[Python-Dev] PEP 559 - built-in noop()

[Steven D'Aprano]

On Mon, Sep 11, 2017 at 07:39:07AM +1000, Chris Angelico wrote:

[...]
> As a language change, definitely not. But I like this idea for
> PYTHONBREAKPOINT. You set it to the name of a function, or to "pass"
> if you want nothing to be done. It's a special case that can't
> possibly conflict with normal usage.

I disagree -- its a confusion of concepts. "pass" is a do-nothing 
statement, not a value, so you can't set something to pass. Expect a lot 
of StackOverflow questions asking why this doesn't work:

sys.breakpoint = pass

In fact, in one sense pass is not even a statement. It has no runtime 
effect, it isn't compiled into any bytecode. It is a purely syntactic 
feature to satisfy the parser.

Of course env variables are actually strings, so we can choose "pass" to 
mean "no break point" if we wanted. But I think there are already two 
perfectly good candidates for that usage which don't mix the concepts of 
statements and values, the empty string, and None:

setenv PYTHONBREAKPOINT=""
setenv PYTHONBREAKPOINT=None


-- 
Steve