Python re examples

basic-re.py

import re

# match requires the entire string to match, while search will
# find a partial match

assert re.match("\d+", "123")
assert not re.match("\d+", "hello 123")
assert re.search("\d+", "123")
assert re.search("\d+", "hello 123")

compiled.py

import re

# compiled regexes have match and search methods

# Note that Python has a compile cache stored in the re module
# for recently used regexes, so a program with a few static regexes
# need not compile for performance. Nonetheless it can improve
# readability.

# this example also demonstrates numbered groups

tuple_re = re.compile("\(" +
"(.*?)" + # first element
",\s*" + # separator (comma followed by whitespace)
"(.*?)" + # second element
"\)")

def tuple(s):
    m = tuple_re.match(s)
    # get groups by number (0 is entire match as usual)
    return (m.group(1), m.group(2))

assert tuple("(1,2)") == ("1","2")
assert tuple("( abc, def )") == (" abc", "def ")

named-capture.py

import re

# Named capture groups can be retrieved by name. The value is
# None if the capture group does not actually match anything.

def keyval(s):
    m = re.match("(?P<key>.*):(?P<val>(?P<header>.)?.*)", s)
    if m is None:
        return None
    return (m.group("key"), m.group("val"), m.group("header"))

assert keyval("foo:bar") == ("foo", "bar", "b")
assert keyval("foo:") == ("foo", "", None)