6.6. String Built-in Methods

String methods were recently added to Python, introduced in version 1.6 (and in JPython 1.1), and tweaked for 2.0. These methods are intended to replace most of the functionality in the string module as well as to bring new functionality to the table. Table 6.6 shows all the current methods for strings. All string methods should fully support Unicode strings. And some are applicable only to Unicode strings.

Table 6.6. String Type Built-in Methods
ValueDescription
string.capitalize()capitalizes first letter of string
string.center(width)returns a space-padded string with the original string centered to a total of width columns
string.count(str, beg= 0,end=len(string))counts how many times str occurs in string, or in a substring of string if starting index beg and ending index end are given
string.encode(encoding='UTF-8', errors='strict')[a]returns encoded string version of string; on error, default is to raise a ValueError unless errors is given with 'ignore' or 'replace'.
string.endswith(str, beg=0, end=len(string))[b]determines if string or a substring of string (if starting index beg and ending index end are given) ends with str; returns 1 if so, and 0 otherwise
string.expandtabs(tabsize=8)expands tabs in string to multiple spaces; defaults to 8 spaces per tab if tabsize not provided
string.find(str, beg=0 end=len(string))determine if str occurs in string, or in a substring of string if starting index beg and ending index end are given; returns index if found and -1 otherwise
string.index(str, beg=0, end=len(string))same as find(), but raises an exception if str not found
string.isa1num()[a][b][c]returns 1 if string has at least 1 character and all characters are alphanumeric and 0 otherwise
string.isalpha()[a][b][c]returns 1 if string has at least 1 character and all characters are alphabetic and 0 otherwise
string.isdecimal()[b][c][d]returns 1 if string contains only decimal digits and 0 otherwise
string.isdigit()[b][c]returns 1 if string contains only digits and 0 otherwise
string.islower()[b][c]returns 1 if string has at least 1 cased character and all cased characters are in lowercase and 0 otherwise
string.isnumeric()[b][c][d]returns 1 if string contains only numeric characters and 0 otherwise
string.isspace()[b][c]returns 1 if string contains only whitespace characters and 0 otherwise
string.istitle()[b][c]returns 1 if string is properly “titlecased” (see title()) and 0 otherwise
string.isupper()[b][c]returns 1 if string has at least one cased character and all cased characters are in uppercase and 0 otherwise
string.join(seq)merges (concatenates) the string representations of elements in sequence seq into a string, with separator string
string.ljust(width)returns a space-padded string with the original string left-justified to a total of width columns
string.lower()converts all uppercase letters in string to lowercase
string.lstrip()removes all leading whitespace in string
string.replace(str1, str2, num=string.count(str1))replaces all occurrences of str1 in string with str2, or at most num occurrences if num given
string.rfind(str, beg=0,end=len(string))same as find(), but search backwards in string
string.rindex( str, beg=0, end=len(string))same as index(), but search backwards in string
string.rjust(width)returns a space-padded string with the original string right-justified to a total of width columns.
string.rstrip()removes all trailing whitespace of string
string.split(str="", num=string.count(str))splits string according to delimiter str (space if not provided) and returns list of substrings; split into at most num substrings if given
string.splitlines( num=string.count(' '))[b][c]splits string at all (or num) NEWLINEs and returns a list of each line with NEWLINEs removed
string.startswith(str, beg=0,end=len(string))[b][c]determines if string or a substring of string (if starting index beg and ending index end are given) starts with substring str; returns 1 if so, and 0 otherwise
string.strip([obj])performs both lstrip() and rstrip() on string
string.swapcase()inverts case for all letters in string
string.title()[b][c]returns “titlecased” version of string, that is, all words begin with uppercase, and the rest are lowercase (also see istitle())
string.translate(str, del="")translates string according to translation table str(256 chars), removing those in the del string
string.upper()converts lowercase letters in string to uppercase
string.zfill (width)returns original string left-padded with zeros to a total of width characters; intended for numbers, zfill() retains any sign given (less one zero)

[a] applicable to Unicode strings only in 1.6, but to all string types in 2.0.

[b] not available as a string module function in 1.5.2

[c] not available as a method in JPython 1.1

[d] applicable to Unicode strings only

Using JPython, we will show some examples of methods available for strings:

>>> quest = 'what is your favorite color?'
>>> quest.capitalize()
'What is your favorite color?'
>>>
>>> quest.center(40)
'      what is your favorite color?      '
>>>
>>> quest.count('or')
2
>>>
>>> quest.endswith('blue')
0
>>>
>>> quest.endswith('color?')
1
>>>
>>> quest.find('or', 30)
-1
>>>
>>> quest.find('or', 22)
25
>>
>>> quest.index('or', 10)
16
>>>
>>> ':'.join(quest.split())
'what:is:your:favorite:color?'
>>> quest.replace('favorite color', 'quest')
>>>
'what is your quest?'
>>>
>>> quest.upper()
'WHAT IS YOUR FAVORITE COLOR?'

The most complex example shown above is the one with split() and join(). We first call split() on our string, which, without an argument, will break apart our string using spaces as the delimiter. We then take this list of words and call join() to merge our words again, but with a new delimiter, the colon. Notice that we used the split() method for our string, and the join() method for single-character string ':'.

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