PYTHON-3062 Make Regex generic (#860)

bson/regex.py

@@ -16,7 +16,7 @@
 """
 
 import re
-from typing import Any, Pattern, Type, Union
+from typing import Any, Generic, Pattern, Type, TypeVar, Union
 
 from bson._helpers import _getstate_slots, _setstate_slots
 from bson.son import RE_TYPE
@@ -40,7 +40,10 @@ def str_flags_to_int(str_flags: str) -> int:
     return flags
 
 
-class Regex(object):
+_T = TypeVar("_T", str, bytes)
+
+
+class Regex(Generic[_T]):
     """BSON regular expression data."""
 
     __slots__ = ("pattern", "flags")
@@ -51,7 +54,7 @@ class Regex(object):
     _type_marker = 11
 
     @classmethod
-    def from_native(cls: Type["Regex"], regex: Pattern[Any]) -> "Regex":
+    def from_native(cls: Type["Regex"], regex: "Pattern[_T]") -> "Regex[_T]":
         """Convert a Python regular expression into a ``Regex`` instance.
 
         Note that in Python 3, a regular expression compiled from a
@@ -80,7 +83,7 @@ class Regex(object):
 
         return Regex(regex.pattern, regex.flags)
 
-    def __init__(self, pattern: Union[str, bytes], flags: Union[str, int] = 0) -> None:
+    def __init__(self, pattern: _T, flags: Union[str, int] = 0) -> None:
         """BSON regular expression data.
 
         This class is useful to store and retrieve regular expressions that are
@@ -93,7 +96,7 @@ class Regex(object):
         """
         if not isinstance(pattern, (str, bytes)):
             raise TypeError("pattern must be a string, not %s" % type(pattern))
-        self.pattern = pattern
+        self.pattern: _T = pattern
 
         if isinstance(flags, str):
             self.flags = str_flags_to_int(flags)
@@ -116,7 +119,7 @@ class Regex(object):
     def __repr__(self):
         return "Regex(%r, %r)" % (self.pattern, self.flags)
 
-    def try_compile(self) -> Pattern[Any]:
+    def try_compile(self) -> "Pattern[_T]":
         """Compile this :class:`Regex` as a Python regular expression.
 
         .. warning::