Python typing error when incrementing a dict value: 'Unsupported operand types for + ("object" and "int")'

Question

I have this code:

result = {"AAA": "a", "BBB": "b", "Count": 0}
result["Count"] += 1

mypy generates this error message:

Unsupported operand types for + ("object" and "int")

What are some easy ways to fix this?

Answer 1

You can define the expected shape of the dictionary by defining a TypedDict:

from typing import TypedDict

class ResultDict(TypedDict):
    AAA: str
    BBB: str
    Count: int

result: ResultDict = {"AAA": "a", "BBB": "b", "Count": 0}
result["Count"] += 1

In practice, it's generally easier to use a dataclasses.dataclass when you want to collect different types of data under specific names in a single object in a type-safe way. The syntax looks different but you get essentially the same functionality:

from dataclasses import dataclass

@dataclass
class Result:
    AAA: str
    BBB: str
    Count: int

result = Result(AAA="a", BBB="b", Count=0)
result.Count += 1