How to concisely cascade through multiple regex statements in Python

Question

My dilemma: I'm passing my function a string that I need to then perform numerous regex manipulations on. The logic is if there's a match in the first regex, do one thing. If no match, check for a match with the second and do something else, if not check the third, and so forth. I could do something like this:

if re.match('regex1', string):
    match = re.match('regex1', string)
    # Manipulate match.group(n) and return
elif re.match('regex2', string):
    match = re.match('regex2', string)
    # Do second manipulation
[etc.]

However, this feels unnecessarily verbose, and usually when that's the case it means there's a better way that I'm either overlooking or don't yet know about.

Does anyone have a suggestion for a better way to do this (better from a code-appearance standpoint, a memory usage standpoint, or both)?

Answer 1

Generally speaking, in these sorts of situations, you want to make the code "data driven". That is, put the important information in a container, and loop through it.

In your case, the important information is (string, function) pairs.

import re

def fun1():
    print('fun1')

def fun2():
    print('fun2')

def fun3():
    print('fun3')

regex_handlers = [
    (r'regex1', fun1),
    (r'regex2', fun2),
    (r'regex3', fun3)
    ]

def example(string):
    for regex, fun in regex_handlers:
        if re.match(regex, string):
            fun()  # call the function
            break

example('regex2')

Answer 2

Similar question from back in september: How do you translate this regular-expression idiom from Perl into Python?

Using global variables in a module maybe not the best way to do it, but converting it into a class:

import re

class Re(object):
  def __init__(self):
    self.last_match = None
  def match(self,pattern,text):
    self.last_match = re.match(pattern,text)
    return self.last_match
  def search(self,pattern,text):
    self.last_match = re.search(pattern,text)
    return self.last_match

gre = Re()
if gre.match(r'foo',text):
  # do something with gre.last_match
elif gre.match(r'bar',text):
  # do something with gre.last_match
else:
  # do something else