How can I use a custom Python linter for a specific project with flycheck?

Question

I'd like to use twistedchecker when working on the Twisted project.

Twisted has somewhat unusual coding standards that aren't mutually compatible with PEP 8 (e.g. a mandatory three line gap between top-level definitions) so I would like the pylint checkers to be disabled and run only the twistedchecker and pyflakes checkers.

I've tried setting flycheck-python-pylint-executable to "twistedchecker" in my .dir-locals.el file, but that does not seem to change the output. (I have confirmed that it is set correctly).

I suspect that the answer is that I should write my own flycheck checker. There are plenty of examples of how to do this, so that should be OK. What I don't know is:

• is there an easier way?
• if not, how would I tell flycheck to use the twisted checker for files in ~/src/Twisted/?

I have also posted this question to the Twisted-Python mailing list.

Answer 1

Indeed, you must write your own python-twisted syntax checker [1]. There is no easier way—actually I think it's already pretty easy to write Flycheck checkers. You don't even need to look at extensions for examples: You can just look at the syntax checkers in Flycheck itself.

Flycheck provides flycheck-checker to explicitly select a specific syntax checker for a buffer. To use a specific syntax checker for all buffers in a project simply set flycheck-checker via directory variables. In other words, add src/Twisted/.dir-locals.el with the following contents:

((python-mode
  (flycheck-checker . python-twisted)))

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[1] I wonder how you got the idea that changing the Pylint executable to an entirely unrelated program could possibly work…