[Python-Dev] TypeError messages

[MRAB]

On 2015-02-21 17:14, Antoine Pitrou wrote:
> On Fri, 20 Feb 2015 14:05:11 +0000
> Brett Cannon <brett at python.org> wrote:
>> 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".
>
> If we are busy nitpicking, why are we saying "found Y"? Nothing was
> *found* by the callee, it just *got* an argument.
>
Well, it depends on the reason for the message.

If you're passing an argument, then 'found' is the wrong word, but if
you're parsing, say, a regex, then 'got' is the wrong word.

> So it should be "expected X, but got Y".
>
> Personally, I think the "but" is superfluous: the contradiction is
> already implied, so "expected X, got Y" is terser and conveys the
> meaning just as well.
>
If you wanted a message to cover both argument-passing and parsing,
then "expected Y, not Y" would do.