Add support for field level number to str coercion option (#9137)

Co-authored-by: Sydney Runkle <54324534+sydney-runkle@users.noreply.github.com>
Co-authored-by: sydney-runkle <sydneymarierunkle@gmail.com>

pydantic/_internal/_known_annotated_metadata.py

@@ -19,7 +19,15 @@
 INEQUALITY = {'le', 'ge', 'lt', 'gt'}
 NUMERIC_CONSTRAINTS = {'multiple_of', 'allow_inf_nan', *INEQUALITY}
 
-STR_CONSTRAINTS = {*SEQUENCE_CONSTRAINTS, *STRICT, 'strip_whitespace', 'to_lower', 'to_upper', 'pattern'}
+STR_CONSTRAINTS = {
+    *SEQUENCE_CONSTRAINTS,
+    *STRICT,
+    'strip_whitespace',
+    'to_lower',
+    'to_upper',
+    'pattern',
+    'coerce_numbers_to_str',
+}
 BYTES_CONSTRAINTS = {*SEQUENCE_CONSTRAINTS, *STRICT}
 
 LIST_CONSTRAINTS = {*SEQUENCE_CONSTRAINTS, *STRICT}
@@ -279,6 +287,13 @@ def apply_known_metadata(annotation: Any, schema: CoreSchema) -> CoreSchema | No
                 partial(_validators.max_length_validator, max_length=annotation.max_length),
                 schema,
             )
+        elif constraint == 'coerce_numbers_to_str':
+            return cs.chain_schema(
+                [
+                    schema,
+                    cs.str_schema(coerce_numbers_to_str=True),  # type: ignore
+                ]
+            )
         else:
             raise RuntimeError(f'Unable to apply constraint {constraint} to schema {schema_type}')
 

pydantic/fields.py

@@ -78,6 +78,7 @@ class _FromFieldInfoInputs(typing_extensions.TypedDict, total=False):
     init: bool | None
     init_var: bool | None
     kw_only: bool | None
+    coerce_numbers_to_str: bool | None
 
 
 class _FieldInfoInputs(_FromFieldInfoInputs, total=False):
@@ -184,6 +185,7 @@ class FieldInfo(_repr.Representation):
         'max_digits': None,
         'decimal_places': None,
         'union_mode': None,
+        'coerce_numbers_to_str': None,
     }
 
     def __init__(self, **kwargs: Unpack[_FieldInfoInputs]) -> None:
@@ -656,6 +658,7 @@ class _EmptyKwargs(typing_extensions.TypedDict):
     decimal_places=None,
     min_length=None,
     max_length=None,
+    coerce_numbers_to_str=None,
 )
 
 
@@ -682,6 +685,7 @@ def Field(  # noqa: C901
     kw_only: bool | None = _Unset,
     pattern: str | typing.Pattern[str] | None = _Unset,
     strict: bool | None = _Unset,
+    coerce_numbers_to_str: bool | None = _Unset,
     gt: float | None = _Unset,
     ge: float | None = _Unset,
     lt: float | None = _Unset,
@@ -731,6 +735,7 @@ def Field(  # noqa: C901
             (Only applies to dataclasses.)
         kw_only: Whether the field should be a keyword-only argument in the constructor of the dataclass.
             (Only applies to dataclasses.)
+        coerce_numbers_to_str: Whether to enable coercion of any `Number` type to `str` (not applicable in `strict` mode).
         strict: If `True`, strict validation is applied to the field.
             See [Strict Mode](../concepts/strict_mode.md) for details.
         gt: Greater than. If set, value must be greater than this. Only applicable to numbers.
@@ -843,6 +848,7 @@ def Field(  # noqa: C901
         init=init,
         init_var=init_var,
         kw_only=kw_only,
+        coerce_numbers_to_str=coerce_numbers_to_str,
         strict=strict,
         gt=gt,
         ge=ge,

tests/test_fields.py

@@ -144,3 +144,29 @@ def prop_field(self):
 
     with pytest.raises(AttributeError, match=f"'{Model.__name__}' object has no attribute 'invalid_field'"):
         Model().invalid_field
+
+
+@pytest.mark.parametrize('number', (1, 42, 443, 11.11, 0.553))
+def test_coerce_numbers_to_str_field_option(number):
+    class Model(BaseModel):
+        field: str = Field(coerce_numbers_to_str=True, max_length=10)
+
+    assert Model(field=number).field == str(number)
+
+
+@pytest.mark.parametrize('number', (1, 42, 443, 11.11, 0.553))
+def test_coerce_numbers_to_str_field_precedence(number):
+    class Model(BaseModel):
+        model_config = ConfigDict(coerce_numbers_to_str=True)
+
+        field: str = Field(coerce_numbers_to_str=False)
+
+    with pytest.raises(ValidationError):
+        Model(field=number)
+
+    class Model(BaseModel):
+        model_config = ConfigDict(coerce_numbers_to_str=False)
+
+        field: str = Field(coerce_numbers_to_str=True)
+
+    assert Model(field=number).field == str(number)