Python Notes (0.14.0)

10. The string module

The string module provides additional tools to manipulate strings. Some methods available in the standard data tstructure are not available in the string module (e.g., isalpha).

10.1. Quick start

>>> string.digits

>>> string.punctuation

>>> string.lowercase
>>> string.letters
>>> string.uppercase

The following 3 function are equivalent to the previous 3 functions: string.ascii_letters, string.ascii_lowercase, string.ascii_uppercase

>>> string.expandtabs("a a\t",4)
'a a    '

>>> string.whitespace
'\t\n\x0b\x0c\r '

>>> string.octdigits

>>> string.hexdigits

string.printable() function is the concatenation of letterm digits and punctuation.

Capitalise each word of the sentence:

>>> string.capwords("this is a test")
'This Is A Test'

string.splitfields equivalent to the split method of a string string.joinfields equivalent to the join method of a string

There are deprecated functions atof, atoi, atol

>>> string.atof("2")

equivalent to

>> float("2")

You also have the atoi (cast to integer) and atol (cast to long)

A function of interest is string.maketrans. Can be used together with the translate method of the string data structure.

Return a translation table suitable for passing to translate(), that will map each character in from into the character at the same position in to; from and to must have the same length.

>>> t = string.maketrans("acgt", "tgca")
>>> "acgttgca".translate(t)

The Formatter class in the string module allows you to create and customize your own string formatting behaviors using the same implementation as the built-in format() method.

10.1.1. string.Formatter

Templates provide simpler string substitutions as described in PEP 292. Instead of the normal %-based substitutions, Templates support $-based substitutions, using the following rules:

10.1.2. string.Template

>>> from string import Template
>>> s = Template('$who likes $what')
>>> s.substitute(who='tim', what='kung pao')
'tim likes kung pao'
>>> d = dict(who='tim')
>>> Template('Give $who $100').substitute(d)
Traceback (most recent call last):
ValueError: Invalid placeholder in string: line 1, col 11
>>> Template('$who likes $what').substitute(d)
Traceback (most recent call last):
KeyError: 'what'
>>> Template('$who likes $what').safe_substitute(d)
'tim likes $what'