Add ConfigDict.ser_json_inf_nan (#8159)

Co-authored-by: Sydney Runkle <54324534+sydney-runkle@users.noreply.github.com>
Co-authored-by: Egil-nov <95861118+Egil-nov@users.noreply.github.com>

docs/concepts/json_schema.md

@@ -187,6 +187,7 @@ Specifically, the following config options are relevant:
 * [`json_schema_extra`][pydantic.config.ConfigDict.json_schema_extra]
 * [`ser_json_timedelta`][pydantic.config.ConfigDict.ser_json_timedelta]
 * [`ser_json_bytes`][pydantic.config.ConfigDict.ser_json_bytes]
+* [`ser_json_inf_nan`][pydantic.config.ConfigDict.ser_json_inf_nan]
 
 ### Unenforced `Field` constraints
 

pydantic/_internal/_config.py

@@ -67,6 +67,7 @@ class ConfigWrapper:
     revalidate_instances: Literal['always', 'never', 'subclass-instances']
     ser_json_timedelta: Literal['iso8601', 'float']
     ser_json_bytes: Literal['utf8', 'base64']
+    ser_json_inf_nan: Literal['null', 'constants']
     # whether to validate default values during validation, default False
     validate_default: bool
     validate_return: bool
@@ -167,6 +168,7 @@ def dict_not_none(**kwargs: Any) -> Any:
                 strict=self.config_dict.get('strict'),
                 ser_json_timedelta=self.config_dict.get('ser_json_timedelta'),
                 ser_json_bytes=self.config_dict.get('ser_json_bytes'),
+                ser_json_inf_nan=self.config_dict.get('ser_json_inf_nan'),
                 from_attributes=self.config_dict.get('from_attributes'),
                 loc_by_alias=self.config_dict.get('loc_by_alias'),
                 revalidate_instances=self.config_dict.get('revalidate_instances'),
@@ -236,6 +238,7 @@ def push(self, config_wrapper: ConfigWrapper | ConfigDict | None):
     revalidate_instances='never',
     ser_json_timedelta='iso8601',
     ser_json_bytes='utf8',
+    ser_json_inf_nan='null',
     validate_default=False,
     validate_return=False,
     protected_namespaces=('model_',),

pydantic/config.py

@@ -540,6 +540,15 @@ class Transaction(BaseModel):
     - `'base64'` will serialize bytes to URL safe base64 strings.
     """
 
+    ser_json_inf_nan: Literal['null', 'constants']
+    """
+    The encoding of JSON serialized infinity and NaN float values. Accepts the string values of `'null'` and `'constants'`.
+    Defaults to `'null'`.
+
+    - `'null'` will serialize infinity and NaN values as `null`.
+    - `'constants'` will serialize infinity and NaN values as `Infinity` and `NaN`.
+    """
+
     # whether to validate default values during validation, default False
     validate_default: bool
     """Whether to validate default values during validation. Defaults to `False`."""

tests/test_types.py

@@ -38,7 +38,7 @@
 import annotated_types
 import dirty_equals
 import pytest
-from dirty_equals import HasRepr, IsOneOf, IsStr
+from dirty_equals import HasRepr, IsFloatNan, IsOneOf, IsStr
 from pydantic_core import CoreSchema, PydanticCustomError, SchemaError, core_schema
 from typing_extensions import Annotated, Literal, TypedDict, get_args
 
@@ -2529,7 +2529,7 @@ class Model(BaseModel):
     ]
 
 
-def test_finite_float_validation():
+def test_infinite_float_validation():
     class Model(BaseModel):
         a: float = None
 
@@ -2538,6 +2538,27 @@ class Model(BaseModel):
     assert math.isnan(Model(a=float('nan')).a)
 
 
+@pytest.mark.parametrize(
+    ('ser_json_inf_nan', 'input', 'output', 'python_roundtrip'),
+    (
+        ('null', float('inf'), 'null', None),
+        ('null', float('-inf'), 'null', None),
+        ('null', float('nan'), 'null', None),
+        ('constants', float('inf'), 'Infinity', float('inf')),
+        ('constants', float('-inf'), '-Infinity', float('-inf')),
+        ('constants', float('nan'), 'NaN', IsFloatNan),
+    ),
+)
+def test_infinite_float_json_serialization(ser_json_inf_nan, input, output, python_roundtrip):
+    class Model(BaseModel):
+        model_config = ConfigDict(ser_json_inf_nan=ser_json_inf_nan)
+        a: float
+
+    json_string = Model(a=input).model_dump_json()
+    assert json_string == f'{{"a":{output}}}'
+    assert json.loads(json_string) == {'a': python_roundtrip}
+
+
 @pytest.mark.parametrize('value', [float('inf'), float('-inf'), float('nan')])
 def test_finite_float_validation_error(value):
     class Model(BaseModel):