---
id: lazy-model
version: "0.4.0"
license: Apache-2.0
license_treatment: permissive
maintenance: aging
---

# lazy-model

License: permissive · Maintenance: aging · Downloads: 1.7M/mo

## What it is and what it does

Lazy-model wraps Pydantic models to defer field parsing until access time. Instead of validating and converting all fields when an object is created, it stores raw input data and only processes each field when you read it. This can reduce startup latency for objects with many fields or expensive validators that you may never use.

The library integrates directly with Pydantic's validator system, so custom validators run during lazy parsing just as they would in a standard Pydantic model. Fields are marked as unparsed (NAO—Not An Object) until accessed, at which point type conversion and validation occur. It depends only on pydantic and supports Python 3.9 and later.

Use it for:

- Parse large API responses where only a subset of fields are typically accessed in a given request.
- Reduce initialization time for objects with many fields or computationally expensive validators.
- Build data pipelines where partial object inspection happens before full validation is needed.
- Defer validation errors until the specific field is actually used, improving error locality.
- Handle deeply nested structures where intermediate layers may not need immediate parsing.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Lazy-model provides on-demand field parsing for Pydantic models, deferring validation and type conversion until each field is actually accessed rather than parsing the entire object upfront.

Yes, if you work with Pydantic models and have a specific use case for deferred parsing (large objects, expensive validators, or partial field access patterns). The low install friction and permissive license make it a low-risk experiment. However, verify compatibility with your Pydantic version and measure whether lazy parsing actually improves your workload, since the aging maintenance status suggests limited ongoing development.

## Install

pip install lazy-model
uv add lazy-model
poetry add lazy-model

## Installing lazy-model

Before you install: Low friction: pure Python wheel with a single runtime dependency on pydantic. Maintenance signal is aging—no release activity for 372 days, though the latest release is recent (2025-08-07), suggesting the project may be stable rather than abandoned.

License in practice: Apache-2.0 is permissive; you can use, modify, and distribute this package freely in commercial and private projects with minimal restrictions.

Quickstart:

from lazy_model import LazyModel
from pydantic import validator

class Sample(LazyModel):
    i: int
    s: str

obj = Sample.lazy_parse({"i": "10", "s": "test"})
print(obj.i)  # Parses and converts on first access

Requires Python 3.9 or later; pydantic must be installed as a runtime dependency.

Verify before relying:

- Performance impact of lazy parsing vs. eager parsing in typical workloads remains unquantified.
- Compatibility with Pydantic v2 and its breaking changes from v1 is unclear from the fact sheet.

## Package facts

- License: Apache-2.0 (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: aging
- Downloads: 1.7M/month (top 5,000 on PyPI)
- Known vulnerabilities: none known

## Tags

lazy parsing pydantic, deferred field validation, on-demand object parsing, lazy model loading, pydantic lazy evaluation, defer validation until access, lazy deserialization, pydantic-extension, lazy-evaluation

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