As you can see from the latest updated code –
self.changes = {"MTMA",123}
When you define self.changes as above , you are actually defining a set , not a dictionary , since you used ‘,’ (comma) instead of colon , I am pretty sure in your actual code you are using comma itself , not colon .
To define a dictionary with “MTMA” as key and 123 as value , use a colon in between them , Example –
self.changes = {"MTMA":123}
Do similarly in your actual code as well.
If what you want is an empty dictionary , define it as –
self.changes = {}