Python: Regex Object and Methods

By Xah Lee. Date: . Last updated: .

Compile Regex Object

re.compile(regexStr)
Compiles regexStr into a object. A regex object can be used by regex object methods. For example, RegexObj.search(…).
re.compile(regexStr, flags)
Use flags. [see Python: Regex Flags]

The use of regex object is similar to re module functions. For example, the following 2 have the same result.

Creating a regex object is useful when you need to use the same pattern on many strings. This is more efficient because python doesn't have to compile the regex pattern internally each time.

The following detail regex object methods. Most of them have the same syntax as Regex Functions, but some are more flexible with optional parameters.

Regex Object Methods

search

RegexObj.search(text)
re.compile(regexStr).search(text) is equivalent to re.search(regexStr, text). [see re.search]
RegexObj.search(text, startPos)
Match on substring starting at startPos.
RegexObj.search(text, startPos, endPos)
End at endPos.

The following have the same result:

match

RegexObj.match(text)
Same result as re.match(regexStr, text). [see re.match]
RegexObj.match(text, startPos)
Match on substring starting at startPos.
RegexObj.match(text, startPos, endPos)
End at endPos

split

RegexObj.split(text, …)
Same result as re.split(regexStr, text, …). [see re.split]

findall

RegexObj.findall(text)
Same result as re.findall(regexStr, text)
[see re.findall]
RegexObj.findall(text, startPos)
Match on substring starting at startPos.
RegexObj.findall(text, startPos, endPos)
End at endPos.

finditer

RegexObj.finditer(text)
Same result as re.finditer(regexStr, text)
[see re.finditer]
RegexObj.finditer(text, startPos)
Match on substring starting at startPos.
RegexObj.finditer(text, startPos, endPos)
End at endPos.

sub

RegexObj.sub( repl, text, …)
Same result as re.sub(regexStr, text, …).
[see re.sub]

subn

RegexObj.subn( repl, text, …)
Same result as re.subn(regexStr, text, …)
[see re.subn]

Regex Attributes

The following are constants assigned by the module when a pattern object is compiled.

.flags

RegexObj.flags
The flags argument used when the regex object was compiled, or 0 if no flags were provided. 
import re
patObj = re.compile(ur'\w', re.M|re.U)
print patObj.flags  # prints 40

.groupindex

RegexObj.groupindex
Return a dictionary. The keys are the named capture groups, the values are their order in the pattern. For example, here's a pattern of named group (?P<id>). The dictionary is empty if no symbolic groups were used in the pattern. 
# -*- coding: utf-8 -*-
# python 2

# example of regex .groupindex

import re

# a typical image tag
# <img src="cat.jpg" alt="cat" width="123" height="456">

# a pattern to capture image tag, with named group
xx = re.compile(r'src="(?P<filename>[^"]+)" alt="(?P<alttext>[^"]+)" width="(?P<width>\d+)" height="(?P<height>\d+)"')

print xx.groupindex #  {'height': 4, 'width': 3, 'alttext': 2, 'filename': 1}

.pattern

RegexObj.pattern
The pattern string from which the regex object was compiled.

Python Regular Expression