Jeremy Satterfield
Coding, Brewing and Tulsa Life

Keeping MRO In Mind When Mocking Inherited Methods

So I just spent a couple of hours banging my head on a ridiculous PyMox mocking issue and though I'd share. Here is an example of the existing code.

Mocking a property in Python

Anytime I see someone turning an instance method into a property on a Python object, I always have to step back and rethink whether it's really the right thing to do. While properties certain have valid use cases, I often see them overused and misused. This can result in code that is harder to refactor should you decide you actually do want to accept arguments as well as less straight forward to separate in unit tests.

Class-based Celery Tasks

Update 2017-11-02: Celery 4 now adivises against inheriting from Task unless you are extending common functionality. However you can still get similar functionality by creating a new class and calling is from inside a decorated function task.

Mocking Python's built-in open function

A while back I was working on my podcast client and ran into an issue downloading large files. The root problem was that all of Django's FileField backends store the file (or file-like object) to memory then saves it to disk, and the cubieboard system I was using had limitied memry resources, resulting in "out of memory" errors. After much searching and hacking I finally settled on just storing the file to disk myself using requests streaming argument. This allowed me to download the file in chunks and save directly to disk and then tell the Django field where I placed it, as you can see here.

Abusing Django Rest Framework Part 4: Object-level field exclusion

Similar to the object-level readonly field from my previous post, there are some cases where we want to exclude certain fields based on what object the user is trying to access. You could overwrite the views get_serializer method to use a different serializer based on their access, but if nesting serializers is a possiblility this get messy, somewhere in the neighborhood of O(n2). Another option is to modify a serializers to_native method.