Loading Pydantic models from JSON without running out of memory

You have a large JSON file, and you want to load the data into Pydantic.
Unfortunately, this uses a lot of memory, to the point where large JSON files are very difficult to read.
What to do?

Assuming you’re stuck with JSON, in this article we’ll cover:

• The high memory usage you get with Pydantic’s default JSON loading.
• How to reduce memory usage by switching to another JSON library.
• Going further by switching to dataclasses with slots.

The problem: 20× memory multiplier

We’re going to start with a 100MB JSON file, and load it into Pydantic (v2.11.4).
Here’s what our model looks like:

from pydantic import BaseModel, RootModel

class Name(BaseModel):
 
 

 
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