Transfer Vars Between Pydantic Instances

10 November 2022

Easily transfer attribute values from one pydantic model instance to another instance.

The Model

Let's say that you have a model and one instance:

>>> from pydantic import BaseModel
>>> class A(BaseModel):
...     field: str
...
>>> one = A(field="one")
>>> one 
A(field='one')

When you wanted to create another instance of the model, you could instatiate and then use the setters:

>>> two = A()
>>> two.field = one.field
>>> two
A(field='one')

Or you could set each field in the constructor:

>>> two = A(field=one.field)
>>> two
A(field='one')

But what if you have a model with twenty fields? This one-by-one copy is too tedious.

The good news is that you can splat all those 20 fields at once into the new instance.

Use vars() to create a dict of those fields and the ** splat to expand them all into kwargs for the class constructor:

>>> two = A(**vars(one))
>>> two
A(field='one')

Any other favorite methods for convenient copying?