C-like assignment expression?

[Paddy]

On May 21, 10:38 am, boblat... at googlemail.com wrote:
> Hello,
>
> I have an if-elif chain in which I'd like to match a string against
> several regular expressions. Also I'd like to use the match groups
> within the respective elif... block. The C-like idiom that I would
> like to use is this:
>
> if (match = my_re1.match(line):
>   # use match
> elsif (match = my_re2.match(line)):
>   # use match
> elsif (match = my_re3.match(line))
>   # use match
>
> ...buy this is illegal in python. The other way is to open up an else:
> block in each level, do the assignment and then the test. This
> unneccessarily leads to deeper and deeper nesting levels which I find
> ugly. Just as ugly as first testing against the RE in the elif: clause
> and then, if it matches, to re-evaluate the RE to access the match
> groups.
>
> Thanks,
> robert

You could use named groups to search for all three patterns at once
like this:


original:

  prog1 = re.compile(r'pat1')
  prog2 = re.compile(r'pat2')
  prog3 = re.compile(r'pat3')
  ...

Becomes:

  prog = re.compile(r'(?P<p1>pat1)|(?P<p2>pat2)|(?P<p3>pat3)')
  match = prog.match(line)
  for p in 'p1 p2 p3'.split():
    if match.groupdict()[p]:
      do_something_for_prog(p)


- Paddy.