[Python-Dev] Adding a conditional expression in Py3.0

[Raymond Hettinger]

> > It only takes about five minutes to try out a given syntax proposal
on
> > all the fragments listed below.  That short exercise provides an
> > excellent insight into the look and feel of each proposal in real
world
> > code.
> 
> I did this for my favorite proposal, and ended up with the list shown
> further down below.
> 
> I think they all looks great!

They mostly look great to me too :-)

The exceptions are the ones in pydoc which have an odd feel to them and,
to my eyes, don't parse well.  I can't put my finger on the issue -- it
could be that any ternary operator syntax breaks down when used in
series with other operators or when there are complex sub-expressions.


> pydoc.py:     return re.sub('^ *\n', '', rstrip(result)) if result
else ''
> pydoc.py:         anchor = (cl.__name__ if cl else '') + '-' + name
> pydoc.py:         lhs = '<strong>%s</strong> = ' % name if name else
''
> pydoc.py:         contents = [doc + '\n'] if doc else []
> pydoc.py:             line = (name + ' = ' if name else '') + repr
> pydoc.py:         line = (self.bold(name) + ' = ' if name else '') +
repr
> pydoc.py:             host = '127.0.0.1' if (sys.platform == 'mac')
else 'localhost'
> pydoc.py:             font = ('helvetica', 8 if sys.platform ==
'win32' else 10)

There is one that looks like it could be completely mis-interpreted:

   (name + ' = ' if name else '')       # as written above
   ((name + ' = ') if name else '')     # one mental interpretation
   (name + (' = ' if name else ''))     # an incorrect interpretation

The grouping issue doesn't arise for syntaxes that start with a keyword:
   (if name then name + ' = ' else '')
but even those suffer from unclear precedence when used with binary
operations on the right:   (if cond then a else b + c).  



Raymond