Python's re module - saving state?

Question

One of the biggest annoyances I find in Python is the inability of the re module to save its state without explicitly doing it in a match object. Often, one needs to parse lines and if they comply a certain regex take out values from them by the same regex. I would like to write code like this:

if re.match('foo (\w+) bar (\d+)', line):
  # do stuff with .group(1) and .group(2)
elif re.match('baz whoo_(\d+)', line):
  # do stuff with .group(1)
# etc.

But unfortunately it's impossible to get to the matched object of the previous call to re.match, so this is written like this:

m = re.match('foo (\w+) bar (\d+)', line)
if m:
  # do stuff with m.group(1) and m.group(2)
else:
  m = re.match('baz whoo_(\d+)', line)
  if m:
    # do stuff with m.group(1)

Which is rather less convenient and gets really unwieldy as the list of elifs grows longer.

A hackish solution would be to wrap the re.match and re.search in my own objects that keep state somewhere. Has anyone used this? Are you aware of semi-standard implementations (in large frameworks or something)?

What other workarounds can you recommend? Or perhaps, am I just misusing the module and could achieve my needs in a cleaner way?

Thanks in advance

Answer 1

Python 3.8 has now provided us with a neat solution: := (the walrus operator).

It will assign the right-hand value to the left-hand variable, then return the value.

Basically, we can finally fulfill @aaron's wish and simply write:

if m := re.match('foo (\w+) bar (\d+)', line):
  # do stuff with m.group(1) and m.group(2)
elif m := re.match('baz whoo_(\d+)', line):
  # do stuff with m.group(1)
elif ...