hello function.
def hello():
  return "Hello World!"
 
# Run the program.
if __name__ == "__main__":
  app.run()

You can run the program from the command line with two commands:

export FLASK_APP=hello.py
flask run

It will show you the following in the terminal session:

 * Serving Flask app "hello.py"
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Type the following URL in a local browser:

http://localhost:5000/

Flask will add the following to the console log:

127.0.0.1 - - [26/Oct/2020 00:37:49] "GET / HTTP/1.1" 200 -

You can jazz the hello.py program up with a an argument list, like this modified example based on this comparison article on Python frameworks:

# Import libraries.
from flask import Flask, escape, request
 
# Define the application.
app = Flask(__name__)
 
# Define a base URI route and function.
@app.route('/')
def index():
  return "Index Page"
 
# Define an application URI route and function.
@app.route("/hello")
def hello():
  name = request.args.get("name","Simon")
  return f'Hello {escape(name)}!'
 
# Define an about URI route and function.
@app.route("/about")
def about():
  return "About Page"
 
# Run the file.
if __name__ == "__main__":
  app.run()

It prints 'Hello Simon!' in a web page. If you try to stop your Flask server with a Ctrl+Z instead of a Ctrl+C, the next time you go to start it you will receive an error message like:

OSError: [Errno 98] Address already in use

You’ll need to find the Linux process ID and kill the process with prejudice. You can find the process with the following Linux command:

sudo netstat -nlp | grep 5000
[sudo] password for student:

It prompts you for your sudoer password, and then returns a line like:

tcp        0      0 127.0.0.1:5000          0.0.0.0:*               LISTEN      76802/python3

You kill the process with the following Linux command:

kill -9 76802

As always, I hope this helps those looking for the missing pieces.

Written by maclochlainn

October 26th, 2020 at 12:54 am

Posted in Fedora,Linux,Python,Python 3.x

Tagged with

MySQL Floating Types

with 2 comments

I’m glad that testing new MySQL releases is so frequent for me. Each testing cycle let me catch warning messages about deprecated behaviors before they’re removed. This one announced the deprecation of digits for floating point data types, like double. The following column definition for a table in my code tree triggered the warning message:

, amount                DOUBLE(10,2)

MySQL 8 (8.0.21) raised the following warning message:

Warning (code 1681): Specifying number of digits for floating point data types is deprecated and will be removed in a future release.

Recognizing the deprecation, I redefined the column as:

, amount                DOUBLE

I’m glad the MySQL development team is focused on alerting us to deprecations through warning messages. Naturally, I fixed all of the tables proactively. If you want more detail you can read this MySQL web page on Problems with Floating Point Values.

Written by maclochlainn

October 8th, 2020 at 12:06 pm

Posted in MySQL,MySQL 8,sql

Tagged with ,