Python Standard Library

The string Module

The string module contains a number of functions to process standard Python strings, as shown in Example 1-51.

Example 1-51. Using the string Module

File: string-example-1.py

import string

text = "Monty Python's Flying Circus"

print "upper", "=>", string.upper(text)
print "lower", "=>", string.lower(text)
print "split", "=>", string.split(text)
print "join", "=>", string.join(string.split(text), "+")
print "replace", "=>", string.replace(text, "Python", "Java")
print "find", "=>", string.find(text, "Python"), string.find(text, "Java")
print "count", "=>", string.count(text, "n")

upper => MONTY PYTHON'S FLYING CIRCUS
lower => monty python's flying circus
split => ['Monty', "Python's", 'Flying', 'Circus']
join => Monty+Python's+Flying+Circus
replace => Monty Java's Flying Circus
find => 6 -1
count => 3

In Python 1.5.2 and earlier, the string module uses functions from the strop implementation module where possible.

In Python 1.6 and later, most string operations are made available as string methods as well, as shown in Example 1-52. Many of the functions in the string module are simply wrapper functions that call the corresponding string method.

Example 1-52. Using string Methods Instead of string Module Functions

File: string-example-2.py

text = "Monty Python's Flying Circus"

print "upper", "=>", text.upper()
print "lower", "=>", text.lower()
print "split", "=>", text.split()
print "join", "=>", "+".join(text.split())
print "replace", "=>", text.replace("Python", "Perl")
print "find", "=>", text.find("Python"), text.find("Perl")
print "count", "=>", text.count("n")

upper => MONTY PYTHON'S FLYING CIRCUS
lower => monty python's flying circus
split => ['Monty', "Python's", 'Flying', 'Circus']
join => Monty+Python's+Flying+Circus
replace => Monty Perl's Flying Circus
find => 6 -1
count => 3

In addition to the string-manipulation capabilities offered by string, the module also contains a number of functions that convert strings to other types (as Example 1-53 demonstrates).

Example 1-53. Using the string Module to Convert Strings to Numbers

File: string-example-3.py

import string

print int("4711"),
print string.atoi("4711"),
print string.atoi("11147", 8), # octal
print string.atoi("1267", 16), # hexadecimal
print string.atoi("3mv", 36) # whatever...

print string.atoi("4711", 0),
print string.atoi("04711", 0),
print string.atoi("0x4711", 0)

print float("4711"),
print string.atof("1"),
print string.atof("1.23e5")

4711 4711 4711 4711 4711
4711 2505 18193
4711.0 1.0 123000.0

In most cases (especially if you’re using 1.6 or later), you can use the int and float functions instead of their string module counterparts.

The atoi function takes an optional second argument, which specifices the number base. If the base is 0, the function looks at the first few characters before attempting to interpret the value: if “0x,” the base is set to 16 (hexadecimal), and if “0,” the base is set to 8 (octal). The default is base 10 (decimal), just as if you hadn’t provided an extra argument.

In 1.6 and later, int also accepts a second argument, just like atoi. Unlike the string versions, int and float accept Unicode strings.