BUG: is_datetime64tz_dtype shortcut only for DatetimeTZDtype

doc/source/whatsnew/v1.6.0.rst

@@ -150,6 +150,7 @@ Conversion
 ^^^^^^^^^^
 - Bug in constructing :class:`Series` with ``int64`` dtype from a string list raising instead of casting (:issue:`44923`)
 - Bug in :meth:`DataFrame.eval` incorrectly raising an ``AttributeError`` when there are negative values in function call (:issue:`46471`)
+- Bug where any :class:`ExtensionDtype` subclass with ``kind="M"`` would be interpreted as a timezone type (:issue:`34986`)
 -
 
 Strings

pandas/core/dtypes/common.py

@@ -382,9 +382,10 @@ def is_datetime64tz_dtype(arr_or_dtype) -> bool:
     >>> is_datetime64tz_dtype(s)
     True
     """
-    if isinstance(arr_or_dtype, ExtensionDtype):
+    if isinstance(arr_or_dtype, DatetimeTZDtype):
         # GH#33400 fastpath for dtype object
-        return arr_or_dtype.kind == "M"
+        # GH 34986
+        return True
 
     if arr_or_dtype is None:
         return False

pandas/tests/dtypes/test_common.py

@@ -13,6 +13,7 @@
     CategoricalDtype,
     CategoricalDtypeType,
     DatetimeTZDtype,
+    ExtensionDtype,
     IntervalDtype,
     PeriodDtype,
 )
@@ -239,6 +240,18 @@ def test_is_datetime64tz_dtype():
     assert com.is_datetime64tz_dtype(pd.DatetimeIndex(["2000"], tz="US/Eastern"))
 
 
+def test_custom_ea_kind_M_not_datetime64tz():
+    # GH 34986
+    class NotTZDtype(ExtensionDtype):
+        @property
+        def kind(self) -> str:
+            return "M"
+
+    not_tz_dtype = NotTZDtype()
+    assert not com.is_datetime64tz_dtype(not_tz_dtype)
+    assert not com.needs_i8_conversion(not_tz_dtype)
+
+
 def test_is_timedelta64_dtype():
     assert not com.is_timedelta64_dtype(object)
     assert not com.is_timedelta64_dtype(None)