[Python-Dev] TypeError messages

[Brett Cannon]

On Fri Feb 20 2015 at 10:27:35 AM Stefan Richthofer <
Stefan.Richthofer at gmx.de> wrote:

> Honestly, the right solution would be to have a function or macro that
> generates the TypeError messages
> from X, Y, Z arguments. (Until now I actually believed this would be
> already the case)
> - type errors would be of uniform style
> - if for some reoson the format should be changed, this can be done in one
> central place
> - if someone would want to parse the error message this would be feasible
> I suppose it should be straight forward to find error message creations in
> the source by searching for "TypeError" or something.
> Maybe this kind of cleanup could be done along with the implementation of
> PEP 484?
>

Actually PEP 473 covers standardizing error messages by introducing
keyword-only arguments which would lead to a standardized message being
generated. From the C side there can be a function provided to make it easy
to get the same result as constructing the exception with the keyword-only
argument.

-Brett


>
> -Stefan
>
> *Gesendet:* Freitag, 20. Februar 2015 um 15:05 Uhr
> *Von:* "Brett Cannon" <brett at python.org>
> *An:* "Serhiy Storchaka" <storchaka at gmail.com>, python-dev at python.org
> *Betreff:* Re: [Python-Dev] TypeError messages
>
> On Thu Feb 19 2015 at 5:52:07 PM Serhiy Storchaka <storchaka at gmail.com>
> wrote:
>>
>> Different patterns for TypeError messages are used in the stdlib:
>>
>>      expected X, Y found
>>      expected X, found Y
>>      expected X, but Y found
>>      expected X instance, Y found
>>      X expected, not Y
>>      expect X, not Y
>>      need X, Y found
>>      X is required, not Y
>>      Z must be X, not Y
>>      Z should be X, not Y
>>
>> and more.
>>
>> What the pattern is most preferable?
>
>
> My preference is for "expected X, but found Y".
>
>
>>
>> Some messages use the article before X or Y. Should the article be used
>> or omitted?
>>
>> Some messages (only in C) truncate actual type name (%.50s, %.80s,
>> %.200s, %.500s). Should type name be truncated at all and for how limit?
>
>
> I assume this is over some worry of string size blowing out memory
> allocation or something? If someone can show that's an actual worry then
> fine, otherwise I say don't truncate.
>
>
>> Type names newer truncated in TypeError messages raised in Python code.
>>
>> Some messages enclose actual type name with single quotes ('%s',
>> '%.200s'). Should type name be quoted? It is uncommon if type name
>> contains spaces.
>
>
>  I agree that type names don't need to be quoted.
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