Add better support for floating point multiple_of values (#652)

- modulo doesn't work with floating point values in many cases, e.g. `0.3 % 0.1 == 0.09999999999999998`
 - port implementation from: https://github.com/tdegrunt/jsonschema/issues/187#issuecomment-320664251
 - add tests for int/float multiple_of values
 - update history with pr/author

HISTORY.rst

@@ -5,6 +5,7 @@ History
 
 v0.31 (unreleased)
 ..................
+* better support for floating point `multiple_of` values, #652 by @justindujardin
 * fix schema generation for ``NewType`` and ``Literal``, #649 by @dmontagu
 * add documentation for Literal type, #651 by @dmontagu
 

pydantic/validators.py

@@ -29,6 +29,7 @@ from .utils import (
     AnyCallable,
     AnyType,
     ForwardRef,
+    almost_equal_floats,
     change_exception,
     display_as_type,
     is_callable_type,
@@ -121,9 +122,10 @@ def float_validator(v: Any) -> float:
 
 def number_multiple_validator(v: 'Number', field: 'Field') -> 'Number':
     field_type: ConstrainedNumber = field.type_  # type: ignore
-    if field_type.multiple_of is not None and v % field_type.multiple_of != 0:  # type: ignore
-        raise errors.NumberNotMultipleError(multiple_of=field_type.multiple_of)
-
+    if field_type.multiple_of is not None:
+        mod = float(v) / float(field_type.multiple_of) % 1
+        if not almost_equal_floats(mod, 0.0) and not almost_equal_floats(mod, 1.0):
+            raise errors.NumberNotMultipleError(multiple_of=field_type.multiple_of)
     return v
 
 

tests/test_types.py

@@ -1422,16 +1422,42 @@ def test_number_le():
         Model(a=6)
 
 
-def test_number_multiple_of():
+@pytest.mark.parametrize('value', ((10), (100), (20)))
+def test_number_multiple_of_int_valid(value):
     class Model(BaseModel):
         a: conint(multiple_of=5)
 
-    assert Model(a=10).dict() == {'a': 10}
+    assert Model(a=value).dict() == {'a': value}
+
+
+@pytest.mark.parametrize('value', ((1337), (23), (6), (14)))
+def test_number_multiple_of_int_invalid(value):
+    class Model(BaseModel):
+        a: conint(multiple_of=5)
 
     multiple_message = base_message.replace('limit_value', 'multiple_of')
     message = multiple_message.format(msg='a multiple of 5', ty='multiple', value=5)
     with pytest.raises(ValidationError, match=message):
-        Model(a=42)
+        Model(a=value)
+
+
+@pytest.mark.parametrize('value', ((0.2), (0.3), (0.4), (0.5), (1)))
+def test_number_multiple_of_float_valid(value):
+    class Model(BaseModel):
+        a: confloat(multiple_of=0.1)
+
+    assert Model(a=value).dict() == {'a': value}
+
+
+@pytest.mark.parametrize('value', ((0.07), (1.27), (1.003)))
+def test_number_multiple_of_float_invalid(value):
+    class Model(BaseModel):
+        a: confloat(multiple_of=0.1)
+
+    multiple_message = base_message.replace('limit_value', 'multiple_of')
+    message = multiple_message.format(msg='a multiple of 0.1', ty='multiple', value=0.1)
+    with pytest.raises(ValidationError, match=message):
+        Model(a=value)
 
 
 @pytest.mark.parametrize('fn', [conint, confloat, condecimal])