BUG: bdate_range with "cbh" fails

[natmokval]

• closes BUG: bdate_range with cbh fails #62849
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added an entry in the latest doc/source/whatsnew/v3.0.0.rst file.

we deprecated the frequency "CBH" in favor of "cbh". Now bdate_range raises for both "CBH" and "cbh". Corrected the bdate_range to work on "cbh".

[jbrockmendel]

do we want to allow strings that start with uppercase "C"? or just lowercase?

[natmokval]

@jbrockmendel, thanks for reviewing this PR.
I think we want to cover both cases, strings start with "C" and with "c", because bdate_range should work for all custom frequencies.

I would prefer to do an explicit check on line 1136, like freq in ["CBMS", "CBME", "C", "cbh"]. In this case, there’s no reason to keep the exception block below.

pandas/pandas/core/indexes/datetimes.py

Lines 1140 to 1142 in c9d96a7

	except (KeyError, TypeError) as err:
	msg = f"invalid custom frequency string: {freq}"
	raise ValueError(msg) from err

We should also update the error message in the test_all_custom_freq.
Do you think, it is better to check explicit insted of freq.upper().startswith("C")?

[jbrockmendel]

i guess if they pass an upper-case the ideal thing would be an exception message telling them specifically to do lower case? im happy to defer to your judgement on this

[natmokval]

i guess if they pass an upper-case the ideal thing would be an exception message telling them specifically to do lower case? im happy to defer to your judgement on this

I agree, for incorrect casing we could raise an error message and suggest correct casing. It seems we only have one incorrect casing for custom frequencies: "CBH". Other cases like "cbme", "c" or "Cbh" we consider as invalid frequencies.

I will make changes and add the specific exception message with suggestion to do lower case for "CBH".