How to loop through dataclass in Python?

Question

I would like to loop through a dataclass in python, to find all cars, which fit a certain criteria, however, the code never works, because the variable gets interpreted as an attribute, and not a variable.

from dataclasses import dataclass

@dataclass
class cars:
    year: int = 0
    model: str = "unknown"
    PS: int = 0
    colour: str = "unknown"

car_1 = cars(year = 1980, colour = "brown")
car_2 = cars(year = 1999, colour = "black", PS = 82)

owned_cars = [car_1, car_2]

criteria = input("Which criteria to search for? year, model, PS, colour")

for car in owned_cars:
    value = car.criteria
    print(value, car)

AttributeError: 'cars' object has no attribute 'criteria'

When using:

value = car.year

the code runs fine. How can I tell python, it should interpret criteria as the variable and use its content, instead of its name?

I'd try to type in `__dict__` if I were a user of that program... — jbndlr, Oct 23 '19 at 18:51

score 2 · Accepted Answer · edited Oct 23 '19 at 18:49

2

This doesn't have anything to do with car being a dataclass. It's just how Python attributes work. If you want to look up an attribute by its name in a string, use getattr:

value = getattr(car, criteria)

edited Oct 23 '19 at 18:49

Brown Bear

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answered Oct 23 '19 at 18:47

Blckknght

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not an answer, and not a duplicate but great Q. – droid192 Apr 27 '20 at 14:02
2

@qrtLs: I'm not sure what you mean by that. This answers how to turn a string like `"year"` into an attribute lookup equivalent to `car.year`, which was what the questioner wanted (as judged by their choice to accept this answer). It may be that you have some other issue you should ask about separately. – Blckknght Apr 27 '20 at 22:11

How to loop through dataclass in Python?

1 Answers1