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