I’ve been working on an IOT project using a Raspberry PI Zero W. I fully intend to document it here in a future post, so I won’t go into details about it now.
This post came about because I was troubleshooting a problem and the root cause surprised me.
I come from the world of C#/Java/Swift and part of the reason for taking on this project was learning a new language. The code for this device is written in Python.
Python has OOP structures like the aforementioned languages and I expected similar behavior. The OOP mantra, of course is, Encapsulation, Inheritance, Polymorphism.
From my reading it seems that Python doesn’t have the same idea of private/public as other languages making the first principle a bit fuzzy.
I have a class with quite a few class variables. This class is instantiated multiple times and I fully expected that the variables from each instantiation would be distinct. However, in this case, one of them was not.
I have code that looks like this:
class myClass: myData =  * 100
Later I fill the array with data.
What I discovered was that apparently all of the arrays were mapped to the same address space. I only had one copy of the data and was overwriting it in each class instance. As I was expecting each to be unique, this was not the desired behavior.
The solution was simple, I moved the initialization into the class __init:
def __init(self, vars...): self.myData =  * 100
It now works as expected, but it took quite a while to drill down to the root cause.
StackOverflow question here.