raise FutureWarning instead of ValueError

Author: natmokval

doc/source/whatsnew/v2.1.0.rst

@@ -279,6 +279,7 @@ Deprecations
 - Deprecated constructing :class:`SparseArray` from scalar data, pass a sequence instead (:issue:`53039`)
 - Deprecated option "mode.use_inf_as_na", convert inf entries to ``NaN`` before instead (:issue:`51684`)
 - Deprecated positional indexing on :class:`Series` with :meth:`Series.__getitem__` and :meth:`Series.__setitem__`, in a future version ``ser[item]`` will *always* interpret ``item`` as a label, not a position (:issue:`50617`)
+- Deprecated strings ``T``, ``t``, ``L`` and ``l`` denoting units in :func:`to_timedelta` (:issue:`52536`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_210.performance:

pandas/_libs/tslibs/dtypes.pyx

@@ -379,14 +379,10 @@ cpdef NPY_DATETIMEUNIT abbrev_to_npy_unit(str abbrev):
         return NPY_DATETIMEUNIT.NPY_FR_h
     elif abbrev == "m":
         return NPY_DATETIMEUNIT.NPY_FR_m
-    elif abbrev == "T"  or abbrev == "t":
-        return NPY_DATETIMEUNIT.NPY_FR_m
     elif abbrev == "s":
         return NPY_DATETIMEUNIT.NPY_FR_s
     elif abbrev == "ms":
         return NPY_DATETIMEUNIT.NPY_FR_ms
-    elif abbrev == "L"  or abbrev == "l":
-        return NPY_DATETIMEUNIT.NPY_FR_ms
     elif abbrev == "us":
         return NPY_DATETIMEUNIT.NPY_FR_us
     elif abbrev == "ns":

pandas/_libs/tslibs/timedeltas.pyi

@@ -37,8 +37,8 @@ UnitChoices = Literal[
     "minute",
     "min",
     "minutes",
-    "t",
     "T",
+    "t",
     "s",
     "seconds",
     "sec",
@@ -48,8 +48,8 @@ UnitChoices = Literal[
     "millisecond",
     "milli",
     "millis",
-    "l",
     "L",
+    "l",
     "us",
     "microseconds",
     "microsecond",

pandas/_libs/tslibs/timedeltas.pyx

@@ -123,6 +123,7 @@ cdef dict timedelta_abbrevs = {
     "minute": "m",
     "min": "m",
     "minutes": "m",
+    "T": "m",
     "t": "m",
     "s": "s",
     "seconds": "s",
@@ -133,6 +134,7 @@ cdef dict timedelta_abbrevs = {
     "millisecond": "ms",
     "milli": "ms",
     "millis": "ms",
+    "L": "ms",
     "l": "ms",
     "us": "us",
     "microseconds": "us",
@@ -722,7 +724,7 @@ cpdef inline str parse_timedelta_unit(str unit):
     """
     if unit is None:
         return "ns"
-    elif unit in {"M", "t", "T", "l", "L"}:
+    elif unit == "M":
         return unit
     try:
         return timedelta_abbrevs[unit.lower()]

pandas/core/tools/timedeltas.py

@@ -7,6 +7,7 @@
     TYPE_CHECKING,
     overload,
 )
+import warnings
 
 import numpy as np
 
@@ -19,6 +20,7 @@
     Timedelta,
     parse_timedelta_unit,
 )
+from pandas.util._exceptions import find_stack_level
 
 from pandas.core.dtypes.common import is_list_like
 from pandas.core.dtypes.generic import (
@@ -110,14 +112,17 @@ def to_timedelta(
         * 'W'
         * 'D' / 'days' / 'day'
         * 'hours' / 'hour' / 'hr' / 'h'
-        * 'm' / 'minute' / 'min' / 'minutes'
+        * 'm' / 'minute' / 'min' / 'minutes' / 'T'
         * 'S' / 'seconds' / 'sec' / 'second'
-        * 'ms' / 'milliseconds' / 'millisecond' / 'milli' / 'millis'
+        * 'ms' / 'milliseconds' / 'millisecond' / 'milli' / 'millis' / 'L'
         * 'us' / 'microseconds' / 'microsecond' / 'micro' / 'micros' / 'U'
         * 'ns' / 'nanoseconds' / 'nano' / 'nanos' / 'nanosecond' / 'N'
 
         Must not be specified when `arg` context strings and ``errors="raise"``.
 
+        .. deprecated:: 2.1.0
+            Units 'T' and 'L' are deprecated and will be removed in a future version.
+
     errors : {'ignore', 'raise', 'coerce'}, default 'raise'
         - If 'raise', then invalid parsing will raise an exception.
         - If 'coerce', then invalid parsing will be set as NaT.
@@ -181,8 +186,12 @@ def to_timedelta(
             "represent unambiguous timedelta values durations."
         )
 
-    if unit in {"t", "T", "l", "L"}:
-        raise ValueError("Units 't', 'T', 'l' and 'L' are no longer supported.")
+    if unit in {"T", "t", "L", "l"}:
+        warnings.warn(
+            f"Unit {unit} is deprecated and will be removed in a future version.",
+            FutureWarning,
+            stacklevel=find_stack_level(),
+        )
 
     if arg is None:
         return arg