Beginning Python - From Novice to Professional

CHAPTER 10 ■ BATTERIES INCLUDED 239
Table 10-8. Some Important Functions in the re Module
Function
compile(pattern[, flags])
search(pattern, string[, flags])
match(pattern, string[, flags])
split(pattern, string[, maxsplit=0])
findall(pattern, string)
sub(pat, repl, string[, count=0])
escape(string)
Description
Creates a pattern object from a string with
a regexp
Searches for pattern in string
Matches pattern at the beginning of string
Splits a string by occurrences of pattern
Returns a list of all occurrences of pattern
in string
Substitutes occurrences of pat in string with repl
Escapes all special regexp characters in string
The function re.compile transforms a regular expression (written as a string) to a pattern
object, which can be used for more efficient matching. If you use regular expressions represented
as strings when you call functions such as search or match, they have to be transformed into
regular expression objects internally anyway. By doing this once, with the compile function,
this step is no longer necessary each time you use the pattern. The pattern objects have the
searching/matching functions as methods, so re.search(pat, string) (where pat is a regexp
written as a string) is equivalent to pat.search(string) (where pat is a pattern object created
with compile). Compiled regexp objects can also be used in the normal re functions.
The function re.search searches a given string to find the first substring, if any, that matches
the given regular expression. If one is found, a MatchObject (evaluating to true) is returned;
otherwise None (evaluating to false) is returned. Due to the nature of the return values, the function
can be used in conditional statements, such as
if re.search(pat, string):
print 'Found it!'
However, if you need more information about the matched substring, you can examine
the returned MatchObject. (More about MatchObjects in the next section.)
The function re.match tries to match a regular expression at the beginning of a given string.
So match('p', 'python') returns true, while match('p', 'www.python.org') returns false. (The
return values are the same as those for search.)
■Note The match function will report a match if the pattern matches the beginning of a string; the
pattern is not required to match the entire string. If you want to do that, you have to add a dollar sign to the
end of your pattern; the dollar sign will match the end of the string and thereby “stretch out” the match.