How can I invert `dataclass.astuple`?

Question

I am trying to construct a hierarchy of dataclasses from a tuple, like so:

from dataclasses import astuple, dataclass

@dataclass
class Child:
    name: str

@dataclass
class Parent:
    child: Child

# this is what I want
p = Parent(Child("Tim"))
print(p)

# this is what I get
t = astuple(p)
print(Parent(*t))

However, while this constructs a Parent as expected, its child is not of type Child:

Parent(child=Child(name='Tim'))
Parent(child=('Tim',))

Is there a way to construct Parent and child from the tuple t, or by some other means?

Answer 1

You can use a helper function that constructs an instance of a dataclass from a given tuple of values and recursively constructs child instances for fields that are dataclasses:

from dataclasses import astuple, dataclass, fields, is_dataclass

@dataclass
class Child:
    name: str

@dataclass
class Parent:
    child: Child

def from_tuple(cls, data):
    return cls(*(
        from_tuple(type, obj) if is_dataclass(type := field.type) else obj
        for obj, field in zip(data, fields(cls))
    ))

p = Parent(Child("Tim"))
t = astuple(p)
print(from_tuple(Parent, t))

This outputs:

Parent(child=Child(name='Tim'))

Demo here