ENH: improve error message when specifying a previously-deprecated frequen…

pandas/_libs/tslibs/offsets.pyx

@@ -5276,6 +5276,18 @@ def _get_offset(name: str) -> BaseOffset:
  return _offset_map[name]
 
 
+deprec_to_valid_alias = {
+ "H": "h",
+ "BH": "bh",
+ "CBH": "cbh",
+ "T": "min",
+ "S": "s",
+ "L": "ms",
+ "U": "us",
+ "N": "ns",
+}
+
+
 cpdef to_offset(freq, bint is_period=False):
  """
  Return DateOffset object from string or datetime.timedelta object.
@@ -5359,6 +5371,11 @@ cpdef to_offset(freq, bint is_period=False):
 
  tups = zip(split[0::4], split[1::4], split[2::4])
  for n, (sep, stride, name) in enumerate(tups):
+ if name in deprec_to_valid_alias:
+ raise ValueError(INVALID_FREQ_ERR_MSG.format(
+ f"{name}. Did you mean {deprec_to_valid_alias[name]}?")
+ )
+
  name = _warn_about_deprecated_aliases(name, is_period)
  _validate_to_offset_alias(name, is_period)
  if is_period:

pandas/tests/tseries/offsets/test_offsets.py

@@ -1157,6 +1157,11 @@ def test_offset_multiplication(
  tm.assert_series_equal(resultarray, expectedarray)
 
 
+def test_offset_deprecated_error():
+ with pytest.raises(ValueError, match=r"Did you mean h?"):
+ date_range("2012-01-01", periods=3, freq="H")
+
+
 def test_dateoffset_operations_on_dataframes(performance_warning):
  # GH 47953
  df = DataFrame({"T": [Timestamp("2019-04-30")], "D": [DateOffset(months=1)]})