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Heroku's Advantages Over Google App Engine


  • Postgres (you can even use pgAdmin to view your database)
  • Uses Git to push your application into production
  • More monitoring features and 3rd party apps
  • As long as your project uses one dyno, it runs for free (similar to google, but with a less confusing billing structure)
  • 10k row limit for your database before they start charging you $9 per month 

AttributeError: 'QuerySelectField' object has no attribute '_sa_instance_state'

I came across this error when I was trying to make a custom validator in Flask-Admin with wtforms form objects.

This code didn't work:
def location_must_not_conflict(form, field):
if Event.query.filter(Event.location == form.location).first():
raise wtforms.validators.ValidationError('Location conflicts with another request for the same venue.')

Because I was using form.location and not

This will work:
def location_must_not_conflict(form, field):
if Event.query.filter(Event.location ==
raise wtforms.validators.ValidationError('Location conflicts with another request for the same venue.')

Google Calendar Api bad request 400 - Python Authomatic Library

I was finally able to get the request to go through by adding a header saying it's json format. Here's an example:

requestbody = """
      "end": {
      "dateTime": "2014-05-18T01:35:00Z"
      "start": {
      "dateTime": "2014-05-18T01:35:00Z"
      "description": "test2",
      "location": "test venue",
      "summary": "test2"
response = authomatic.access(credentials, url, method='POST', headers={'Content-Type': 'application/json'}, body=requestbody)

Add user_id for modified_by field before save - Flask-Admin

In Flask-Admin, you can override the "on_model_change" function to to automatically populate a "modified_by" field in your model.

class LocationView(ModelView):
def on_model_change(self, form, model):
model.user_id =

admin = Admin(app)
admin.add_view(LocationView(Location, db.session, name="Locations"))

Favorite Flask Boilerplate/Skeleton/Templates

Those do a lot of the work of starting a new Flask project for you.

With cookiecutter flask, all you need to do to build a new project is: cookiecutter

As a warning, cookiecutter flask and overholt include a lot of stuff. I ended up not using it because it was too much work to change everything to work with oAuth.

Reverse PDF Page Order

I created an app that allows you to upload a pdf and it returns a copy of your PDF with the page order reversed. The code is here:

Initially when I googled how to do this in Adobe Acrobat, the first few results had fairly complicated solutions. After I made the app, I ended up finding an easier way to do it in Adobe (in the 6th from the top Google result on “reverse pdf order acrobat”…):

Oh well, it was a fun project.

Discourse As Potential Mailing List Replacement

While tested out Discourse, I only found a few negative things:

  1. To make it act like a mailing list, it currently requires each user to change settings on their account:
    I commented on a thread about a new feature that allows setting defaults for this:
  2. It doesn’t allow setting defaults for which categories the user has “Watched”. For example, I would want to default the “General” list to “Watched”, but more obscure lists would only be watched if the user chooses to.
  3. It uses a different e-mail address for each e-mail it sends you (this is to keep track of which thread it belongs to), here’s an example of a “From” address:
    Google Groups always has the same to/from e-mail address and magically figures this out. This might be weird in some peoples’ email clients.

As a forum, this beats the crap out of PhpBB, but as a mailing list it’s not a clear winner over Google Groups yet. It’s open source, has a better web interface, and the “Categories” are a cool feature for keeping all the lists in the same place. But, the “email in” functionality was too recently implemented, and it might take a few months before it’s as polished as Google Groups.

It’s going to be a very tempting replacement if they add default settings for user preferences.


discourse 1

discourse 2

discourse 3

discourse 4

discourse 5

Data source name not found and no default driver specified - SQLalchemy/Sybase

I was getting this error when trying to connect to a sybase database using Microsoft's odbc driver by using the connection string shown in the SqlAlchemy examples:
DBAPIError: (Error) ('IM002', '[IM002] [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified (0) (SQLDriverConnect)') None None

The following code worked to connect:
import pyodbc, sqlalchemy

def connect():
    return pyodbc.connect('DSN=<dsn name>;UID=<username>;PWD=<password>')

srcEngine = sqlalchemy.create_engine('sybase+pyodbc://', creator=connect, echo=True)