Python 3 - RegEx

Last Updated: 2021-11-19

Most Frequently Used: match, search and findall

• re.match(): only match at the beginning of the string, returns a match object
• re.search(): locate a match anywhere in string, returns a match object
• re.findall(): find all occurrences, returns a list of strings

>>> type(re.search("foo", "foobarfoo"))
<class '_sre.SRE_Match'>
>>> type(re.match("foo", "foobarfoo"))
<class '_sre.SRE_Match'>

Extract

re.match()/re.search()

re.match() and re.search() return a match object:

>>> match = re.search("f(.*?),", "foo,faa,fuu,bar")
>>> match.groups()
('oo',)

match.group(0) returns the string snippet that matches the pattern:

>>> match.group(0)
'foo,'

other group captures the ones in ():

>>> match.group(1)
'oo'

re.findall()

re.findall() returns a list, extract value using []:

>>> match = re.findall("f(.*?),", "foo,faa,fuu,bar")
>>> match
['oo', 'aa', 'uu']
>>> match[0]
'oo'

Compiled Patterns

pattern = re.compile(pattern_string)
result = pattern.match(string)

is equivalent to

result = re.match(pattern_string, string)

re.compile() returns a SRE_Pattern object:

>>> type(re.compile("pattern"))
<class '_sre.SRE_Pattern'>

Notes

dot matches everything except newlines