The simplest use of the re module is to determine whether a specified substring can be found in a string. Here is an example:

import re

substring = 'Hospital'
search = re.search(substring,'XYZ Hospital and Treatment Center')
if search:
    index = search.start()
    print "matched", substring, "at index", index
else:
    print "No match found"

This simple search is a two-step process. The first step is to call the re.search() function to perform the search. In this example, re.search() searches for the substring Hospital in the string XYZ Hospital and Treatment Center.

The value returned by re.search() depends on whether the search substring is found in the string:

• If the substring is found, re.search() returns a special object containing information about the matched substring.
• If the substring is not found, re.search() returns false.

The second step is to call start() to determine the index of the substring in the string. Like all indexes in Python, this index starts from 0; in start(), the index indicates how many characters were skipped before the substring was found. In this example, start() returns 4, which indicates that the matched substring was found after four characters were skipped.

	You cannot call start() if no match has been found. If you attempt to do this, Python generates a runtime error.