Add support for re.Pattern (#4366)

changes/4366-hramezani.md

@@ -0,0 +1 @@
+Add support for `re.Pattern`

pydantic/fields.py

@@ -1,4 +1,5 @@
 import copy
+import re
 from collections import Counter as CollectionCounter, defaultdict, deque
 from collections.abc import Callable, Hashable as CollectionsHashable, Iterable as CollectionsIterable
 from typing import (
@@ -595,7 +596,7 @@ def _type_analysis(self) -> None:  # noqa: C901 (ignore complexity)
                 self.required = False
             self.allow_none = True
             return
-        elif self.type_ is Pattern:
+        elif self.type_ is Pattern or self.type_ is re.Pattern:
             # python 3.7 only, Pattern is a typing object but without sub fields
             return
         elif is_literal_type(self.type_):

pydantic/schema.py

@@ -803,7 +803,7 @@ def add_field_type_to_schema(field_type: Any, schema_: Dict[str, Any]) -> None:
     and then modifies the given `schema` with the information from that type.
     """
     for type_, t_schema in field_class_to_schema:
-        # Fallback for `typing.Pattern` as it is not a valid class
+        # Fallback for `typing.Pattern` and `re.Pattern` as they are not a valid class
         if lenient_issubclass(field_type, type_) or field_type is type_ is Pattern:
             schema_.update(t_schema)
             break

pydantic/validators.py

@@ -684,7 +684,7 @@ def find_validators(  # noqa: C901 (ignore complexity)
     if is_none_type(type_):
         yield none_validator
         return
-    if type_ is Pattern:
+    if type_ is Pattern or type_ is re.Pattern:
         yield pattern_validator
         return
     if type_ is Hashable or type_ is CollectionsHashable:

tests/test_types.py

@@ -2540,9 +2540,10 @@ class JsonRequired(BaseModel):
     assert JsonRequired().dict() == {'json_obj': None}
 
 
-def test_pattern():
+@pytest.mark.parametrize('pattern_type', [re.Pattern, Pattern])
+def test_pattern(pattern_type):
     class Foobar(BaseModel):
-        pattern: Pattern
+        pattern: pattern_type
 
     f = Foobar(pattern=r'^whatev.r\d$')
     assert f.pattern.__class__.__name__ == 'Pattern'
@@ -2563,9 +2564,10 @@ class Foobar(BaseModel):
     }
 
 
-def test_pattern_error():
+@pytest.mark.parametrize('pattern_type', [re.Pattern, Pattern])
+def test_pattern_error(pattern_type):
     class Foobar(BaseModel):
-        pattern: Pattern
+        pattern: pattern_type
 
     with pytest.raises(ValidationError) as exc_info:
         Foobar(pattern='[xx')