DEV: Improves Error msg when constructing a Timedelta

doc/source/whatsnew/v2.1.0.rst

@@ -111,6 +111,7 @@ Other enhancements
 - Improve error message when setting :class:`DataFrame` with wrong number of columns through :meth:`DataFrame.isetitem` (:issue:`51701`)
 - Improved error handling when using :meth:`DataFrame.to_json` with incompatible ``index`` and ``orient`` arguments (:issue:`52143`)
 - Improved error message when creating a DataFrame with empty data (0 rows), no index and an incorrect number of columns. (:issue:`52084`)
+- Improved error message when creating a Timedelta from a ambiguous time period (:issue:`54059`)
 - Let :meth:`DataFrame.to_feather` accept a non-default :class:`Index` and non-string column names (:issue:`51787`)
 - Performance improvement in :func:`read_csv` (:issue:`52632`) with ``engine="c"``
 - :meth:`Categorical.from_codes` has gotten a ``validate`` parameter (:issue:`50975`)

pandas/_libs/tslibs/timedeltas.pyx

@@ -1843,7 +1843,10 @@ class Timedelta(_Timedelta):
                              NPY_DATETIMEUNIT.NPY_FR_W,
                              NPY_DATETIMEUNIT.NPY_FR_GENERIC]):
                 err = npy_unit_to_abbrev(reso)
-                raise ValueError(f" cannot construct a Timedelta from a unit {err}")
+                raise ValueError(
+                    f"Unit {err} is not supported. "
+                    "Only unambiguous timedelta values durations are supported. "
+                    "Allowed units are 'W', 'D', 'h', 'm', 's', 'ms', 'us', 'ns'")
 
             new_reso = get_supported_reso(reso)
             if reso != NPY_DATETIMEUNIT.NPY_FR_GENERIC:

pandas/tests/tslibs/test_timedeltas.py

@@ -76,7 +76,10 @@ def test_delta_to_nanoseconds_td64_MY_raises():
 def test_unsupported_td64_unit_raises(unit):
     # GH 52806
     with pytest.raises(
-        ValueError, match=f"cannot construct a Timedelta from a unit {unit}"
+        ValueError,
+        match=f"Unit {unit} is not supported. "
+        "Only unambiguous timedelta values durations are supported. "
+        "Allowed units are 'W', 'D', 'h', 'm', 's', 'ms', 'us', 'ns'",
     ):
         Timedelta(np.timedelta64(1, unit))