Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 1 | \section{Standard Module \sectcode{string}} |
| 2 | |
| 3 | \stmodindex{string} |
| 4 | |
| 5 | This module defines some constants useful for checking character |
Guido van Rossum | 0bf4d89 | 1995-03-02 12:37:30 +0000 | [diff] [blame] | 6 | classes and some useful string functions. See the modules |
| 7 | \code{regex} and \code{regsub} for string functions based on regular |
| 8 | expressions. |
| 9 | |
| 10 | The constants defined in this module are are: |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 11 | |
| 12 | \renewcommand{\indexsubitem}{(data in module string)} |
| 13 | \begin{datadesc}{digits} |
| 14 | The string \code{'0123456789'}. |
| 15 | \end{datadesc} |
| 16 | |
| 17 | \begin{datadesc}{hexdigits} |
| 18 | The string \code{'0123456789abcdefABCDEF'}. |
| 19 | \end{datadesc} |
| 20 | |
| 21 | \begin{datadesc}{letters} |
| 22 | The concatenation of the strings \code{lowercase} and |
| 23 | \code{uppercase} described below. |
| 24 | \end{datadesc} |
| 25 | |
| 26 | \begin{datadesc}{lowercase} |
| 27 | A string containing all the characters that are considered lowercase |
| 28 | letters. On most systems this is the string |
Guido van Rossum | 8675115 | 1995-02-28 17:14:32 +0000 | [diff] [blame] | 29 | \code{'abcdefghijklmnopqrstuvwxyz'}. Do not change its definition --- |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 30 | the effect on the routines \code{upper} and \code{swapcase} is |
| 31 | undefined. |
| 32 | \end{datadesc} |
| 33 | |
| 34 | \begin{datadesc}{octdigits} |
| 35 | The string \code{'01234567'}. |
| 36 | \end{datadesc} |
| 37 | |
| 38 | \begin{datadesc}{uppercase} |
| 39 | A string containing all the characters that are considered uppercase |
| 40 | letters. On most systems this is the string |
Guido van Rossum | 8675115 | 1995-02-28 17:14:32 +0000 | [diff] [blame] | 41 | \code{'ABCDEFGHIJKLMNOPQRSTUVWXYZ'}. Do not change its definition --- |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 42 | the effect on the routines \code{lower} and \code{swapcase} is |
| 43 | undefined. |
| 44 | \end{datadesc} |
| 45 | |
| 46 | \begin{datadesc}{whitespace} |
| 47 | A string containing all characters that are considered whitespace. |
| 48 | On most systems this includes the characters space, tab, linefeed, |
Guido van Rossum | 8675115 | 1995-02-28 17:14:32 +0000 | [diff] [blame] | 49 | return, formfeed, and vertical tab. Do not change its definition --- |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 50 | the effect on the routines \code{strip} and \code{split} is |
| 51 | undefined. |
| 52 | \end{datadesc} |
| 53 | |
Guido van Rossum | 0bf4d89 | 1995-03-02 12:37:30 +0000 | [diff] [blame] | 54 | The functions defined in this module are: |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 55 | |
| 56 | \renewcommand{\indexsubitem}{(in module string)} |
| 57 | |
| 58 | \begin{funcdesc}{atof}{s} |
| 59 | Convert a string to a floating point number. The string must have |
| 60 | the standard syntax for a floating point literal in Python, optionally |
| 61 | preceded by a sign (\samp{+} or \samp{-}). |
| 62 | \end{funcdesc} |
| 63 | |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 64 | \begin{funcdesc}{atoi}{s\optional{\, base}} |
| 65 | Convert string \var{s} to an integer in the given \var{base}. The |
| 66 | string must consist of one or more digits, optionally preceded by a |
| 67 | sign (\samp{+} or \samp{-}). The \var{base} defaults to 10. If it is |
| 68 | 0, a default base is chosen depending on the leading characters of the |
| 69 | string (after stripping the sign): \samp{0x} or \samp{0X} means 16, |
| 70 | \samp{0} means 8, anything else means 10. If \var{base} is 16, a |
| 71 | leading \samp{0x} or \samp{0X} is always accepted. (Note: for a more |
| 72 | flexible interpretation of numeric literals, use the built-in function |
Guido van Rossum | 96628a9 | 1995-04-10 11:34:00 +0000 | [diff] [blame] | 73 | \code{eval()}.) |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 74 | \bifuncindex{eval} |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 75 | \end{funcdesc} |
| 76 | |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 77 | \begin{funcdesc}{atol}{s\optional{\, base}} |
| 78 | Convert string \var{s} to a long integer in the given \var{base}. The |
| 79 | string must consist of one or more digits, optionally preceded by a |
| 80 | sign (\samp{+} or \samp{-}). The \var{base} argument has the same |
| 81 | meaning as for \code{atoi()}. A trailing \samp{l} or \samp{L} is not |
Guido van Rossum | 264302d | 1996-02-12 23:20:12 +0000 | [diff] [blame] | 82 | allowed, except if the base is 0. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 83 | \end{funcdesc} |
| 84 | |
| 85 | \begin{funcdesc}{expandtabs}{s\, tabsize} |
Guido van Rossum | 6bb1adc | 1995-03-13 10:03:32 +0000 | [diff] [blame] | 86 | Expand tabs in a string, i.e.\ replace them by one or more spaces, |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 87 | depending on the current column and the given tab size. The column |
| 88 | number is reset to zero after each newline occurring in the string. |
| 89 | This doesn't understand other non-printing characters or escape |
| 90 | sequences. |
| 91 | \end{funcdesc} |
| 92 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 93 | \begin{funcdesc}{find}{s\, sub\optional{\, start}} |
| 94 | Return the lowest index in \var{s} not smaller than \var{start} where the |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 95 | substring \var{sub} is found. Return \code{-1} when \var{sub} |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 96 | does not occur as a substring of \var{s} with index at least \var{start}. |
| 97 | If \var{start} is omitted, it defaults to \code{0}. If \var{start} is |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 98 | negative, \code{len(\var{s})} is added. |
| 99 | \end{funcdesc} |
| 100 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 101 | \begin{funcdesc}{rfind}{s\, sub\optional{\, start}} |
Guido van Rossum | 6bb1adc | 1995-03-13 10:03:32 +0000 | [diff] [blame] | 102 | Like \code{find} but find the highest index. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 103 | \end{funcdesc} |
| 104 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 105 | \begin{funcdesc}{index}{s\, sub\optional{\, start}} |
Guido van Rossum | 2828e9d | 1994-08-17 13:16:34 +0000 | [diff] [blame] | 106 | Like \code{find} but raise \code{ValueError} when the substring is |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 107 | not found. |
| 108 | \end{funcdesc} |
| 109 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 110 | \begin{funcdesc}{rindex}{s\, sub\optional{\, start}} |
Guido van Rossum | 2828e9d | 1994-08-17 13:16:34 +0000 | [diff] [blame] | 111 | Like \code{rfind} but raise \code{ValueError} when the substring is |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 112 | not found. |
| 113 | \end{funcdesc} |
| 114 | |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 115 | \begin{funcdesc}{count}{s\, sub\optional{\, start}} |
Guido van Rossum | ab3a250 | 1994-08-01 12:18:36 +0000 | [diff] [blame] | 116 | Return the number of (non-overlapping) occurrences of substring |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 117 | \var{sub} in string \var{s} with index at least \var{start}. |
| 118 | If \var{start} is omitted, it defaults to \code{0}. If \var{start} is |
| 119 | negative, \code{len(\var{s})} is added. |
Guido van Rossum | ab3a250 | 1994-08-01 12:18:36 +0000 | [diff] [blame] | 120 | \end{funcdesc} |
| 121 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 122 | \begin{funcdesc}{lower}{s} |
| 123 | Convert letters to lower case. |
| 124 | \end{funcdesc} |
| 125 | |
Guido van Rossum | f4d0d57 | 1996-07-30 18:23:05 +0000 | [diff] [blame^] | 126 | \begin{funcdesc}{maketrans}{from, to} |
| 127 | Return a translation table suitable for passing to \code{string.translate} |
| 128 | or \code{regex.compile}, that will map each character in \var{from} |
| 129 | into the character at the same position in \var{to}; \var{from} and |
| 130 | \var{to} must have the same length. |
| 131 | \end{funcdesc} |
| 132 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 133 | \begin{funcdesc}{split}{s} |
Guido van Rossum | 6bb1adc | 1995-03-13 10:03:32 +0000 | [diff] [blame] | 134 | Return a list of the whitespace-delimited words of the string |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 135 | \var{s}. |
| 136 | \end{funcdesc} |
| 137 | |
| 138 | \begin{funcdesc}{splitfields}{s\, sep} |
Guido van Rossum | 6bb1adc | 1995-03-13 10:03:32 +0000 | [diff] [blame] | 139 | Return a list containing the fields of the string \var{s}, using |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 140 | the string \var{sep} as a separator. The list will have one more |
| 141 | items than the number of non-overlapping occurrences of the |
| 142 | separator in the string. Thus, \code{string.splitfields(\var{s}, ' |
| 143 | ')} is not the same as \code{string.split(\var{s})}, as the latter |
| 144 | only returns non-empty words. As a special case, |
| 145 | \code{splitfields(\var{s}, '')} returns \code{[\var{s}]}, for any string |
| 146 | \var{s}. (See also \code{regsub.split()}.) |
| 147 | \end{funcdesc} |
| 148 | |
| 149 | \begin{funcdesc}{join}{words} |
| 150 | Concatenate a list or tuple of words with intervening spaces. |
| 151 | \end{funcdesc} |
| 152 | |
| 153 | \begin{funcdesc}{joinfields}{words\, sep} |
| 154 | Concatenate a list or tuple of words with intervening separators. |
| 155 | It is always true that |
| 156 | \code{string.joinfields(string.splitfields(\var{t}, \var{sep}), \var{sep})} |
| 157 | equals \var{t}. |
| 158 | \end{funcdesc} |
| 159 | |
| 160 | \begin{funcdesc}{strip}{s} |
Guido van Rossum | 6bb1adc | 1995-03-13 10:03:32 +0000 | [diff] [blame] | 161 | Remove leading and trailing whitespace from the string |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 162 | \var{s}. |
| 163 | \end{funcdesc} |
| 164 | |
| 165 | \begin{funcdesc}{swapcase}{s} |
Guido van Rossum | 6bb1adc | 1995-03-13 10:03:32 +0000 | [diff] [blame] | 166 | Convert lower case letters to upper case and vice versa. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 167 | \end{funcdesc} |
| 168 | |
Guido van Rossum | f4d0d57 | 1996-07-30 18:23:05 +0000 | [diff] [blame^] | 169 | \begin{funcdesc}{translate}{s, table\optional{, deletechars}} |
| 170 | Delete all characters from \var{s} that are in \var{deletechars} (if present), and |
| 171 | then translate the characters using \var{table}, which must be |
Guido van Rossum | f65f278 | 1995-09-13 17:37:21 +0000 | [diff] [blame] | 172 | a 256-character string giving the translation for each character |
Guido van Rossum | f4d0d57 | 1996-07-30 18:23:05 +0000 | [diff] [blame^] | 173 | value, indexed by its ordinal. |
Guido van Rossum | f65f278 | 1995-09-13 17:37:21 +0000 | [diff] [blame] | 174 | \end{funcdesc} |
| 175 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 176 | \begin{funcdesc}{upper}{s} |
| 177 | Convert letters to upper case. |
| 178 | \end{funcdesc} |
| 179 | |
| 180 | \begin{funcdesc}{ljust}{s\, width} |
| 181 | \funcline{rjust}{s\, width} |
| 182 | \funcline{center}{s\, width} |
| 183 | These functions respectively left-justify, right-justify and center a |
| 184 | string in a field of given width. |
| 185 | They return a string that is at least |
| 186 | \var{width} |
| 187 | characters wide, created by padding the string |
| 188 | \var{s} |
| 189 | with spaces until the given width on the right, left or both sides. |
| 190 | The string is never truncated. |
| 191 | \end{funcdesc} |
| 192 | |
| 193 | \begin{funcdesc}{zfill}{s\, width} |
| 194 | Pad a numeric string on the left with zero digits until the given |
| 195 | width is reached. Strings starting with a sign are handled correctly. |
| 196 | \end{funcdesc} |
Guido van Rossum | 0bf4d89 | 1995-03-02 12:37:30 +0000 | [diff] [blame] | 197 | |
| 198 | This module is implemented in Python. Much of its functionality has |
| 199 | been reimplemented in the built-in module \code{strop}. However, you |
| 200 | should \emph{never} import the latter module directly. When |
| 201 | \code{string} discovers that \code{strop} exists, it transparently |
| 202 | replaces parts of itself with the implementation from \code{strop}. |
| 203 | After initialization, there is \emph{no} overhead in using |
| 204 | \code{string} instead of \code{strop}. |
| 205 | \bimodindex{strop} |