Develop Reference

Flask webapp as user interface for a python module

I have written a python module for extracting archives and processing some data from the extracted files, then optionally deleting the extracted files. Currently I am using it by writing user-code in a separate python script. e.g:
import my_module
with my_module.archive("data.rar") as a:
a.extract()
a.convert("data.csv", "data.xlxs")
a.delete(keep="data.xlsx")
But for non-programmers to use it, I am trying to create a webapp user-interface for it with flask.
What are the best practices for implementing some communication between the user and the module through a webapp? For example
how could my module to communicate to the webapp-user that the extraction or the data processing has finished?
how should the it display the list of extracted files?
how could the user select a file to be processed or to be deleted?
Basically I need to interleave my library code with some user code and I would like the webapp to generate and execute the user-code and to display the output of the processing module.

(I sense a close flag coming since this is a broad topic and it's been a while since "best practices" topics were allowed on SO. )
Based on my on faults I'd recommend to:
implement the backend first, don't waste time on web design if the backend functionality is not crystal clear yet. Read about flask blueprints and create a blueprint for all public calls like list directory, select file, unzip file, etc... test it out, use requests, post stuff, check responses, iterate.
if you are satisfied with basic functionality, start implementing the frontend. For interactivity you can use the very same api calls via javascript you already tested, use XMLHttpRequest (or use jQuery - I am not a big fan of that) for posting stuff. The catch here is that when you post (from the browser), you can define a callback, so you may use the flask response to update the interface.
add some css, eventlisteners to your templates to make it pretty and comfy.
Get ideas from here and here and here and here (just googled for some random pages, some seemed on topic for you).
You probably want to read this too.

How to turn a simple python script to basic webapp?

I would like to know what is the fastest way to turn a simple Python script into a basic web app.
For example, say I would like to create a web app that takes a keyword from the user and display the most retweeted tweet on Twitter. If I write a python script that is capable of performing that task using Twitter's API, how would I go about turning it into a web app for people to access?
I have looked at frameworks such as Django, but it would take me weeks or months to learn how to use it. I just need something quick and simple. Any such alternatives?

Make a CGI script out of it. You basically get the request information from the webserver via environment variables and you print the desired HTML to stdout. There are helper libraries such as Werkzeug which help with abstracting away the handling of the environment variables by wrapping them in a Request object.
This technique is quite outdated and isn't normally used nowadays as the script has to be run on every request and thus incurs the startup cost all the time.
Nevertheless this may actually be a good solution for you because it is quick and every webserver supports it.

Is it possible to run a Python app on a WordPress site?

I have an idea for a web app and plan to learn Python as I go (right now I know html/css, some javascript, some php and sql). The app would be able to manipulate and analyze audio files, among other things.
Ideally, I'd like to make the app available through my wordpress site so that I can take advantage of WordPress's login management and the plugin s2member's subscription management and content restriction capabilities.
Is that possible? Would it even make sense?
If not, is there a better alternative to automate all of that (the subscription management, logins, payment processing, content restriction, etc) without having to code it myself?

I suggest you develop a REST API in Python and extend your Wordpress site to consume that API.
For the Python side, you could go with Flask and use Flask-RESTful.
For the Wordpress side, have a look at this question.

Sure, if you meet a couple of conditions:
The server your wordpress site is on also has python
And you have the ability run arbitrary python scripts on said server.
Here's a (very contrived) example of how to do it from a plugin:
call-python.php (plugin file):
<php
/*
Plugin name: Call Python
Author:..
....
*/
$pyScript = "/path/to/app.py";
exec("/usr/bin/python $pyScript", $output);
var_dump($output);
And the python script app.py:
print("Hello, World")
And that's it! That will dump Hello, world to the body. Obviously you'll need a bit more for a more complicated python app, but it will work.
Like others are saying, there may be better "more correct" ways of doing it. But if your end goal is to run a python app from WordPress it's possible.

Is there a production-safe way to measure time spent in Production w/Python?

I want to be able to instrument Python applications so that I know:
Page generation time.
Percentage of time spent in external requests (mysql, api calls).
Number of mysql queries, what the MySQL queries were.
I want this data from production (not offline profiling) - because the time spent in various places will be different under load.
In PHP I can do this with XHProf or instrumentation-for-php. In Ruby on Rails/.NET/Java, I can do this with New Relic.
Is there such a package recommended for Python or django?

Yes, it's perfectly possible. E.g. use some magic switch in URL, like "?profile-me" which triggers profiling in Django middleware.
There are a number of snippets on the Internet, like this one: http://djangosnippets.org/snippets/70/ or modules like this one: http://code.google.com/p/django-profiling/ - but I haven't used any of them so I cannot recommend anything.
Anyway, the approach they take is similar to what I do - i.e. use Python Hotshot profiler module in a middleware that wraps your view. For the MySQL part, you can just use connection.queries form Django.
The nice thing about Hotshot is that its output can be browsed using Kcachegrind like here: http://www.rkblog.rk.edu.pl/w/p/django-profiling-hotshot-and-kcachegrind/

New Relic now had a package for Python, including Django through mod_wsgi.
https://support.newrelic.com/help/kb/python

django-prometheus is a good choice for handling production workloads, especially in a container environment like Kubernetes. Out of the box, it has middleware for tracking request latencies and counts (by view method), as well as Database and cache access times. It wouldn't be a good solution for tracking which queries are actually executing, but that's where a logging solution like ELK would come into play. If it helps, I've written a post which walks through how to add custom metrics to a Django application.

Is it possible to write dynamic web pages in Python with the Really Simple HTTP Server?

I know that with the SimpleHTTPServer I can make my directories accessible by web-browsers via Internet. So, I run just one line of the code and, as a result, another person working on another computer can use his/her browser to see content of my directories.
But I wander if I can make more complicated things. For example, somebody uses his/her browser to load my Python program with a set of parameter (example.py?x=2&y=2) and, as a result, he/she sees the HTML page generated by the Python program (not the Python program).
I also wander if I can process html form submitted to the SimpleHTTPServer.

While it is possible, you have to do pretty much everything yourself (parsing request parameters, handle routing, etc).
If you are not looking to get experience in creating web-frameworks, but just want to create a small site you should probably use a minimalistic framework instead.
Try Bottle, a simple single-file web framework: http://bottlepy.org

Maybe the VerseMatch project and related recipes over at ActiveState is something you would be interested in examining? It implements a small application using the standard library for dynamic running.

have you considered using CGIHTTPServer instead of SimpleHTTPServer? Then you can toss your scripts in cgi-bin and they'll execute. You have to include content-type header and whatnot but if you're looking for quick and dirty it's real convenient