How do you translate this regular-expression idiom from Perl into Python?

Using named groups and a dispatch table:

r = re.compile(r'(?P<cmd>foo|bar|baz)(?P<data>.+)')

def do_foo(data):
    ...

def do_bar(data):
    ...

def do_baz(data):
    ...

dispatch = {
    'foo': do_foo,
    'bar': do_bar,
    'baz': do_baz,
}


m = r.match(var)
if m:
    dispatch[m.group('cmd')](m.group('data'))

With a little bit of introspection you can auto-generate the regexp and the dispatch table.

r"""
This is an extension of the re module. It stores the last successful
match object and lets you access it's methods and attributes via
this module.

This module exports the following additional functions:
    expand  Return the string obtained by doing backslash substitution on a
            template string.
    group   Returns one or more subgroups of the match.
    groups  Return a tuple containing all the subgroups of the match.
    start   Return the indices of the start of the substring matched by
            group.
    end     Return the indices of the end of the substring matched by group.
    span    Returns a 2-tuple of (start(), end()) of the substring matched
            by group.

This module defines the following additional public attributes:
    pos         The value of pos which was passed to the search() or match()
                method.
    endpos      The value of endpos which was passed to the search() or
                match() method.
    lastindex   The integer index of the last matched capturing group.
    lastgroup   The name of the last matched capturing group.
    re          The regular expression object which as passed to search() or
                match().
    string      The string passed to match() or search().
"""

import re as re_

from re import *
from functools import wraps

__all__ = re_.__all__ + [ "expand", "group", "groups", "start", "end", "span",
        "last_match", "pos", "endpos", "lastindex", "lastgroup", "re", "string" ]

last_match = pos = endpos = lastindex = lastgroup = re = string = None

def _set_match(match=None):
    global last_match, pos, endpos, lastindex, lastgroup, re, string
    if match is not None:
        last_match = match
        pos = match.pos
        endpos = match.endpos
        lastindex = match.lastindex
        lastgroup = match.lastgroup
        re = match.re
        string = match.string
    return match

@wraps(re_.match)
def match(pattern, string, flags=0):
    return _set_match(re_.match(pattern, string, flags))


@wraps(re_.search)
def search(pattern, string, flags=0):
    return _set_match(re_.search(pattern, string, flags))

@wraps(re_.findall)
def findall(pattern, string, flags=0):
    matches = re_.findall(pattern, string, flags)
    if matches:
        _set_match(matches[-1])
    return matches

@wraps(re_.finditer)
def finditer(pattern, string, flags=0):
    for match in re_.finditer(pattern, string, flags):
        yield _set_match(match)

def expand(template):
    if last_match is None:
        raise TypeError, "No successful match yet."
    return last_match.expand(template)

def group(*indices):
    if last_match is None:
        raise TypeError, "No successful match yet."
    return last_match.group(*indices)

def groups(default=None):
    if last_match is None:
        raise TypeError, "No successful match yet."
    return last_match.groups(default)

def groupdict(default=None):
    if last_match is None:
        raise TypeError, "No successful match yet."
    return last_match.groupdict(default)

def start(group=0):
    if last_match is None:
        raise TypeError, "No successful match yet."
    return last_match.start(group)

def end(group=0):
    if last_match is None:
        raise TypeError, "No successful match yet."
    return last_match.end(group)

def span(group=0):
    if last_match is None:
        raise TypeError, "No successful match yet."
    return last_match.span(group)

del wraps  # Not needed past module compilation

For example:

if gre.match("foo(.+)", var):
  # do something with gre.group(1)
elif gre.match("bar(.+)", var):
  # do something with gre.group(1)
elif gre.match("baz(.+)", var):
  # do something with gre.group(1)

Yeah, it's kind of annoying. Perhaps this will work for your case.

import re

class ReCheck(object):
    def __init__(self):
        self.result = None
    def check(self, pattern, text):
        self.result = re.search(pattern, text)
        return self.result

var = 'bar stuff'
m = ReCheck()
if m.check(r'foo(.+)',var):
    print m.result.group(1)
elif m.check(r'bar(.+)',var):
    print m.result.group(1)
elif m.check(r'baz(.+)',var):
    print m.result.group(1)

EDIT: Brian correctly pointed out that my first attempt did not work. Unfortunately, this attempt is longer.

I'd suggest this, as it uses the least regex to accomplish your goal. It is still functional code, but no worse then your old Perl.

import re
var = "barbazfoo"

m = re.search(r'(foo|bar|baz)(.+)', var)
if m.group(1) == 'foo':
    print m.group(1)
    # do something with m.group(1)
elif m.group(1) == "bar":
    print m.group(1)
    # do something with m.group(1)
elif m.group(1) == "baz":
    print m.group(2)
    # do something with m.group(2)

Starting Python 3.8, and the introduction of assignment expressions (PEP 572) (:= operator), we can now capture the condition value re.search(pattern, text) in a variable match in order to both check if it's not None and then re-use it within the body of the condition:

if match := re.search(r'foo(.+)', text):
  # do something with match.group(1)
elif match := re.search(r'bar(.+)', text):
  # do something with match.group(1)
elif match := re.search(r'baz(.+)', text)
  # do something with match.group(1)

Alternatively, something not using regular expressions at all:

prefix, data = var[:3], var[3:]
if prefix == 'foo':
    # do something with data
elif prefix == 'bar':
    # do something with data
elif prefix == 'baz':
    # do something with data
else:
    # do something with var

Whether that is suitable depends on your actual problem. Don't forget, regular expressions aren't the swiss army knife that they are in Perl; Python has different constructs for doing string manipulation.

def find_first_match(string, *regexes):
    for regex, handler in regexes:
        m = re.search(regex, string):
        if m:
            handler(m)
            return
    else:
        raise ValueError

find_first_match(
    foo, 
    (r'foo(.+)', handle_foo), 
    (r'bar(.+)', handle_bar), 
    (r'baz(.+)', handle_baz))

To speed it up, one could turn all regexes into one internally and create the dispatcher on the fly. Ideally, this would be turned into a class then.

Here's the way I solved this issue:

matched = False;

m = re.match("regex1");
if not matched and m:
    #do something
    matched = True;

m = re.match("regex2");
if not matched and m:
    #do something else
    matched = True;

m = re.match("regex3");
if not matched and m:
    #do yet something else
    matched = True;

Not nearly as clean as the original pattern. However, it is simple, straightforward and doesn't require extra modules or that you change the original regexs.

import re

s = '1.23 Million equals to 1230000'

s = re.sub("([\d.]+)(\s*)Million", lambda m: str(round(float(m.groups()[0]) * 1000_000))+m.groups()[1], s)

print(s)

1230000 equals to 1230000