[Python-ideas] Pre-conditions and post-conditions

Greg Ewing greg.ewing at canterbury.ac.nz
Mon Sep 3 18:50:27 EDT 2018

Jonathan Fine wrote:
> I've just read and article which makes a good case for providing 
> pre-conditions and post-conditions.
> http://pgbovine.net/python-unreadable.htm

There's nothing in there that talks about PBC-style executable
preconditions and postconditions, it's all about documenting
the large-scale intent and purpose of code. He doesn't put
forward any argument why executable code should be a better
way to do that than writing comments.

Personally I don't think it is. E.g.

     def distim(doshes):
        for d in doshes:
            assert isinstance(d, Dosh)
        # do something here
        for d in doshes:
            assert is_distimmed(d)

This ticks the precondition and postcondition boxes, but
still doesn't give you any idea what a Dosh is and why
you would want to distim it.


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