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<TITLE>string -- Python library reference</TITLE> Next: <A HREF="../r/regex" TYPE="Next">regex</A> Prev: <A HREF="../s/string_services" TYPE="Prev">String Services</A> Up: <A HREF="../s/string_services" TYPE="Up">String Services</A> Top: <A HREF="../t/top" TYPE="Top">Top</A> <H1>4.1. Standard Module <CODE>string</CODE></H1> This module defines some constants useful for checking character classes and some useful string functions. See the modules <CODE>regex</CODE> and <CODE>regsub</CODE> for string functions based on regular expressions. The constants defined in this module are are: <DL><DT>digits -- data of module string<DD> The string <CODE>'0123456789'</CODE>. </DL> <DL><DT>hexdigits -- data of module string<DD> The string <CODE>'0123456789abcdefABCDEF'</CODE>. </DL> <DL><DT>letters -- data of module string<DD> The concatenation of the strings <CODE>lowercase</CODE> and <CODE>uppercase</CODE> described below. </DL> <DL><DT>lowercase -- data of module string<DD> A string containing all the characters that are considered lowercase letters. On most systems this is the string <CODE>'abcdefghijklmnopqrstuvwxyz'</CODE>. Do not change its definition --- the effect on the routines <CODE>upper</CODE> and <CODE>swapcase</CODE> is undefined. </DL> <DL><DT>octdigits -- data of module string<DD> The string <CODE>'01234567'</CODE>. </DL> <DL><DT>uppercase -- data of module string<DD> A string containing all the characters that are considered uppercase letters. On most systems this is the string <CODE>'ABCDEFGHIJKLMNOPQRSTUVWXYZ'</CODE>. Do not change its definition --- the effect on the routines <CODE>lower</CODE> and <CODE>swapcase</CODE> is undefined. </DL> <DL><DT>whitespace -- data of module string<DD> A string containing all characters that are considered whitespace. On most systems this includes the characters space, tab, linefeed, return, formfeed, and vertical tab. Do not change its definition --- the effect on the routines <CODE>strip</CODE> and <CODE>split</CODE> is undefined. </DL> The functions defined in this module are: <DL><DT>atof (<VAR>s</VAR>) -- function of module string<DD> Convert a string to a floating point number. The string must have the standard syntax for a floating point literal in Python, optionally preceded by a sign (`<SAMP>+</SAMP>' or `<SAMP>-</SAMP>'). </DL> <DL><DT>atoi (<VAR>s</VAR>[, <VAR>base</VAR>]) -- function of module string<DD> Convert string <VAR>s</VAR> to an integer in the given <VAR>base</VAR>. The string must consist of one or more digits, optionally preceded by a sign (`<SAMP>+</SAMP>' or `<SAMP>-</SAMP>'). The <VAR>base</VAR> defaults to 10. If it is 0, a default base is chosen depending on the leading characters of the string (after stripping the sign): `<SAMP>0x</SAMP>' or `<SAMP>0X</SAMP>' means 16, `<SAMP>0</SAMP>' means 8, anything else means 10. If <VAR>base</VAR> is 16, a leading `<SAMP>0x</SAMP>' or `<SAMP>0X</SAMP>' is always accepted. (Note: for a more flexible interpretation of numeric literals, use the built-in function <CODE>eval()</CODE>.) </DL> <DL><DT>atol (<VAR>s</VAR>[, <VAR>base</VAR>]) -- function of module string<DD> Convert string <VAR>s</VAR> to a long integer in the given <VAR>base</VAR>. The string must consist of one or more digits, optionally preceded by a sign (`<SAMP>+</SAMP>' or `<SAMP>-</SAMP>'). The <VAR>base</VAR> argument has the same meaning as for <CODE>atoi()</CODE>. A trailing `<SAMP>l</SAMP>' or `<SAMP>L</SAMP>' is not allowed, except if the base is 0. </DL> <DL><DT>capitalize (<VAR>word</VAR>) -- function of module string<DD> Capitalize the first character of the argument. </DL> <DL><DT>capwords (<VAR>s</VAR>) -- function of module string<DD> Split the argument into words using <CODE>split</CODE>, capitalize each word using <CODE>capitalize</CODE>, and join the capitalized words using <CODE>join</CODE>. Note that this replaces runs of whitespace characters by a single space. (See also <CODE>regsub.capwords()</CODE> for a version that doesn't change the delimiters, and lets you specify a word separator.) </DL> <DL><DT>expandtabs (<VAR>s</VAR>, <VAR>tabsize</VAR>) -- function of module string<DD> Expand tabs in a string, i.e. replace them by one or more spaces, depending on the current column and the given tab size. The column number is reset to zero after each newline occurring in the string. This doesn't understand other non-printing characters or escape sequences. </DL> <DL><DT>find (<VAR>s</VAR>, <VAR>sub</VAR>[, <VAR>start</VAR>]) -- function of module string<DD> Return the lowest index in <VAR>s</VAR> not smaller than <VAR>start</VAR> where the substring <VAR>sub</VAR> is found. Return <CODE>-1</CODE> when <VAR>sub</VAR> does not occur as a substring of <VAR>s</VAR> with index at least <VAR>start</VAR>. If <VAR>start</VAR> is omitted, it defaults to <CODE>0</CODE>. If <VAR>start</VAR> is negative, <CODE>len(<VAR>s</VAR>)</CODE> is added. </DL> <DL><DT>rfind (<VAR>s</VAR>, <VAR>sub</VAR>[, <VAR>start</VAR>]) -- function of module string<DD> Like <CODE>find</CODE> but find the highest index. </DL> <DL><DT>index (<VAR>s</VAR>, <VAR>sub</VAR>[, <VAR>start</VAR>]) -- function of module string<DD> Like <CODE>find</CODE> but raise <CODE>ValueError</CODE> when the substring is not found. </DL> <DL><DT>rindex (<VAR>s</VAR>, <VAR>sub</VAR>[, <VAR>start</VAR>]) -- function of module string<DD> Like <CODE>rfind</CODE> but raise <CODE>ValueError</CODE> when the substring is not found. </DL> <DL><DT>count (<VAR>s</VAR>, <VAR>sub</VAR>[, <VAR>start</VAR>]) -- function of module string<DD> Return the number of (non-overlapping) occurrences of substring <VAR>sub</VAR> in string <VAR>s</VAR> with index at least <VAR>start</VAR>. If <VAR>start</VAR> is omitted, it defaults to <CODE>0</CODE>. If <VAR>start</VAR> is negative, <CODE>len(<VAR>s</VAR>)</CODE> is added. </DL> <DL><DT>lower (<VAR>s</VAR>) -- function of module string<DD> Convert letters to lower case. </DL> <DL><DT>maketrans (<VAR>from</VAR>, <VAR>to</VAR>) -- function of module string<DD> Return a translation table suitable for passing to <CODE>string.translate</CODE> or <CODE>regex.compile</CODE>, that will map each character in <VAR>from</VAR> into the character at the same position in <VAR>to</VAR>; <VAR>from</VAR> and <VAR>to</VAR> must have the same length. </DL> <DL><DT>split (<VAR>s</VAR>[, <VAR>sep</VAR>[, <VAR>maxsplit</VAR>]]) -- function of module string<DD> Return a list of the words of the string <VAR>s</VAR>. If the optional second argument <VAR>sep</VAR> is absent or <CODE>None</CODE>, the words are separated by arbitrary strings of whitespace characters (space, tab, newline, return, formfeed). If the second argument <VAR>sep</VAR> is present and not <CODE>None</CODE>, it specifies a string to be used as the word separator. The returned list will then have one more items than the number of non-overlapping occurrences of the separator in the string. The optional third argument <VAR>maxsplit</VAR> defaults to 0. If it is nonzero, at most <VAR>maxsplit</VAR> number of splits occur, and the remainder of the string is returned as the final element of the list (thus, the list will have at most <CODE><VAR>maxsplit</VAR>+1</CODE> elements). (See also <CODE>regsub.split()</CODE> for a version that allows specifying a regular expression as the separator.) </DL> <DL><DT>splitfields (<VAR>s</VAR>[, <VAR>sep</VAR>[, <VAR>maxsplit</VAR>]]) -- function of module string<DD> This function behaves identical to <CODE>split</CODE>. (In the past, <CODE>split</CODE> was only used with one argument, while <CODE>splitfields</CODE> was only used with two arguments.) </DL> <DL><DT>join (<VAR>words</VAR>[, <VAR>sep</VAR>]) -- function of module string<DD> Concatenate a list or tuple of words with intervening occurrences of <VAR>sep</VAR>. The default value for <VAR>sep</VAR> is a single space character. It is always true that <CODE>string.join(string.split(<VAR>s</VAR>, <VAR>sep</VAR>), <VAR>sep</VAR>)</CODE> equals <VAR>s</VAR>. </DL> <DL><DT>joinfields (<VAR>words</VAR>[, <VAR>sep</VAR>]) -- function of module string<DD> This function behaves identical to <CODE>join</CODE>. (In the past, <CODE>join</CODE> was only used with one argument, while <CODE>joinfields</CODE> was only used with two arguments.) </DL> <DL><DT>lstrip (<VAR>s</VAR>) -- function of module string<DD> Remove leading whitespace from the string <VAR>s</VAR>. </DL> <DL><DT>rstrip (<VAR>s</VAR>) -- function of module string<DD> Remove trailing whitespace from the string <VAR>s</VAR>. </DL> <DL><DT>strip (<VAR>s</VAR>) -- function of module string<DD> Remove leading and trailing whitespace from the string <VAR>s</VAR>. </DL> <DL><DT>swapcase (<VAR>s</VAR>) -- function of module string<DD> Convert lower case letters to upper case and vice versa. </DL> <DL><DT>translate (<VAR>s</VAR>, <VAR>table</VAR>[, <VAR>deletechars</VAR>]) -- function of module string<DD> Delete all characters from <VAR>s</VAR> that are in <VAR>deletechars</VAR> (if present), and then translate the characters using <VAR>table</VAR>, which must be a 256-character string giving the translation for each character value, indexed by its ordinal. </DL> <DL><DT>upper (<VAR>s</VAR>) -- function of module string<DD> Convert letters to upper case. </DL> <DL><DT>ljust (<VAR>s</VAR>, <VAR>width</VAR>) -- function of module string<DD> </DL> <DL><DT>rjust (<VAR>s</VAR>, <VAR>width</VAR>) -- function of module string<DD> </DL> <DL><DT>center (<VAR>s</VAR>, <VAR>width</VAR>) -- function of module string<DD> These functions respectively left-justify, right-justify and center a string in a field of given width. They return a string that is at least <VAR>width</VAR> characters wide, created by padding the string <VAR>s</VAR> with spaces until the given width on the right, left or both sides. The string is never truncated. </DL> <DL><DT>zfill (<VAR>s</VAR>, <VAR>width</VAR>) -- function of module string<DD> Pad a numeric string on the left with zero digits until the given width is reached. Strings starting with a sign are handled correctly. </DL> This module is implemented in Python. Much of its functionality has been reimplemented in the built-in module <CODE>strop</CODE>. However, you should never import the latter module directly. When <CODE>string</CODE> discovers that <CODE>strop</CODE> exists, it transparently replaces parts of itself with the implementation from <CODE>strop</CODE>. After initialization, there is no overhead in using <CODE>string</CODE> instead of <CODE>strop</CODE>.