Set dataclass variable to double the default value

This is probably too much of a perfectionist question but.. I'd like to instantiate a dataclass with double the default value. So that if I change the default value, instantiating it will provide double the usual default. I'm hoping there is a better way to do this than simply reading and updating the values.

Here is a simple example to explain what I want:

from dataclasses import dataclass

@dataclass
class Value:
    variable1: int = 1
    variable2: int = 2
    variable3: int = 3    

value = Value()
doubled_value = Value() {* 2 for all}

print(value.variable1)
print(value.variable2)
print(value.variable3)

print(doubled_value.variable1)
print(doubled_value.variable2)
print(doubled_value.variable3)

>>> 1
>>> 2
>>> 3

>>> 2
>>> 4
>>> 6

This works but is hard to understand and ugly:

from dataclasses import dataclass

@dataclass
class Value:
    variable1: int = 1
    variable2: int = 2
    variable3: int = 3    

value = Value()
doubled_value = Value()

for i, var in enumerate(doubled_value.__dataclass_fields__.items()):
    doubled_value.__setattr__(var[0], var[1].default*2)

print(value.variable1)
print(value.variable2)
print(value.variable3)

print(doubled_value.variable1)
print(doubled_value.variable2)
print(doubled_value.variable3)

>>> 1
>>> 2
>>> 3

>>> 2
>>> 4
>>> 6

To be clear, I want it to work regardless of default value so doubled_value = Value(2, 4, 6) won't work

Thank you for any help. This is my first post on stack overflow so please let me know if I've made any mistakes.

Solution

Are you looking for something like this?

from dataclasses import dataclass, fields

@dataclass
class Value:
    variable1: int = 1
    variable2: int = 2
    variable3: int = 3    

    @classmethod
    def times(cls, times=2):
        return cls(*(f.default * times for f in fields(cls)))

value = Value()
doubled_value = Value.times()
tripled_value = Value.times(3)

fields allows you to obtain a list of fields and their default values, which I'm simply multiplying in a generator expression, which is unpacked to arguments to the class.