BUG: Timestamp(2020,1, 1, tzinfo=foo) GH#31929

doc/source/whatsnew/v1.5.0.rst

@@ -119,6 +119,7 @@ Categorical
 Datetimelike
 ^^^^^^^^^^^^
 - Bug in :func:`to_datetime` with sequences of ``np.str_`` objects incorrectly raising (:issue:`32264`)
+- Bug in :class:`Timestamp` construction when passing datetime components as positional arguments and ``tzinfo`` as a keyword argument incorrectly raising (:issue:`31929`)
 -
 
 Timedelta

pandas/_libs/tslibs/timestamps.pyx

@@ -1295,6 +1295,27 @@ class Timestamp(_Timestamp):
             # GH#17690 tzinfo must be a datetime.tzinfo object, ensured
             #  by the cython annotation.
             if tz is not None:
+                if (is_integer_object(tz)
+                    and is_integer_object(ts_input)
+                    and is_integer_object(freq)
+                ):
+                    # GH#31929 e.g. Timestamp(2019, 3, 4, 5, 6, tzinfo=foo)
+                    # TODO(GH#45307): this will still be fragile to
+                    #  mixed-and-matched positional/keyword arguments
+                    ts_input = datetime(
+                        ts_input,
+                        freq,
+                        tz,
+                        unit or 0,
+                        year or 0,
+                        month or 0,
+                        day or 0,
+                        fold=fold or 0,
+                    )
+                    nanosecond = hour
+                    tz = tzinfo
+                    return cls(ts_input, nanosecond=nanosecond, tz=tz)
+
                 raise ValueError('Can provide at most one of tz, tzinfo')
 
             # User passed tzinfo instead of tz; avoid silently ignoring

pandas/tests/scalar/timestamp/test_constructors.py

@@ -2,6 +2,7 @@
 from datetime import (
     datetime,
     timedelta,
+    timezone,
 )
 
 import dateutil.tz
@@ -242,6 +243,25 @@ def test_constructor_tz_or_tzinfo(self):
         ]
         assert all(ts == stamps[0] for ts in stamps)
 
+    def test_constructor_positional_with_tzinfo(self):
+        # GH#31929
+        ts = Timestamp(2020, 12, 31, tzinfo=timezone.utc)
+        expected = Timestamp("2020-12-31", tzinfo=timezone.utc)
+        assert ts == expected
+
+    @pytest.mark.xfail(reason="GH#45307")
+    @pytest.mark.parametrize("kwd", ["nanosecond", "microsecond", "second", "minute"])
+    def test_constructor_positional_keyword_mixed_with_tzinfo(self, kwd):
+        # TODO: if we passed microsecond with a keyword we would mess up
+        #  xref GH#45307
+        kwargs = {kwd: 4}
+        ts = Timestamp(2020, 12, 31, tzinfo=timezone.utc, **kwargs)
+
+        td_kwargs = {kwd + "s": 4}
+        td = Timedelta(**td_kwargs)
+        expected = Timestamp("2020-12-31", tz=timezone.utc) + td
+        assert ts == expected
+
     def test_constructor_positional(self):
         # see gh-10758
         msg = (