DEPR: emit a FutureWarning when mutating Time.location post-initialization

astropy/io/fits/tests/test_fitstime.py

@@ -42,11 +42,14 @@ def test_time_to_fits_loc(self, table_types):
         columns in a ``Table``.
         """
         t = table_types()
-        t["a"] = Time(self.time, format="isot", scale="utc")
-        t["b"] = Time(self.time, format="isot", scale="tt")
-
         # Check that vectorized location is stored using Green Bank convention
-        t["a"].location = EarthLocation([1.0, 2.0], [2.0, 3.0], [3.0, 4.0], unit="Mm")
+        t["a"] = Time(
+            self.time,
+            format="isot",
+            scale="utc",
+            location=EarthLocation([1.0, 2.0], [2.0, 3.0], [3.0, 4.0], unit="Mm"),
+        )
+        t["b"] = Time(self.time, format="isot", scale="tt")
 
         with pytest.warns(
             AstropyUserWarning,
@@ -83,15 +86,19 @@ def test_time_to_fits_loc(self, table_types):
         assert tm["b"].location == t["b"].location
 
         # Check that multiple Time columns with different locations raise an exception
-        t["a"].location = EarthLocation(1, 2, 3)
-        t["b"].location = EarthLocation(2, 3, 4)
+        t["a"] = Time(
+            self.time, format="isot", scale="utc", location=EarthLocation(1, 2, 3)
+        )
+        t["b"] = Time(
+            self.time, format="isot", scale="tt", location=EarthLocation(2, 3, 4)
+        )
 
         with pytest.raises(ValueError) as err:
             table, hdr = time_to_fits(t)
             assert "Multiple Time Columns with different geocentric" in str(err.value)
 
         # Check that Time column with no location specified will assume global location
-        t["b"].location = None
+        t["b"] = Time(self.time, format="isot", scale="tt", location=None)
 
         with pytest.warns(
             AstropyUserWarning,
@@ -104,7 +111,9 @@ def test_time_to_fits_loc(self, table_types):
         assert len(w) == 1
 
         # Check that multiple Time columns with same location can be written
-        t["b"].location = EarthLocation(1, 2, 3)
+        t["b"] = Time(
+            self.time, format="isot", scale="tt", location=EarthLocation(1, 2, 3)
+        )
 
         table, hdr = time_to_fits(t)
 

astropy/time/core.py

@@ -5,6 +5,7 @@
 UT1) and time representations (e.g. JD, MJD, ISO 8601) that are used in
 astronomy.
 """
+from __future__ import annotations
 
 import copy
 import enum
@@ -14,6 +15,7 @@
 from collections import defaultdict
 from datetime import date, datetime, timezone
 from time import strftime
+from typing import TYPE_CHECKING
 from warnings import warn
 from weakref import WeakValueDictionary
 
@@ -46,6 +48,8 @@
 from .time_helper.function_helpers import CUSTOM_FUNCTIONS, UNSUPPORTED_FUNCTIONS
 from .utils import day_frac
 
+if TYPE_CHECKING:
+    from astropy.coordinates import EarthLocation
 __all__ = [
     "TimeBase",
     "Time",
@@ -554,7 +558,7 @@
         # collected by the TimeAstropyTime format class up to the Time level.
         # TODO: find a nicer way.
         if hasattr(self._time, "_location"):
-            self.location = self._time._location
+            self._location = self._time._location
             del self._time._location
 
         # If any inputs were masked then masked jd2 accordingly.  From above
@@ -744,6 +748,24 @@
 
             raise TypeError(f"unhashable type: '{self.__class__.__name__}' {reason}")
 
+    @property
+    def location(self) -> EarthLocation | None:
+        return self._location
+
+    @location.setter
+    def location(self, value):
+        if hasattr(self, "_location"):
+            # since astropy 6.1.0
+            warn(
+                "Setting the location attribute post initialization will be "
+                "disallowed in a future version of Astropy. "
+                "Instead you should set the location when creating the Time object. "
+                "In the future, this will raise an AttributeError.",
+                category=FutureWarning,
+                stacklevel=2,
+            )
+        self._location = value
+
     @property
     def scale(self):
         """Time scale."""
@@ -1377,7 +1399,7 @@
         )
 
         # Optional ndarray attributes.
-        for attr in ("_delta_ut1_utc", "_delta_tdb_tt", "location"):
+        for attr in ("_delta_ut1_utc", "_delta_tdb_tt", "_location"):
             try:
                 val = getattr(self, attr)
             except AttributeError:
@@ -1953,14 +1975,13 @@
             from astropy.coordinates import EarthLocation
 
             if isinstance(location, EarthLocation):
-                self.location = location
+                self._location = location
             else:
-                self.location = EarthLocation(*location)
-            if self.location.size == 1:
-                self.location = self.location.squeeze()
-        else:
-            if not hasattr(self, "location"):
-                self.location = None
+                self._location = EarthLocation(*location)
+            if self._location.size == 1:
+                self._location = self._location.squeeze()
+        elif not hasattr(self, "_location"):
+            self._location = None
 
         if isinstance(val, Time):
             # Update _time formatting parameters if explicitly specified
@@ -1984,7 +2005,7 @@
         ):
             try:
                 # check the location can be broadcast to self's shape.
-                self.location = np.broadcast_to(self.location, self.shape, subok=True)
+                self._location = np.broadcast_to(self._location, self.shape, subok=True)
             except Exception as err:
                 raise ValueError(
                     f"The location with shape {self.location.shape} cannot be "
@@ -2777,7 +2798,7 @@
 
                 location = self.location[tuple(sl)]
 
-        result.location = location
+        result._location = location
         return result
 
     def __array_function__(self, function, types, args, kwargs):

astropy/time/tests/test_basic.py

@@ -2883,3 +2883,16 @@ def test_timedelta_empty_quantity():
 
     with pytest.raises(ValueError, match="only quantities with time units"):
         TimeDelta([] * u.m)
+
+
+@pytest.mark.parametrize(
+    "kwargs", [{}, dict(location=None), dict(location=EarthLocation(0, 0, 0))]
+)
+def test_immutable_location(kwargs):
+    # see https://github.com/astropy/astropy/issues/16061
+    loc = EarthLocation(0, 0, 0)
+    t = Time("2024-02-19", **kwargs)
+
+    with pytest.warns(FutureWarning):
+        # in the future, this should be an AttributeError
+        t.location = loc

docs/changes/time/16063.api.rst

@@ -0,0 +1 @@
+A ``FutureWarning`` is now emitted when mutating ``Time.location`` post-initialization.