Generate QR Code Using Google Charts API

Here's a small utility to generate QR code image using Google Charts API.

Note the hand crafted Python 2/3 support, for more advanced stuff you might want to have a look at six. However for this script I wanted to stay without external dependencies.

Common Errors

"Experience is the name every one gives to their mistakes."

    - Oscar Wilde

Students are sometimes amazed by how I can tell the cause of exception without looking at the code. This is the result of making many errors in Python myself and also from observing many students doing mistakes. Here's a short list I've compiled of most likely cause of errors:

NameError

• You forgot to import a module
• You made a typo

AttributeError: 'NoneType' object has no attribute ...

• You forgot a return in your function

AttributeError

• Typo on dot lookup (obj.foo)
• Object is different type from what you think (str vs int)
• Object does not implement a dunder method (e.g. __len__)

There's also the 3'rd party didyoumean module, which might be interesting for beginners. It changes the default stack trace to add a hint about what might be the problem.

A Streaming Chart using Flask and flot

I was teaching a course on "Python Analytics" (pandas, scikit-learn, matplotlib ...) and was asked to provide an example of streaming chart - ones that updates periodically. I''ve showed a couple of examples one by generating image using matplotlib and another with bokeh-server. After a couple of days I remembered another way - using flot to render the chart. Here''s a small example using Flask as the web server (the code works both on Python 2 and 3).


Few comments:

• Don''t use debug=True in production :)
• For simplicity everything is in one file. However for larger application you might want to take the HTML template(s) out
• Data is in memory, a restart will wipe it out. If you need data persistence - pick a database (shelve, sqlite3 ...)
• A big shoutout to Continuum Analytics - Anaconda (and conda) has made my life so much easier teaching this workshop.