Delving Deeper

Regular Expressions

Finding Patterns in Text

The most common use for re is to search for patterns in text. The search() function takes the pattern and text to scan, and returns a Match object when the pattern is found. If the pattern is not found, search() returns None.

Each Match object holds information about the nature of the match, including the original input string, the regular expression used, and the location within the original string where the pattern occurs.

# re_simple_match.py

import re

pattern = 'this'
text = 'Does this text match the pattern?'

match = re.search(pattern, text)

s = match.start()
e = match.end()

print('Found "{}"\nin "{}"\nfrom {} to {} ("{}")'.format(
    match.re.pattern, match.string, s, e, text[s:e]))
import re
pattern = 'this'
text = 'Does this text match the pattern?'
match = re.search(pattern, text)
s = match.start()
e = match.end()
print('Found "{}"\nin "{}"\nfrom {} to {} ("{}")'.format(
 match.re.pattern, match.string, s, e, text[s:e]))

The start() and end() methods give the indexes into the string showing where the text matched by the pattern occurs.

$ python3 re_simple_match.py

Found "this"
in "Does this text match the pattern?"
from 5 to 9 ("this")