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pydantic/docs/usage/mypy.md
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Arseny Boykov c24d33e5f1 Generate docs exampels for Python 3.10 and above (#4339)
* Generate docs exampels for Python 3.10 and above

Code quality is not great and main intent here is to show the result.

* Fix docs build on 3.9

* Build docs on 3.10

* What's Python 3.1?

* Create temp dir if not exists

* Refactor and improve imlementetion

* Keep runtime typing in examples

* Revert unrelated formatting changes

* Add changes file

* Allow specifying requirements in examples

* Pin autoflake and pyupgrade

* Add docs/build to Makefile lint/format/mypy

* ignore_missing_imports for ansi2html and devtools

* Add .tmp-projections to .gitignore

* Remove dont-upgrade now when Pattern is supported

* Update postponed evaluation examples

Co-authored-by: Samuel Colvin <s@muelcolvin.com>
2022-08-14 17:21:53 +01:00

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*pydantic* models work with [mypy](http://mypy-lang.org/) provided you use the annotation-only version of
required fields:
{!.tmp_examples/mypy_main.md!}
You can run your code through mypy with:
```bash
mypy \
--ignore-missing-imports \
--follow-imports=skip \
--strict-optional \
pydantic_mypy_test.py
```
If you call mypy on the example code above, you should see mypy detect the attribute access error:
```
13: error: "Model" has no attribute "middle_name"
```
## Strict Optional
For your code to pass with `--strict-optional`, you need to to use `Optional[]` or an alias of `Optional[]`
for all fields with `None` as the default. (This is standard with mypy.)
Pydantic provides a few useful optional or union types:
* `NoneStr` aka. `Optional[str]`
* `NoneBytes` aka. `Optional[bytes]`
* `StrBytes` aka. `Union[str, bytes]`
* `NoneStrBytes` aka. `Optional[StrBytes]`
If these aren't sufficient you can of course define your own.
## Mypy Plugin
Pydantic ships with a mypy plugin that adds a number of important pydantic-specific
features to mypy that improve its ability to type-check your code.
See the [pydantic mypy plugin docs](../mypy_plugin.md) for more details.
## Other pydantic interfaces
Pydantic [dataclasses](dataclasses.md) and the [`validate_arguments` decorator](validation_decorator.md)
should also work well with mypy.