[Python-ideas] if-syntax for regular for-loops

[dbpokorny at gmail.com]

On Oct 10, 12:51 pm, Arnaud Delobelle <arno... at googlemail.com> wrote:
> There is also a problem with parsing as:
>
> * the following is correct:
>
>      for i in L1 if cond else L2:
>         do_something()
>
> * Python's grammar is LL(1)

Not really.

for_stmt: 'for' exprlist 'in' testlist ['if' or_test] ':' suite
['else' ':' suite]

FWIW, I think this would be an entirely different discussion if
someone did all of the work first (code+docs+test code), and THEN went
to python-dev along with two or three examples from the standard
library where the new syntax would *add* clarity.

Side note: not to discourage anyone, but I happened to look at Lib/
pydoc.py and found several examples where, due to line-length, forcing
the new syntax at every available opportunity would either
substantially reduce clarity or be more or less pointless. Here are a
couple cases so you can make up you own mind.

#1

original:

        for ext in ('.py', '.pyc', '.pyo'):
            if os.path.isfile(os.path.join(path, '__init__' + ext)):
                return True

vs. new syntax:

        for ext in ('.py', '.pyc', '.pyo') if
os.path.isfile(os.path.join(path, '__init__' + ext)):
            return True

vs. existing alternative:

        if any( os.path.isfile(os.path.join(path,'__init__' + ext))
for ext in ('.py','.pyc','.pyo')):
            return True

#2

original:

        for dict in dicts:
            if name in dict:
                return '<a href="%s">%s</a>' % (dict[name], name)

new syntax:

        for dict in dicts if name in dict:
            return '<a href="%s">%s</a>' % (dict[name], name)

Cheers,
David