Match a line with multiple regex using Python

Question

Is there a way to see if a line contains words that matches a set of regex pattern? If I have [regex1, regex2, regex3], and I want to see if a line matches any of those, how would I do this? Right now, I am using re.findall(regex1, line), but it only matches 1 regex at a time.

score 51 · Accepted Answer · edited Oct 24 '21 at 22:05

You can use the built in functions any (or all if all regexes have to match) and a Generator expression to cycle through all the regex objects.

any (regex.match(line) for regex in [regex1, regex2, regex3])

(or any(re.match(regex_str, line) for regex in [regex_str1, regex_str2, regex_str2]) if the regexes are not pre-compiled regex objects, of course)

However, that will be inefficient compared to combining your regexes in a single expression. If this code is time- or CPU-critical, you should try instead to compose a single regular expression that encompasses all your needs, using the special | regex operator to separate the original expressions.

A simple way to combine all the regexes is to use the string join method:

re.match("|".join([regex_str1, regex_str2, regex_str2]), line)

A warning about combining the regexes in this way: It can result in wrong expressions if the original ones already do make use of the | operator.

You can make the join method less likely to fail if you wrap each expression in parenthesis. `'(' + ')|('.join(['foo', 'bar', 'baz']) + ')'` gives `'(foo)|(bar)|(baz)'`. — Brigand, Jan 17 '12 at 02:02
Better yet, wrap in `(?:...)`, and put the string together in a way that highlights its logical structure. `'|'.join('(?:{0})'.format(x) for x in ('foo', 'bar', 'baz'))` for example. — Karl Knechtel, Jan 17 '12 at 02:53

score 7 · Answer 2 · answered Jan 17 '12 at 01:27

7

Try this new regex: (regex1)|(regex2)|(regex3). This will match a line with any of the 3 regexs in it.

answered Jan 17 '12 at 01:27

jok3rnaut

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1
10

1

`(?:...)` is probably a better idea than `(...)` here, to avoid creating spurious capture groups. – Karl Knechtel Jan 17 '12 at 02:52
1

@Karl ...unless you want to check the truthiness of `.group(n)` to determine *which* group you captured. – Kyle Strand Aug 08 '14 at 21:12
@Karl Can you elaborate your comment? what you means by spurious groups? – keramat Oct 18 '19 at 05:51
like, groups that are unwanted, not helpful for solving the problem. I think I may have used the word incorrectly. But also that was over 7 years ago. – Karl Knechtel Oct 18 '19 at 06:36

score 7 · Answer 3 · answered Jan 17 '12 at 01:31

You cou loop through the regex items and do a search.

regexList = [regex1, regex2, regex3]

line = 'line of data'
gotMatch = False
for regex in regexList:
    s = re.search(regex,line)
    if s:
         gotMatch = True
         break

if gotMatch:
    doSomething()

Harry Pye · Answer 4 · 2020-02-24T14:02:24.523

1

#quite new to python but had the same problem. made this to find all with multiple 
#regular #expressions.

    regex1 = r"your regex here"
    regex2 = r"your regex here"     
    regex3 = r"your regex here"
    regexList = [regex1, regex1, regex3]

    for x in regexList:
    if re.findall(x, your string):
        some_list = re.findall(x, your string)     
        for y in some_list:
            found_regex_list.append(y)#make a list to add them to.

edited Feb 24 '20 at 14:02

answered Feb 24 '20 at 13:57

Harry Pye

11
2

you should include an explanation with your code snippet – Kevin Feb 24 '20 at 14:32

Match a line with multiple regex using Python

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