[Python-Dev] TypeError messages (original) (raw)

MRAB python at mrabarnett.plus.com
Sat Feb 21 22:39:32 CET 2015

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.

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