mirror of
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Arseny Boykov
c24d33e5f1
* 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>
50 lines
2.0 KiB
Markdown
50 lines
2.0 KiB
Markdown
!!! note
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Both postponed annotations via the future import and `ForwardRef` require Python 3.7+.
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Postponed annotations (as described in [PEP563](https://www.python.org/dev/peps/pep-0563/))
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"just work".
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{!.tmp_examples/postponed_annotations_main.md!}
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Internally, *pydantic* will call a method similar to `typing.get_type_hints` to resolve annotations.
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In cases where the referenced type is not yet defined, `ForwardRef` can be used (although referencing the
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type directly or by its string is a simpler solution in the case of
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[self-referencing models](#self-referencing-models)).
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In some cases, a `ForwardRef` won't be able to be resolved during model creation.
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For example, this happens whenever a model references itself as a field type.
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When this happens, you'll need to call `update_forward_refs` after the model has been created before it can be used:
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{!.tmp_examples/postponed_annotations_forward_ref.md!}
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!!! warning
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To resolve strings (type names) into annotations (types), *pydantic* needs a namespace dict in which to
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perform the lookup. For this it uses `module.__dict__`, just like `get_type_hints`.
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This means *pydantic* may not play well with types not defined in the global scope of a module.
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For example, this works fine:
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{!.tmp_examples/postponed_annotations_works.md!}
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While this will break:
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{!.tmp_examples/postponed_annotations_broken.md!}
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Resolving this is beyond the call for *pydantic*: either remove the future import or declare the types globally.
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## Self-referencing Models
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Data structures with self-referencing models are also supported. Self-referencing fields will be automatically
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resolved after model creation.
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Within the model, you can refer to the not-yet-constructed model using a string:
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{!.tmp_examples/postponed_annotations_self_referencing_string.md!}
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Since Python 3.7, you can also refer it by its type, provided you import `annotations` (see
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[above](postponed_annotations.md) for support depending on Python
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and *pydantic* versions).
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{!.tmp_examples/postponed_annotations_self_referencing_annotations.md!}
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