Use zoneinfo as single source of truth and tz as interface point

pvlib/location.py

@@ -6,6 +6,7 @@
 
 import pathlib
 import datetime
+import zoneinfo
 
 import pandas as pd
 import pytz
@@ -21,12 +22,15 @@ class Location:
     time zone, and altitude data associated with a particular geographic
     location. You can also assign a name to a location object.
 
-    Location objects have two time-zone attributes, either of which can be
-    individually changed after the Location object has been instantiated and
-    the other will stay in sync:
+    Location objects have two time-zone attributes:
 
-        * ``tz`` is a IANA time-zone string.
-        * ``pytz`` is a pytz time-zone object.
+        * ``tz`` is an IANA time-zone string.
+        * ``pytz`` is a pytz-based time-zone object (read-only).
+        * ``zoneinfo`` is a zoneinfo.ZoneInfo time-zone object (read-only).
+
+    As with Location-object initialization, use the ``tz`` attribute update
+    the Location's time zone after instantiation, and the read-only ``pytz``
+    and ``zoneinfo`` attributes will stay in sync with any change in ``tz``.
 
     Location objects support the print method.
 
@@ -42,14 +46,16 @@ class Location:
 
     tz : time zone as str, int, float, or datetime.tzinfo (inc. subclasses
         from the pytz and zoneinfo packages), default 'UTC'.
-        See http://en.wikipedia.org/wiki/List_of_tz_database_time_zones for a
-        list of valid name strings for IANA time zones.
-        ints and floats must be non-fractional N-hour offsets from UTC, which
-        are converted to the 'Etc/GMT-N' format (note limited range of N and
-        its conventional sign change).
+        This value is stored as a valid IANA time zone name string. See
+        http://en.wikipedia.org/wiki/List_of_tz_database_time_zones for a
+        list of valid name strings, any of which may be passed directly here.
+        ints and floats must be whole-number hour offsets from UTC, which
+        are converted to the IANA-suppored 'Etc/GMT-N' format (note the
+        limited range of the offset N and its sign-change convention).
         Raises TypeError for time zone conversion issues or
-        pytz.exceptions.UnknownTimeZoneError when (stringified) time zone is
-        not recognized by pytz.timezone.
+        zoneinfo.ZoneInfoNotFoundError when the (stringified) time zone is
+        not recognized as an IANA time zone by the zoneinfo.ZoneInfo
+        initializer used for internal time-zone representation.
 
     altitude : float, optional
         Altitude from sea level in meters.
@@ -87,33 +93,41 @@ def __repr__(self):
 
     @property
     def tz(self):
-        # self.pytz holds the single source of time-zone truth.
-        return self.pytz.zone
+        return str(self._zoneinfo)
 
     @tz.setter
     def tz(self, tz_):
+        # self._zoneinfo holds single source of time-zone truth as IANA name.
         if isinstance(tz_, str):
-            self.pytz = pytz.timezone(tz_)
+            self._zoneinfo = zoneinfo.ZoneInfo(tz_)
         elif isinstance(tz_, int):
-            self.pytz = pytz.timezone(f"Etc/GMT{-tz_:+d}")
+            self._zoneinfo = zoneinfo.ZoneInfo(f"Etc/GMT{-tz_:+d}")
         elif isinstance(tz_, float):
             if tz_ % 1 != 0:
                 raise TypeError(
-                    "floating point tz does not have zero fractional part: "
-                    f"{tz_}"
+                    "Floating-point tz has non-zero fractional part: "
+                    f"{tz_}. Only whole-number offsets are supported."
                 )
 
-            self.pytz = pytz.timezone(f"Etc/GMT{-int(tz_):+d}")
+            self._zoneinfo = zoneinfo.ZoneInfo(f"Etc/GMT{-int(tz_):+d}")
         elif isinstance(tz_, datetime.tzinfo):
             # Includes time zones generated by pytz and zoneinfo packages.
-            self.pytz = pytz.timezone(str(tz_))
+            self._zoneinfo = zoneinfo.ZoneInfo(str(tz_))
         else:
             raise TypeError(
                 f"invalid tz specification: {tz_}, must be an IANA time zone "
-                "string, a non-fractional int/float UTC offset, or a "
+                "string, a whole-number int/float UTC offset, or a "
                 "datetime.tzinfo object (including subclasses)"
             )
 
+    @property
+    def pytz(self):
+        return pytz.timezone(str(self._zoneinfo))
+
+    @property
+    def zoneinfo(self):
+        return self._zoneinfo
+
     @classmethod
     def from_tmy(cls, tmy_metadata, tmy_data=None, **kwargs):
         """

pvlib/tests/test_location.py

@@ -10,7 +10,6 @@
 import pytest
 
 import pytz
-from pytz.exceptions import UnknownTimeZoneError
 
 import pvlib
 from pvlib import location
@@ -62,11 +61,6 @@ def test_location_tz_update():
     assert loc.tz == 'Etc/GMT-7'
     assert loc.pytz == pytz.timezone('Etc/GMT-7')
 
-    # Updating pytz updates tz.
-    loc.pytz = pytz.timezone('US/Arizona')
-    assert loc.tz == 'US/Arizona'
-    assert loc.pytz == pytz.timezone('US/Arizona')
-
 
 @pytest.mark.parametrize(
     'tz', [
@@ -76,7 +70,7 @@ def test_location_tz_update():
     ]
 )
 def test_location_invalid_tz(tz):
-    with pytest.raises(UnknownTimeZoneError):
+    with pytest.raises(zoneinfo.ZoneInfoNotFoundError):
         Location(32.2, -111, tz)
 
 

pvlib/tools.py

@@ -3,10 +3,11 @@
 """
 
 import datetime as dt
+import warnings
+
 import numpy as np
 import pandas as pd
 import pytz
-import warnings
 
 
 def cosd(angle):
@@ -125,7 +126,7 @@ def localize_to_utc(time, location):
     ----------
     time : datetime.datetime, pandas.DatetimeIndex,
            or pandas.Series/DataFrame with a DatetimeIndex.
-    location : pvlib.Location object (unused if time is localized)
+    location : pvlib.Location object (unused if ``time`` is localized)
 
     Returns
     -------