ENH: DatetimeTZDtype support non-nano (pandas-dev#47120)

* ENH: DatetimeTZDtype support non-nano

* mypy fixup

* mypy fixup

* TST: Day not supported

pandas/_libs/tslibs/dtypes.pyi

@@ -56,3 +56,19 @@ class Resolution(Enum):
     def get_reso_from_freqstr(cls, freq: str) -> Resolution: ...
     @property
     def attr_abbrev(self) -> str: ...
+
+class NpyDatetimeUnit(Enum):
+    NPY_FR_Y: int
+    NPY_FR_M: int
+    NPY_FR_W: int
+    NPY_FR_D: int
+    NPY_FR_h: int
+    NPY_FR_m: int
+    NPY_FR_s: int
+    NPY_FR_ms: int
+    NPY_FR_us: int
+    NPY_FR_ns: int
+    NPY_FR_ps: int
+    NPY_FR_fs: int
+    NPY_FR_as: int
+    NPY_FR_GENERIC: int

pandas/_libs/tslibs/dtypes.pyx

@@ -257,6 +257,26 @@ class Resolution(Enum):
         return cls.from_attrname(attr_name)
 
 
+class NpyDatetimeUnit(Enum):
+    """
+    Python-space analogue to NPY_DATETIMEUNIT.
+    """
+    NPY_FR_Y = NPY_DATETIMEUNIT.NPY_FR_Y
+    NPY_FR_M = NPY_DATETIMEUNIT.NPY_FR_M
+    NPY_FR_W = NPY_DATETIMEUNIT.NPY_FR_W
+    NPY_FR_D = NPY_DATETIMEUNIT.NPY_FR_D
+    NPY_FR_h = NPY_DATETIMEUNIT.NPY_FR_h
+    NPY_FR_m = NPY_DATETIMEUNIT.NPY_FR_m
+    NPY_FR_s = NPY_DATETIMEUNIT.NPY_FR_s
+    NPY_FR_ms = NPY_DATETIMEUNIT.NPY_FR_ms
+    NPY_FR_us = NPY_DATETIMEUNIT.NPY_FR_us
+    NPY_FR_ns = NPY_DATETIMEUNIT.NPY_FR_ns
+    NPY_FR_ps = NPY_DATETIMEUNIT.NPY_FR_ps
+    NPY_FR_fs = NPY_DATETIMEUNIT.NPY_FR_fs
+    NPY_FR_as = NPY_DATETIMEUNIT.NPY_FR_as
+    NPY_FR_GENERIC = NPY_DATETIMEUNIT.NPY_FR_GENERIC
+
+
 cdef str npy_unit_to_abbrev(NPY_DATETIMEUNIT unit):
     if unit == NPY_DATETIMEUNIT.NPY_FR_ns or unit == NPY_DATETIMEUNIT.NPY_FR_GENERIC:
         # generic -> default to nanoseconds

pandas/core/dtypes/dtypes.py

@@ -670,14 +670,17 @@ class DatetimeTZDtype(PandasExtensionDtype):
 
     type: type[Timestamp] = Timestamp
     kind: str_type = "M"
-    str = "|M8[ns]"
     num = 101
-    base = np.dtype("M8[ns]")
+    base = np.dtype("M8[ns]")  # TODO: depend on reso?
     na_value = NaT
     _metadata = ("unit", "tz")
     _match = re.compile(r"(datetime64|M8)\[(?P<unit>.+), (?P<tz>.+)\]")
     _cache_dtypes: dict[str_type, PandasExtensionDtype] = {}
 
+    @cache_readonly
+    def str(self):
+        return f"|M8[{self._unit}]"
+
     def __init__(self, unit: str_type | DatetimeTZDtype = "ns", tz=None) -> None:
         if isinstance(unit, DatetimeTZDtype):
             # error: "str" has no attribute "tz"
@@ -696,8 +699,8 @@ def __init__(self, unit: str_type | DatetimeTZDtype = "ns", tz=None) -> None:
                     "'DatetimeTZDtype.construct_from_string()' instead."
                 )
                 raise ValueError(msg)
-            else:
-                raise ValueError("DatetimeTZDtype only supports ns units")
+            if unit not in ["s", "ms", "us", "ns"]:
+                raise ValueError("DatetimeTZDtype only supports s, ms, us, ns units")
 
         if tz:
             tz = timezones.maybe_get_tz(tz)
@@ -710,6 +713,19 @@ def __init__(self, unit: str_type | DatetimeTZDtype = "ns", tz=None) -> None:
         self._unit = unit
         self._tz = tz
 
+    @cache_readonly
+    def _reso(self) -> int:
+        """
+        The NPY_DATETIMEUNIT corresponding to this dtype's resolution.
+        """
+        reso = {
+            "s": dtypes.NpyDatetimeUnit.NPY_FR_s,
+            "ms": dtypes.NpyDatetimeUnit.NPY_FR_ms,
+            "us": dtypes.NpyDatetimeUnit.NPY_FR_us,
+            "ns": dtypes.NpyDatetimeUnit.NPY_FR_ns,
+        }[self._unit]
+        return reso.value
+
     @property
     def unit(self) -> str_type:
         """

pandas/tests/dtypes/test_dtypes.py

@@ -4,6 +4,8 @@
 import pytest
 import pytz
 
+from pandas._libs.tslibs.dtypes import NpyDatetimeUnit
+
 from pandas.core.dtypes.base import _registry as registry
 from pandas.core.dtypes.common import (
     is_bool_dtype,
@@ -263,10 +265,17 @@ def test_hash_vs_equality(self, dtype):
         assert dtype2 != dtype4
         assert hash(dtype2) != hash(dtype4)
 
-    def test_construction(self):
-        msg = "DatetimeTZDtype only supports ns units"
+    def test_construction_non_nanosecond(self):
+        res = DatetimeTZDtype("ms", "US/Eastern")
+        assert res.unit == "ms"
+        assert res._reso == NpyDatetimeUnit.NPY_FR_ms.value
+        assert res.str == "|M8[ms]"
+        assert str(res) == "datetime64[ms, US/Eastern]"
+
+    def test_day_not_supported(self):
+        msg = "DatetimeTZDtype only supports s, ms, us, ns units"
         with pytest.raises(ValueError, match=msg):
-            DatetimeTZDtype("ms", "US/Eastern")
+            DatetimeTZDtype("D", "US/Eastern")
 
     def test_subclass(self):
         a = DatetimeTZDtype.construct_from_string("datetime64[ns, US/Eastern]")