Use abc.ABC as baseclass for AnyPath to fix issubclass behavior (#251)

* Use abc.ABC as baseclass for AnyPath

* add type ignore for ABC.register

cloudpathlib/anypath.py

@@ -1,24 +1,13 @@
 import os
+from abc import ABC
 from pathlib import Path
 from typing import Union
 
 from .cloudpath import InvalidPrefixError, CloudPath
 from .exceptions import AnyPathTypeError
 
 
-class AnyPathMeta(type):
-    """Metaclass for AnyPath that implements special methods so that AnyPath works as a virtual
-    superclass when using isinstance or issubclass checks on CloudPath or Path inputs. See
-    [PEP 3119](https://www.python.org/dev/peps/pep-3119/#overloading-isinstance-and-issubclass)."""
-
-    def __instancecheck__(cls, inst):
-        return isinstance(inst, CloudPath) or isinstance(inst, Path)
-
-    def __subclasscheck__(cls, sub):
-        return issubclass(sub, CloudPath) or issubclass(sub, Path)
-
-
-class AnyPath(metaclass=AnyPathMeta):
+class AnyPath(ABC):
     """Polymorphic virtual superclass for CloudPath and pathlib.Path. Constructing an instance will
     automatically dispatch to CloudPath or Path based on the input. It also supports both
     isinstance and issubclass checks.
@@ -55,6 +44,10 @@ def _validate(cls, value) -> Union[CloudPath, Path]:
         return cls.__new__(cls, value)
 
 
+AnyPath.register(CloudPath)  # type: ignore
+AnyPath.register(Path)
+
+
 def to_anypath(s: Union[str, os.PathLike]) -> Union[CloudPath, Path]:
     """Convenience method to convert a str or os.PathLike to the
     proper Path or CloudPath object using AnyPath.

tests/test_anypath.py

@@ -36,3 +36,7 @@ def test_anypath_cloudpath(rig):
 def test_anypath_bad_input():
     with pytest.raises(AnyPathTypeError):
         AnyPath(0)
+
+
+def test_anypath_subclass_anypath():
+    assert issubclass(AnyPath, AnyPath)