Fred Drake | 295da24 | 1998-08-10 19:42:37 +0000 | [diff] [blame] | 1 | \section{\module{string} --- |
Fred Drake | ffbe687 | 1999-04-22 21:23:22 +0000 | [diff] [blame^] | 2 | Common string operations} |
Fred Drake | b91e934 | 1998-07-23 17:59:49 +0000 | [diff] [blame] | 3 | |
Fred Drake | ffbe687 | 1999-04-22 21:23:22 +0000 | [diff] [blame^] | 4 | \declaremodule{standard}{string} |
Fred Drake | b91e934 | 1998-07-23 17:59:49 +0000 | [diff] [blame] | 5 | \modulesynopsis{Common string operations.} |
| 6 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 7 | |
| 8 | This module defines some constants useful for checking character |
Fred Drake | 6d2bdb6 | 1997-12-16 04:04:25 +0000 | [diff] [blame] | 9 | classes and some useful string functions. See the module |
Fred Drake | ffbe687 | 1999-04-22 21:23:22 +0000 | [diff] [blame^] | 10 | \refmodule{re}\refstmodindex{re} for string functions based on regular |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 11 | expressions. |
Guido van Rossum | 0bf4d89 | 1995-03-02 12:37:30 +0000 | [diff] [blame] | 12 | |
| 13 | The constants defined in this module are are: |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 14 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 15 | \begin{datadesc}{digits} |
| 16 | The string \code{'0123456789'}. |
| 17 | \end{datadesc} |
| 18 | |
| 19 | \begin{datadesc}{hexdigits} |
| 20 | The string \code{'0123456789abcdefABCDEF'}. |
| 21 | \end{datadesc} |
| 22 | |
| 23 | \begin{datadesc}{letters} |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 24 | The concatenation of the strings \function{lowercase()} and |
| 25 | \function{uppercase()} described below. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 26 | \end{datadesc} |
| 27 | |
| 28 | \begin{datadesc}{lowercase} |
| 29 | A string containing all the characters that are considered lowercase |
| 30 | letters. On most systems this is the string |
Guido van Rossum | 8675115 | 1995-02-28 17:14:32 +0000 | [diff] [blame] | 31 | \code{'abcdefghijklmnopqrstuvwxyz'}. Do not change its definition --- |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 32 | the effect on the routines \function{upper()} and |
| 33 | \function{swapcase()} is undefined. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 34 | \end{datadesc} |
| 35 | |
| 36 | \begin{datadesc}{octdigits} |
| 37 | The string \code{'01234567'}. |
| 38 | \end{datadesc} |
| 39 | |
| 40 | \begin{datadesc}{uppercase} |
| 41 | A string containing all the characters that are considered uppercase |
| 42 | letters. On most systems this is the string |
Guido van Rossum | 8675115 | 1995-02-28 17:14:32 +0000 | [diff] [blame] | 43 | \code{'ABCDEFGHIJKLMNOPQRSTUVWXYZ'}. Do not change its definition --- |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 44 | the effect on the routines \function{lower()} and |
| 45 | \function{swapcase()} is undefined. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 46 | \end{datadesc} |
| 47 | |
| 48 | \begin{datadesc}{whitespace} |
| 49 | A string containing all characters that are considered whitespace. |
| 50 | On most systems this includes the characters space, tab, linefeed, |
Guido van Rossum | 8675115 | 1995-02-28 17:14:32 +0000 | [diff] [blame] | 51 | return, formfeed, and vertical tab. Do not change its definition --- |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 52 | the effect on the routines \function{strip()} and \function{split()} |
| 53 | is undefined. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 54 | \end{datadesc} |
| 55 | |
Guido van Rossum | 0bf4d89 | 1995-03-02 12:37:30 +0000 | [diff] [blame] | 56 | The functions defined in this module are: |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 57 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 58 | |
| 59 | \begin{funcdesc}{atof}{s} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 60 | Convert a string to a floating point number. The string must have |
| 61 | the standard syntax for a floating point literal in Python, |
Fred Drake | 70a66c9 | 1999-02-18 16:08:36 +0000 | [diff] [blame] | 62 | optionally preceded by a sign (\samp{+} or \samp{-}). Note that |
| 63 | this behaves identical to the built-in function |
| 64 | \function{float()}\bifuncindex{float} when passed a string. |
| 65 | |
| 66 | \strong{Note:} When passing in a string, values for NaN\index{NaN} |
| 67 | and Infinity\index{Infinity} may be returned, depending on the |
| 68 | underlying C library. The specific set of strings accepted which |
| 69 | cause these values to be returned depends entirely on the C library |
| 70 | and is known to vary. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 71 | \end{funcdesc} |
| 72 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 73 | \begin{funcdesc}{atoi}{s\optional{, base}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 74 | Convert string \var{s} to an integer in the given \var{base}. The |
| 75 | string must consist of one or more digits, optionally preceded by a |
| 76 | sign (\samp{+} or \samp{-}). The \var{base} defaults to 10. If it |
| 77 | is 0, a default base is chosen depending on the leading characters |
| 78 | of the string (after stripping the sign): \samp{0x} or \samp{0X} |
| 79 | means 16, \samp{0} means 8, anything else means 10. If \var{base} |
| 80 | is 16, a leading \samp{0x} or \samp{0X} is always accepted. Note |
| 81 | that when invoked without \var{base} or with \var{base} set to 10, |
| 82 | this behaves identical to the built-in function \function{int()} |
| 83 | when passed a string. (Also note: for a more flexible |
| 84 | interpretation of numeric literals, use the built-in function |
| 85 | \function{eval()}\bifuncindex{eval}.) |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 86 | \end{funcdesc} |
| 87 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 88 | \begin{funcdesc}{atol}{s\optional{, base}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 89 | Convert string \var{s} to a long integer in the given \var{base}. |
| 90 | The string must consist of one or more digits, optionally preceded |
| 91 | by a sign (\samp{+} or \samp{-}). The \var{base} argument has the |
| 92 | same meaning as for \function{atoi()}. A trailing \samp{l} or |
| 93 | \samp{L} is not allowed, except if the base is 0. Note that when |
| 94 | invoked without \var{base} or with \var{base} set to 10, this |
| 95 | behaves identical to the built-in function |
| 96 | \function{long()}\bifuncindex{long} when passed a string. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 97 | \end{funcdesc} |
| 98 | |
Guido van Rossum | e5e55d7 | 1996-08-09 21:44:51 +0000 | [diff] [blame] | 99 | \begin{funcdesc}{capitalize}{word} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 100 | Capitalize the first character of the argument. |
Guido van Rossum | e5e55d7 | 1996-08-09 21:44:51 +0000 | [diff] [blame] | 101 | \end{funcdesc} |
| 102 | |
| 103 | \begin{funcdesc}{capwords}{s} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 104 | Split the argument into words using \function{split()}, capitalize |
| 105 | each word using \function{capitalize()}, and join the capitalized |
| 106 | words using \function{join()}. Note that this replaces runs of |
| 107 | whitespace characters by a single space, and removes leading and |
| 108 | trailing whitespace. |
Guido van Rossum | e5e55d7 | 1996-08-09 21:44:51 +0000 | [diff] [blame] | 109 | \end{funcdesc} |
| 110 | |
Guido van Rossum | 9700e9b | 1999-01-25 22:31:53 +0000 | [diff] [blame] | 111 | \begin{funcdesc}{expandtabs}{s, \optional{tabsize}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 112 | Expand tabs in a string, i.e.\ replace them by one or more spaces, |
| 113 | depending on the current column and the given tab size. The column |
| 114 | number is reset to zero after each newline occurring in the string. |
| 115 | This doesn't understand other non-printing characters or escape |
Guido van Rossum | 9700e9b | 1999-01-25 22:31:53 +0000 | [diff] [blame] | 116 | sequences. The tab size defaults to 8. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 117 | \end{funcdesc} |
| 118 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 119 | \begin{funcdesc}{find}{s, sub\optional{, start\optional{,end}}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 120 | Return the lowest index in \var{s} where the substring \var{sub} is |
| 121 | found such that \var{sub} is wholly contained in |
| 122 | \code{\var{s}[\var{start}:\var{end}]}. Return \code{-1} on failure. |
| 123 | Defaults for \var{start} and \var{end} and interpretation of |
| 124 | negative values is the same as for slices. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 125 | \end{funcdesc} |
| 126 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 127 | \begin{funcdesc}{rfind}{s, sub\optional{, start\optional{, end}}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 128 | Like \function{find()} but find the highest index. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 129 | \end{funcdesc} |
| 130 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 131 | \begin{funcdesc}{index}{s, sub\optional{, start\optional{, end}}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 132 | Like \function{find()} but raise \exception{ValueError} when the |
| 133 | substring is not found. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 134 | \end{funcdesc} |
| 135 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 136 | \begin{funcdesc}{rindex}{s, sub\optional{, start\optional{, end}}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 137 | Like \function{rfind()} but raise \exception{ValueError} when the |
| 138 | substring is not found. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 139 | \end{funcdesc} |
| 140 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 141 | \begin{funcdesc}{count}{s, sub\optional{, start\optional{, end}}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 142 | Return the number of (non-overlapping) occurrences of substring |
| 143 | \var{sub} in string \code{\var{s}[\var{start}:\var{end}]}. |
| 144 | Defaults for \var{start} and \var{end} and interpretation of |
| 145 | negative values is the same as for slices. |
Guido van Rossum | ab3a250 | 1994-08-01 12:18:36 +0000 | [diff] [blame] | 146 | \end{funcdesc} |
| 147 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 148 | \begin{funcdesc}{lower}{s} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 149 | Return a copy of \var{s}, but with upper case letters converted to |
| 150 | lower case. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 151 | \end{funcdesc} |
| 152 | |
Guido van Rossum | f4d0d57 | 1996-07-30 18:23:05 +0000 | [diff] [blame] | 153 | \begin{funcdesc}{maketrans}{from, to} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 154 | Return a translation table suitable for passing to |
| 155 | \function{translate()} or \function{regex.compile()}, that will map |
| 156 | each character in \var{from} into the character at the same position |
| 157 | in \var{to}; \var{from} and \var{to} must have the same length. |
Guido van Rossum | a3eebe6 | 1998-06-11 16:03:30 +0000 | [diff] [blame] | 158 | |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 159 | \strong{Warning:} don't use strings derived from \code{lowercase} |
| 160 | and \code{uppercase} as arguments; in some locales, these don't have |
| 161 | the same length. For case conversions, always use |
| 162 | \function{lower()} and \function{upper()}. |
Guido van Rossum | f4d0d57 | 1996-07-30 18:23:05 +0000 | [diff] [blame] | 163 | \end{funcdesc} |
| 164 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 165 | \begin{funcdesc}{split}{s\optional{, sep\optional{, maxsplit}}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 166 | Return a list of the words of the string \var{s}. If the optional |
| 167 | second argument \var{sep} is absent or \code{None}, the words are |
| 168 | separated by arbitrary strings of whitespace characters (space, tab, |
| 169 | newline, return, formfeed). If the second argument \var{sep} is |
| 170 | present and not \code{None}, it specifies a string to be used as the |
| 171 | word separator. The returned list will then have one more items |
| 172 | than the number of non-overlapping occurrences of the separator in |
| 173 | the string. The optional third argument \var{maxsplit} defaults to |
| 174 | 0. If it is nonzero, at most \var{maxsplit} number of splits occur, |
| 175 | and the remainder of the string is returned as the final element of |
| 176 | the list (thus, the list will have at most \code{\var{maxsplit}+1} |
| 177 | elements). |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 178 | \end{funcdesc} |
| 179 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 180 | \begin{funcdesc}{splitfields}{s\optional{, sep\optional{, maxsplit}}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 181 | This function behaves identically to \function{split()}. (In the |
| 182 | past, \function{split()} was only used with one argument, while |
| 183 | \function{splitfields()} was only used with two arguments.) |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 184 | \end{funcdesc} |
| 185 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 186 | \begin{funcdesc}{join}{words\optional{, sep}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 187 | Concatenate a list or tuple of words with intervening occurrences of |
| 188 | \var{sep}. The default value for \var{sep} is a single space |
| 189 | character. It is always true that |
| 190 | \samp{string.join(string.split(\var{s}, \var{sep}), \var{sep})} |
| 191 | equals \var{s}. |
Guido van Rossum | e5e55d7 | 1996-08-09 21:44:51 +0000 | [diff] [blame] | 192 | \end{funcdesc} |
| 193 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 194 | \begin{funcdesc}{joinfields}{words\optional{, sep}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 195 | This function behaves identical to \function{join()}. (In the past, |
| 196 | \function{join()} was only used with one argument, while |
| 197 | \function{joinfields()} was only used with two arguments.) |
Guido van Rossum | e5e55d7 | 1996-08-09 21:44:51 +0000 | [diff] [blame] | 198 | \end{funcdesc} |
| 199 | |
| 200 | \begin{funcdesc}{lstrip}{s} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 201 | Return a copy of \var{s} but without leading whitespace characters. |
Guido van Rossum | e5e55d7 | 1996-08-09 21:44:51 +0000 | [diff] [blame] | 202 | \end{funcdesc} |
| 203 | |
| 204 | \begin{funcdesc}{rstrip}{s} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 205 | Return a copy of \var{s} but without trailing whitespace |
| 206 | characters. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 207 | \end{funcdesc} |
| 208 | |
| 209 | \begin{funcdesc}{strip}{s} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 210 | Return a copy of \var{s} without leading or trailing whitespace. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 211 | \end{funcdesc} |
| 212 | |
| 213 | \begin{funcdesc}{swapcase}{s} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 214 | Return a copy of \var{s}, but with lower case letters |
| 215 | converted to upper case and vice versa. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 216 | \end{funcdesc} |
| 217 | |
Guido van Rossum | f4d0d57 | 1996-07-30 18:23:05 +0000 | [diff] [blame] | 218 | \begin{funcdesc}{translate}{s, table\optional{, deletechars}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 219 | Delete all characters from \var{s} that are in \var{deletechars} (if |
| 220 | present), and then translate the characters using \var{table}, which |
| 221 | must be a 256-character string giving the translation for each |
| 222 | character value, indexed by its ordinal. |
Guido van Rossum | f65f278 | 1995-09-13 17:37:21 +0000 | [diff] [blame] | 223 | \end{funcdesc} |
| 224 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 225 | \begin{funcdesc}{upper}{s} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 226 | Return a copy of \var{s}, but with lower case letters converted to |
| 227 | upper case. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 228 | \end{funcdesc} |
| 229 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 230 | \begin{funcdesc}{ljust}{s, width} |
| 231 | \funcline{rjust}{s, width} |
| 232 | \funcline{center}{s, width} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 233 | These functions respectively left-justify, right-justify and center |
| 234 | a string in a field of given width. They return a string that is at |
| 235 | least \var{width} characters wide, created by padding the string |
| 236 | \var{s} with spaces until the given width on the right, left or both |
| 237 | sides. The string is never truncated. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 238 | \end{funcdesc} |
| 239 | |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 240 | \begin{funcdesc}{zfill}{s, width} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 241 | Pad a numeric string on the left with zero digits until the given |
| 242 | width is reached. Strings starting with a sign are handled |
| 243 | correctly. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 244 | \end{funcdesc} |
Guido van Rossum | 0bf4d89 | 1995-03-02 12:37:30 +0000 | [diff] [blame] | 245 | |
Guido van Rossum | 740eb82 | 1997-04-02 05:56:16 +0000 | [diff] [blame] | 246 | \begin{funcdesc}{replace}{str, old, new\optional{, maxsplit}} |
Fred Drake | e848976 | 1998-12-21 18:56:13 +0000 | [diff] [blame] | 247 | Return a copy of string \var{str} with all occurrences of substring |
| 248 | \var{old} replaced by \var{new}. If the optional argument |
| 249 | \var{maxsplit} is given, the first \var{maxsplit} occurrences are |
| 250 | replaced. |
Guido van Rossum | c8a80cd | 1997-03-25 16:41:31 +0000 | [diff] [blame] | 251 | \end{funcdesc} |
| 252 | |
Guido van Rossum | 0bf4d89 | 1995-03-02 12:37:30 +0000 | [diff] [blame] | 253 | This module is implemented in Python. Much of its functionality has |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 254 | been reimplemented in the built-in module |
| 255 | \module{strop}\refbimodindex{strop}. However, you |
Guido van Rossum | 0bf4d89 | 1995-03-02 12:37:30 +0000 | [diff] [blame] | 256 | should \emph{never} import the latter module directly. When |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 257 | \module{string} discovers that \module{strop} exists, it transparently |
| 258 | replaces parts of itself with the implementation from \module{strop}. |
Guido van Rossum | 0bf4d89 | 1995-03-02 12:37:30 +0000 | [diff] [blame] | 259 | After initialization, there is \emph{no} overhead in using |
Fred Drake | cce1090 | 1998-03-17 06:33:25 +0000 | [diff] [blame] | 260 | \module{string} instead of \module{strop}. |