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# Pydantic Validation
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[Pydantic v2]
[![llms.txt]](https://docs.pydantic.dev/latest/llms.txt)
Data validation using Python type hints.
Fast and extensible, Pydantic plays nicely with your linters/IDE/brain.
Define how data should be in pure, canonical Python 3.9+; validate it with
Pydantic.
## Pydantic Logfire :fire:
We've launched Pydantic Logfire to help you monitor your applications.
[Learn more]
## Pydantic V1.10 vs. V2
Pydantic V2 is a ground-up rewrite that offers many new features,
performance improvements, and some breaking changes compared to Pydantic
V1.
If you're using Pydantic V1 you may want to look at the
[pydantic V1.10 Documentation] or,
[`1.10.X-fixes` git branch]. Pydantic V2 also ships with the latest version
of Pydantic V1 built in so that you can incrementally upgrade your code
base and projects: `from pydantic import v1 as pydantic_v1`.
## Help
See [documentation] for more details.
## Installation
Install using `pip install -U pydantic` or `conda install pydantic -c
conda-forge`.
For more installation options to make Pydantic even faster,
see the [Install] section in the documentation.
## A Simple Example
```python
from datetime import datetime
from typing import Optional
from pydantic import BaseModel
class User(BaseModel):
id: int
name: str = 'John Doe'
signup_ts: Optional[datetime] = None
friends: list[int] = []
external_data = {'id': '123', 'signup_ts': '2017-06-01 12:22', 'friends':
[1, '2', b'3']}
user = User(**external_data)
print(user)
#> User id=123 name='John Doe' signup_ts=datetime.datetime(2017, 6, 1, 12,
22) friends=[1, 2, 3]
print(user.id)
#> 123
```
## Contributing
For guidance on setting up a development environment and how to make a
contribution to Pydantic, see
[Contributing to Pydantic].
## Reporting a Security Vulnerability
See our [security policy].
## Changelog
## v2.13.5 (2026-08-28)
[GitHub release]
### What's Changed
#### Fixes
* Allow reuse of validators when plugins are set by [@Viicos] in [#13535]
* Fix missing GC traversal on some `pydantic-core` struct fields by
[@Viicos] in [#13624]
* Fix missing GC traversal in `pydantic-core` for `GeneralFieldsSerializer`
by [@Viicos] in [#13629]
* Count validated model fields once in smart unions by [@tamird] in
[#13731]
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