[Python-Dev] PEP 409 and the stdlib (original) (raw)

Steven D'Aprano steve at pearwood.info
Mon May 20 17:39:03 CEST 2013

On 21/05/13 00:12, Ethan Furman wrote:

As a case in point, base64.py is currently getting a bug fix, and also contains this code:

def b32decode(s, casefold=False, map01=None): . . . for i in range(0, len(s), 8): quanta = s[i: i + 8] acc = 0 try: for c in quanta: acc = (acc << 5) + b32rev[c] except KeyError: raise binascii.Error('Non-base32 digit found') . . . else: raise binascii.Error('Incorrect padding') Does the KeyError qualify as irrelevant noise?

IMO, it is irrelevant noise, and obviously so. The binascii.Error raised is not a bug to be fixed, it is a deliberate exception and part of the API of the binascii module. That it occurs inside an "except KeyError" block is a mere implementation detail. It merely happens to be that digits are converted by looking up in a mapping, another implementation might use a completely different mechanism. In fact, the implementation in Python 3.3 is completely different, and there is no KeyError to suppress.

In another reply, R.David Murray answered:

"I don't see that it is of benefit to suppress [the KeyError]."

Can I suggest that it's obviously been a long, long time since you were a beginner to the language, and you've forgotten how intimidating error messages can be? Error messages should be relevant. Irrelevant details don't help, they hinder, and I suggest that the KeyError is irrelevant.

-- Steven

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