3.1 Compiling Regular Expressions

Regular expressions are compiled into RegexObject instances, which then have methods for various operations such as searching for pattern matches or performing string substitutions.

>>> import re
>>> p = re.compile('ab*')
>>> print p
<re.RegexObject instance at 80b4150>

re.compile() also accepts an optional flags argument, used to enable various special features and syntax variations. We'll go over the available settings later, but for now a single example will do:

>>> p = re.compile('ab*', re.IGNORECASE)

The RE is passed to re.compile() as a string. REs are handled as strings because regular expressions aren't part of the core Python language, and no special syntax was created for expressing them. (There are applications that don't need REs at all, so there's no need to bloat the language specification by including them.) Instead, the re module is just a C extension module, just like the string module.

Putting REs in strings keeps the Python language simpler, but has one disadvantage which is the topic of the next section.