BUG: can't round-trip non-nano Timestamp

pandas/_libs/tslibs/conversion.pxd

@@ -42,8 +42,8 @@ cdef _TSObject convert_str_to_tsobject(str ts, tzinfo tz, str unit,
 cdef int64_t get_datetime64_nanos(object val, NPY_DATETIMEUNIT reso) except? -1
 
 cpdef datetime localize_pydatetime(datetime dt, tzinfo tz)
-cdef int64_t cast_from_unit(object ts, str unit) except? -1
-cpdef (int64_t, int) precision_from_unit(str unit)
+cdef int64_t cast_from_unit(object ts, str unit, NPY_DATETIMEUNIT out_reso=*) except? -1
+cpdef (int64_t, int) precision_from_unit(str unit, NPY_DATETIMEUNIT out_reso=*)
 
 cdef maybe_localize_tso(_TSObject obj, tzinfo tz, NPY_DATETIMEUNIT reso)
 

pandas/_libs/tslibs/conversion.pyx

@@ -1,6 +1,7 @@
 import numpy as np
 
 cimport numpy as cnp
+from libc.math cimport log10
 from numpy cimport (
     int32_t,
     int64_t,
@@ -81,7 +82,11 @@ TD64NS_DTYPE = np.dtype("m8[ns]")
 # ----------------------------------------------------------------------
 # Unit Conversion Helpers
 
-cdef int64_t cast_from_unit(object ts, str unit) except? -1:
+cdef int64_t cast_from_unit(
+        object ts,
+        str unit,
+        NPY_DATETIMEUNIT out_reso=NPY_FR_ns
+) except? -1:
     """
     Return a casting of the unit represented to nanoseconds
     round the fractional part of a float to our precision, p.
@@ -99,7 +104,7 @@ cdef int64_t cast_from_unit(object ts, str unit) except? -1:
         int64_t m
         int p
 
-    m, p = precision_from_unit(unit)
+    m, p = precision_from_unit(unit, out_reso)
 
     # just give me the unit back
     if ts is None:
@@ -119,7 +124,7 @@ cdef int64_t cast_from_unit(object ts, str unit) except? -1:
         if is_float_object(ts):
             ts = int(ts)
         dt64obj = np.datetime64(ts, unit)
-        return get_datetime64_nanos(dt64obj, NPY_FR_ns)
+        return get_datetime64_nanos(dt64obj, out_reso)
 
     # cast the unit, multiply base/frac separately
     # to avoid precision issues from float -> int
@@ -142,7 +147,10 @@ cdef int64_t cast_from_unit(object ts, str unit) except? -1:
         ) from err
 
 
-cpdef inline (int64_t, int) precision_from_unit(str unit):
+cpdef inline (int64_t, int) precision_from_unit(
+        str unit,
+        NPY_DATETIMEUNIT out_reso=NPY_DATETIMEUNIT.NPY_FR_ns,
+):
     """
     Return a casting of the unit represented to nanoseconds + the precision
     to round the fractional part.
@@ -154,45 +162,39 @@ cpdef inline (int64_t, int) precision_from_unit(str unit):
     """
     cdef:
         int64_t m
+        int64_t multiplier
         int p
         NPY_DATETIMEUNIT reso = abbrev_to_npy_unit(unit)
 
+    multiplier = periods_per_second(out_reso)
+
     if reso == NPY_DATETIMEUNIT.NPY_FR_Y:
         # each 400 years we have 97 leap years, for an average of 97/400=.2425
         #  extra days each year. We get 31556952 by writing
         #  3600*24*365.2425=31556952
-        m = 1_000_000_000 * 31556952
-        p = 9
+        m = multiplier * 31556952
     elif reso == NPY_DATETIMEUNIT.NPY_FR_M:
         # 2629746 comes from dividing the "Y" case by 12.
-        m = 1_000_000_000 * 2629746
-        p = 9
+        m = multiplier * 2629746
     elif reso == NPY_DATETIMEUNIT.NPY_FR_W:
-        m = 1_000_000_000 * 3600 * 24 * 7
-        p = 9
+        m = multiplier * 3600 * 24 * 7
     elif reso == NPY_DATETIMEUNIT.NPY_FR_D:
-        m = 1_000_000_000 * 3600 * 24
-        p = 9
+        m = multiplier * 3600 * 24
     elif reso == NPY_DATETIMEUNIT.NPY_FR_h:
-        m = 1_000_000_000 * 3600
-        p = 9
+        m = multiplier * 3600
     elif reso == NPY_DATETIMEUNIT.NPY_FR_m:
-        m = 1_000_000_000 * 60
-        p = 9
+        m = multiplier * 60
     elif reso == NPY_DATETIMEUNIT.NPY_FR_s:
-        m = 1_000_000_000
-        p = 9
+        m = multiplier
     elif reso == NPY_DATETIMEUNIT.NPY_FR_ms:
-        m = 1_000_000
-        p = 6
+        m = multiplier // 1_000
     elif reso == NPY_DATETIMEUNIT.NPY_FR_us:
-        m = 1000
-        p = 3
+        m = multiplier // 1_000_000
     elif reso == NPY_DATETIMEUNIT.NPY_FR_ns or reso == NPY_DATETIMEUNIT.NPY_FR_GENERIC:
-        m = 1
-        p = 0
+        m = multiplier // 1_000_000_000
     else:
         raise ValueError(f"cannot cast unit {unit}")
+    p = <int>log10(m)  # number of digits in 'm' minus 1
     return m, p
 
 
@@ -294,9 +296,15 @@ cdef _TSObject convert_to_tsobject(object ts, tzinfo tz, str unit,
         if ts == NPY_NAT:
             obj.value = NPY_NAT
         else:
-            ts = cast_from_unit(ts, unit)
+            if unit is None:
+                in_reso = abbrev_to_npy_unit("ns")
+            else:
+                in_reso = abbrev_to_npy_unit(unit)
+            reso = get_supported_reso(in_reso)
+            ts = cast_from_unit(ts, unit, reso)
             obj.value = ts
-            pandas_datetime_to_datetimestruct(ts, NPY_FR_ns, &obj.dts)
+            obj.creso = reso
+            pandas_datetime_to_datetimestruct(ts, reso, &obj.dts)
     elif is_float_object(ts):
         if ts != ts or ts == NPY_NAT:
             obj.value = NPY_NAT

pandas/tests/scalar/timestamp/test_constructors.py

@@ -76,7 +76,7 @@ def test_constructor_from_date_second_reso(self):
     @pytest.mark.parametrize("typ", [int, float])
     def test_construct_from_int_float_with_unit_out_of_bound_raises(self, typ):
         # GH#50870  make sure we get a OutOfBoundsDatetime instead of OverflowError
-        val = typ(150000000)
+        val = typ(150000000000000)
 
         msg = f"cannot convert input {val} with the unit 'D'"
         with pytest.raises(OutOfBoundsDatetime, match=msg):

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -996,6 +996,12 @@ def test_resolution(self, ts):
         assert result == expected
         assert result._creso == expected._creso
 
+    def test_out_of_ns_bounds(self):
+        # https://github.com/pandas-dev/pandas/issues/51060
+        result = Timestamp(-52700112000, unit="s")
+        assert result == Timestamp("0300-01-01")
+        assert result.to_numpy() == np.datetime64("0300-01-01T00:00:00", "s")
+
 
 def test_timestamp_class_min_max_resolution():
     # when accessed on the class (as opposed to an instance), we default

pandas/tests/tools/test_to_datetime.py

@@ -1767,11 +1767,11 @@ def test_unit(self, cache):
             to_datetime([1], unit="D", format="%Y%m%d", cache=cache)
 
     def test_unit_array_mixed_nans(self, cache):
-        values = [11111111, 1, 1.0, iNaT, NaT, np.nan, "NaT", ""]
+        values = [11111111111111111, 1, 1.0, iNaT, NaT, np.nan, "NaT", ""]
         result = to_datetime(values, unit="D", errors="ignore", cache=cache)
         expected = Index(
             [
-                11111111,
+                11111111111111111,
                 Timestamp("1970-01-02"),
                 Timestamp("1970-01-02"),
                 NaT,
@@ -1790,22 +1790,22 @@ def test_unit_array_mixed_nans(self, cache):
         )
         tm.assert_index_equal(result, expected)
 
-        msg = "cannot convert input 11111111 with the unit 'D'"
+        msg = "cannot convert input 11111111111111111 with the unit 'D'"
         with pytest.raises(OutOfBoundsDatetime, match=msg):
             to_datetime(values, unit="D", errors="raise", cache=cache)
 
     def test_unit_array_mixed_nans_large_int(self, cache):
-        values = [1420043460000, iNaT, NaT, np.nan, "NaT"]
+        values = [1420043460000000000000000, iNaT, NaT, np.nan, "NaT"]
 
         result = to_datetime(values, errors="ignore", unit="s", cache=cache)
-        expected = Index([1420043460000, NaT, NaT, NaT, NaT], dtype=object)
+        expected = Index([1420043460000000000000000, NaT, NaT, NaT, NaT], dtype=object)
         tm.assert_index_equal(result, expected)
 
         result = to_datetime(values, errors="coerce", unit="s", cache=cache)
         expected = DatetimeIndex(["NaT", "NaT", "NaT", "NaT", "NaT"])
         tm.assert_index_equal(result, expected)
 
-        msg = "cannot convert input 1420043460000 with the unit 's'"
+        msg = "cannot convert input 1420043460000000000000000 with the unit 's'"
         with pytest.raises(OutOfBoundsDatetime, match=msg):
             to_datetime(values, errors="raise", unit="s", cache=cache)