BUG: cannot subtract times with different offset (pandas-dev#31793)

Author: AnjoMan

doc/source/whatsnew/v1.3.0.rst

@@ -298,6 +298,7 @@ Timezones
 ^^^^^^^^^
 - Bug in different ``tzinfo`` objects representing UTC not being treated as equivalent (:issue:`39216`)
 - Bug in ``dateutil.tz.gettz("UTC")`` not being recognized as equivalent to other UTC-representing tzinfos (:issue:`39276`)
+- Bug in ``Timestamp`` and ``DatetimeIndex`` incorrectly raising a ``TypeError`` when subtracting two times that don't have the same timezone offset (:issue:`31793`)
 -
 
 Numeric

pandas/_libs/tslibs/timestamps.pyx

@@ -305,10 +305,10 @@ cdef class _Timestamp(ABCTimestamp):
             else:
                 self = type(other)(self)
 
-            # validate tz's
-            if not tz_compare(self.tzinfo, other.tzinfo):
-                raise TypeError("Timestamp subtraction must have the "
-                                "same timezones or no timezones")
+            if (self.tzinfo is None) ^ (other.tzinfo is None):
+                raise TypeError(
+                    "Cannot subtract offset-naive and offset-aware datetimes."
+                )
 
             # scalar Timestamp/datetime - Timestamp/datetime -> yields a
             # Timedelta

pandas/core/arrays/datetimes.py

@@ -712,11 +712,9 @@ def _sub_datetimelike_scalar(self, other):
         if other is NaT:
             return self - NaT
 
-        if not self._has_same_tz(other):
-            # require tz compat
-            raise TypeError(
-                "Timestamp subtraction must have the same timezones or no timezones"
-            )
+        if (self.tzinfo is None) ^ (other.tzinfo is None):
+            # require non-ambiguous timezones
+            raise TypeError("Cannot subtract offset-naive and offset-aware datetimes.")
 
         i8 = self.asi8
         result = checked_add_with_arr(i8, -other.value, arr_mask=self._isnan)

pandas/tests/arithmetic/test_timedelta64.py

@@ -1,6 +1,6 @@
 # Arithmetic tests for DataFrame/Series/Index/Array classes that should
 # behave identically.
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 
 import numpy as np
 import pytest
@@ -360,6 +360,8 @@ def test_subtraction_ops_with_tz(self):
         ts_tz2 = Timestamp("20130101").tz_localize("CET")
         dt_tz = ts_tz.to_pydatetime()
         td = Timedelta("1 days")
+        ts_utc = Timestamp("2020-10-22T22:00:00+00:00")
+        dt_utc = datetime(2020, 10, 22, 22, tzinfo=timezone.utc)
 
         def _check(result, expected):
             assert result == expected
@@ -378,36 +380,54 @@ def _check(result, expected):
         expected = Timedelta("0 days")
         _check(result, expected)
 
+        result = ts_utc - dt_utc
+        expected = Timedelta("0 days")
+        _check(result, expected)
+
+        result = dt_tz - ts_tz2
+        expected = Timedelta("0 days 06:00:00")
+        _check(result, expected)
+
+        result = ts_tz2 - dt_tz
+        expected = Timedelta("-1 days +18:00:00")
+        _check(result, expected)
+
+        # gotta chedk this
         # tz mismatches
-        msg = "Timestamp subtraction must have the same timezones or no timezones"
+        msg = "Cannot subtract offset-naive and offset-aware datetimes."
         with pytest.raises(TypeError, match=msg):
             dt_tz - ts
         msg = "can't subtract offset-naive and offset-aware datetimes"
         with pytest.raises(TypeError, match=msg):
             dt_tz - dt
-        msg = "Timestamp subtraction must have the same timezones or no timezones"
-        with pytest.raises(TypeError, match=msg):
-            dt_tz - ts_tz2
         msg = "can't subtract offset-naive and offset-aware datetimes"
         with pytest.raises(TypeError, match=msg):
             dt - dt_tz
-        msg = "Timestamp subtraction must have the same timezones or no timezones"
+        msg = "Cannot subtract offset-naive and offset-aware datetimes."
         with pytest.raises(TypeError, match=msg):
             ts - dt_tz
         with pytest.raises(TypeError, match=msg):
             ts_tz2 - ts
         with pytest.raises(TypeError, match=msg):
             ts_tz2 - dt
-        with pytest.raises(TypeError, match=msg):
-            ts_tz - ts_tz2
 
         # with dti
         with pytest.raises(TypeError, match=msg):
             dti - ts_tz
         with pytest.raises(TypeError, match=msg):
             dti_tz - ts
-        with pytest.raises(TypeError, match=msg):
-            dti_tz - ts_tz2
+
+        result = dti_tz - ts_tz2
+        expected = TimedeltaIndex(
+            ["0 days 06:00:00", "1 days 06:00:00", "2 days 06:00:00"]
+        )
+        tm.assert_index_equal(result, expected)
+
+        result = ts_tz2 - dti_tz
+        expected = TimedeltaIndex(
+            ["-1 days +18:00:00", "-2 days +18:00:00", "-3 days +18:00:00"]
+        )
+        tm.assert_index_equal(result, expected)
 
         result = dti_tz - dt_tz
         expected = TimedeltaIndex(["0 days", "1 days", "2 days"])

pandas/tests/scalar/timestamp/test_arithmetic.py

@@ -96,7 +96,7 @@ def test_rsub_dtscalars(self, tz_naive_fixture):
         if tz_naive_fixture is None:
             assert other.to_datetime64() - ts == td
         else:
-            msg = "subtraction must have"
+            msg = "Cannot subtract offset-naive and offset-aware datetimes."
             with pytest.raises(TypeError, match=msg):
                 other.to_datetime64() - ts