[Python-ideas] for/else syntax

[Stephen J. Turnbull]

Michael Foord writes:

 > > +1.  File an RFE against PyLint for sure, and against Python too.
 > > That's a *great* idea!
 > 
 > Nonsense - there are several other ways to break out of a loop. Raising an
 > exception or returning for example.

Sure.  Maybe I'm missing something, but consider

    for x in xs:
        function_that_may_return_or_raise(x,xs)
    function_that_should_not_be_executed_in_exceptional_case(xs)

Now, a return or raise cannot cause f_t_s_n_b_e_i_e_c to be
executed; only a break can.[1]  Only a break *needs* else.

If you can give a stylistic rule to distinguish when that code should
be spelled instead

    for x in xs:
        function_that_may_return_or_raise(x,xs)
    else:
        function_that_should_not_be_executed_in_exceptional_case(xs)

then I agree.  However, if you can't, I can't either, and I can offer
no reason why we shouldn't warn about breakless for-else loops since
they are very often not what the user wants, and if they are desired,
they can be spelled equally well without else.


Footnotes: 
[1]  StopIteration can, but I thought raising StopIteration in user
code is considered quite bad form.