Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1 | :mod:`re` --- Regular expression operations |
| 2 | =========================================== |
| 3 | |
| 4 | .. module:: re |
| 5 | :synopsis: Regular expression operations. |
| 6 | .. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com> |
| 7 | .. sectionauthor:: Andrew M. Kuchling <amk@amk.ca> |
| 8 | |
| 9 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 10 | This module provides regular expression matching operations similar to |
Georg Brandl | ed2a1db | 2009-06-08 07:48:27 +0000 | [diff] [blame] | 11 | those found in Perl. |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 12 | |
| 13 | Both patterns and strings to be searched can be Unicode strings as well as |
| 14 | 8-bit strings. However, Unicode strings and 8-bit strings cannot be mixed: |
| 15 | that is, you cannot match an Unicode string with a byte pattern or |
Georg Brandl | ae2dbe2 | 2009-03-13 19:04:40 +0000 | [diff] [blame] | 16 | vice-versa; similarly, when asking for a substitution, the replacement |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 17 | string must be of the same type as both the pattern and the search string. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 18 | |
| 19 | Regular expressions use the backslash character (``'\'``) to indicate |
| 20 | special forms or to allow special characters to be used without invoking |
| 21 | their special meaning. This collides with Python's usage of the same |
| 22 | character for the same purpose in string literals; for example, to match |
| 23 | a literal backslash, one might have to write ``'\\\\'`` as the pattern |
| 24 | string, because the regular expression must be ``\\``, and each |
| 25 | backslash must be expressed as ``\\`` inside a regular Python string |
| 26 | literal. |
| 27 | |
| 28 | The solution is to use Python's raw string notation for regular expression |
| 29 | patterns; backslashes are not handled in any special way in a string literal |
| 30 | prefixed with ``'r'``. So ``r"\n"`` is a two-character string containing |
| 31 | ``'\'`` and ``'n'``, while ``"\n"`` is a one-character string containing a |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 32 | newline. Usually patterns will be expressed in Python code using this raw |
| 33 | string notation. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 34 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 35 | It is important to note that most regular expression operations are available as |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 36 | module-level functions and methods on |
| 37 | :ref:`compiled regular expressions <re-objects>`. The functions are shortcuts |
| 38 | that don't require you to compile a regex object first, but miss some |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 39 | fine-tuning parameters. |
| 40 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 41 | .. seealso:: |
| 42 | |
| 43 | Mastering Regular Expressions |
| 44 | Book on regular expressions by Jeffrey Friedl, published by O'Reilly. The |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 45 | second edition of the book no longer covers Python at all, but the first |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 46 | edition covered writing good regular expression patterns in great detail. |
| 47 | |
| 48 | |
| 49 | .. _re-syntax: |
| 50 | |
| 51 | Regular Expression Syntax |
| 52 | ------------------------- |
| 53 | |
| 54 | A regular expression (or RE) specifies a set of strings that matches it; the |
| 55 | functions in this module let you check if a particular string matches a given |
| 56 | regular expression (or if a given regular expression matches a particular |
| 57 | string, which comes down to the same thing). |
| 58 | |
| 59 | Regular expressions can be concatenated to form new regular expressions; if *A* |
| 60 | and *B* are both regular expressions, then *AB* is also a regular expression. |
| 61 | In general, if a string *p* matches *A* and another string *q* matches *B*, the |
| 62 | string *pq* will match AB. This holds unless *A* or *B* contain low precedence |
| 63 | operations; boundary conditions between *A* and *B*; or have numbered group |
| 64 | references. Thus, complex expressions can easily be constructed from simpler |
| 65 | primitive expressions like the ones described here. For details of the theory |
| 66 | and implementation of regular expressions, consult the Friedl book referenced |
| 67 | above, or almost any textbook about compiler construction. |
| 68 | |
| 69 | A brief explanation of the format of regular expressions follows. For further |
Christian Heimes | 2202f87 | 2008-02-06 14:31:34 +0000 | [diff] [blame] | 70 | information and a gentler presentation, consult the :ref:`regex-howto`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 71 | |
| 72 | Regular expressions can contain both special and ordinary characters. Most |
| 73 | ordinary characters, like ``'A'``, ``'a'``, or ``'0'``, are the simplest regular |
| 74 | expressions; they simply match themselves. You can concatenate ordinary |
| 75 | characters, so ``last`` matches the string ``'last'``. (In the rest of this |
| 76 | section, we'll write RE's in ``this special style``, usually without quotes, and |
| 77 | strings to be matched ``'in single quotes'``.) |
| 78 | |
| 79 | Some characters, like ``'|'`` or ``'('``, are special. Special |
| 80 | characters either stand for classes of ordinary characters, or affect |
| 81 | how the regular expressions around them are interpreted. Regular |
| 82 | expression pattern strings may not contain null bytes, but can specify |
Raymond Hettinger | 5768e0c | 2011-10-19 14:10:07 -0700 | [diff] [blame] | 83 | the null byte using a ``\number`` notation such as ``'\x00'``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 84 | |
| 85 | |
| 86 | The special characters are: |
| 87 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 88 | ``'.'`` |
| 89 | (Dot.) In the default mode, this matches any character except a newline. If |
| 90 | the :const:`DOTALL` flag has been specified, this matches any character |
| 91 | including a newline. |
| 92 | |
| 93 | ``'^'`` |
| 94 | (Caret.) Matches the start of the string, and in :const:`MULTILINE` mode also |
| 95 | matches immediately after each newline. |
| 96 | |
| 97 | ``'$'`` |
| 98 | Matches the end of the string or just before the newline at the end of the |
| 99 | string, and in :const:`MULTILINE` mode also matches before a newline. ``foo`` |
| 100 | matches both 'foo' and 'foobar', while the regular expression ``foo$`` matches |
| 101 | only 'foo'. More interestingly, searching for ``foo.$`` in ``'foo1\nfoo2\n'`` |
Christian Heimes | 25bb783 | 2008-01-11 16:17:00 +0000 | [diff] [blame] | 102 | matches 'foo2' normally, but 'foo1' in :const:`MULTILINE` mode; searching for |
| 103 | a single ``$`` in ``'foo\n'`` will find two (empty) matches: one just before |
| 104 | the newline, and one at the end of the string. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 105 | |
| 106 | ``'*'`` |
| 107 | Causes the resulting RE to match 0 or more repetitions of the preceding RE, as |
| 108 | many repetitions as are possible. ``ab*`` will match 'a', 'ab', or 'a' followed |
| 109 | by any number of 'b's. |
| 110 | |
| 111 | ``'+'`` |
| 112 | Causes the resulting RE to match 1 or more repetitions of the preceding RE. |
| 113 | ``ab+`` will match 'a' followed by any non-zero number of 'b's; it will not |
| 114 | match just 'a'. |
| 115 | |
| 116 | ``'?'`` |
| 117 | Causes the resulting RE to match 0 or 1 repetitions of the preceding RE. |
| 118 | ``ab?`` will match either 'a' or 'ab'. |
| 119 | |
| 120 | ``*?``, ``+?``, ``??`` |
| 121 | The ``'*'``, ``'+'``, and ``'?'`` qualifiers are all :dfn:`greedy`; they match |
| 122 | as much text as possible. Sometimes this behaviour isn't desired; if the RE |
| 123 | ``<.*>`` is matched against ``'<H1>title</H1>'``, it will match the entire |
| 124 | string, and not just ``'<H1>'``. Adding ``'?'`` after the qualifier makes it |
| 125 | perform the match in :dfn:`non-greedy` or :dfn:`minimal` fashion; as *few* |
| 126 | characters as possible will be matched. Using ``.*?`` in the previous |
| 127 | expression will match only ``'<H1>'``. |
| 128 | |
| 129 | ``{m}`` |
| 130 | Specifies that exactly *m* copies of the previous RE should be matched; fewer |
| 131 | matches cause the entire RE not to match. For example, ``a{6}`` will match |
| 132 | exactly six ``'a'`` characters, but not five. |
| 133 | |
| 134 | ``{m,n}`` |
| 135 | Causes the resulting RE to match from *m* to *n* repetitions of the preceding |
| 136 | RE, attempting to match as many repetitions as possible. For example, |
| 137 | ``a{3,5}`` will match from 3 to 5 ``'a'`` characters. Omitting *m* specifies a |
| 138 | lower bound of zero, and omitting *n* specifies an infinite upper bound. As an |
| 139 | example, ``a{4,}b`` will match ``aaaab`` or a thousand ``'a'`` characters |
| 140 | followed by a ``b``, but not ``aaab``. The comma may not be omitted or the |
| 141 | modifier would be confused with the previously described form. |
| 142 | |
| 143 | ``{m,n}?`` |
| 144 | Causes the resulting RE to match from *m* to *n* repetitions of the preceding |
| 145 | RE, attempting to match as *few* repetitions as possible. This is the |
| 146 | non-greedy version of the previous qualifier. For example, on the |
| 147 | 6-character string ``'aaaaaa'``, ``a{3,5}`` will match 5 ``'a'`` characters, |
| 148 | while ``a{3,5}?`` will only match 3 characters. |
| 149 | |
| 150 | ``'\'`` |
| 151 | Either escapes special characters (permitting you to match characters like |
| 152 | ``'*'``, ``'?'``, and so forth), or signals a special sequence; special |
| 153 | sequences are discussed below. |
| 154 | |
| 155 | If you're not using a raw string to express the pattern, remember that Python |
| 156 | also uses the backslash as an escape sequence in string literals; if the escape |
| 157 | sequence isn't recognized by Python's parser, the backslash and subsequent |
| 158 | character are included in the resulting string. However, if Python would |
| 159 | recognize the resulting sequence, the backslash should be repeated twice. This |
| 160 | is complicated and hard to understand, so it's highly recommended that you use |
| 161 | raw strings for all but the simplest expressions. |
| 162 | |
| 163 | ``[]`` |
Ezio Melotti | 81231d9 | 2011-10-20 19:38:04 +0300 | [diff] [blame] | 164 | Used to indicate a set of characters. In a set: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 165 | |
Ezio Melotti | 81231d9 | 2011-10-20 19:38:04 +0300 | [diff] [blame] | 166 | * Characters can be listed individually, e.g. ``[amk]`` will match ``'a'``, |
| 167 | ``'m'``, or ``'k'``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 168 | |
Ezio Melotti | 81231d9 | 2011-10-20 19:38:04 +0300 | [diff] [blame] | 169 | * Ranges of characters can be indicated by giving two characters and separating |
| 170 | them by a ``'-'``, for example ``[a-z]`` will match any lowercase ASCII letter, |
| 171 | ``[0-5][0-9]`` will match all the two-digits numbers from ``00`` to ``59``, and |
| 172 | ``[0-9A-Fa-f]`` will match any hexadecimal digit. If ``-`` is escaped (e.g. |
| 173 | ``[a\-z]``) or if it's placed as the first or last character (e.g. ``[a-]``), |
| 174 | it will match a literal ``'-'``. |
| 175 | |
| 176 | * Special characters lose their special meaning inside sets. For example, |
| 177 | ``[(+*)]`` will match any of the literal characters ``'('``, ``'+'``, |
| 178 | ``'*'``, or ``')'``. |
| 179 | |
| 180 | * Character classes such as ``\w`` or ``\S`` (defined below) are also accepted |
| 181 | inside a set, although the characters they match depends on whether |
| 182 | :const:`ASCII` or :const:`LOCALE` mode is in force. |
| 183 | |
| 184 | * Characters that are not within a range can be matched by :dfn:`complementing` |
| 185 | the set. If the first character of the set is ``'^'``, all the characters |
| 186 | that are *not* in the set will be matched. For example, ``[^5]`` will match |
| 187 | any character except ``'5'``, and ``[^^]`` will match any character except |
| 188 | ``'^'``. ``^`` has no special meaning if it's not the first character in |
| 189 | the set. |
| 190 | |
| 191 | * To match a literal ``']'`` inside a set, precede it with a backslash, or |
| 192 | place it at the beginning of the set. For example, both ``[()[\]{}]`` and |
| 193 | ``[]()[{}]`` will both match a parenthesis. |
Mark Summerfield | 9e670c2 | 2008-05-31 13:05:34 +0000 | [diff] [blame] | 194 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 195 | ``'|'`` |
| 196 | ``A|B``, where A and B can be arbitrary REs, creates a regular expression that |
| 197 | will match either A or B. An arbitrary number of REs can be separated by the |
| 198 | ``'|'`` in this way. This can be used inside groups (see below) as well. As |
| 199 | the target string is scanned, REs separated by ``'|'`` are tried from left to |
| 200 | right. When one pattern completely matches, that branch is accepted. This means |
| 201 | that once ``A`` matches, ``B`` will not be tested further, even if it would |
| 202 | produce a longer overall match. In other words, the ``'|'`` operator is never |
| 203 | greedy. To match a literal ``'|'``, use ``\|``, or enclose it inside a |
| 204 | character class, as in ``[|]``. |
| 205 | |
| 206 | ``(...)`` |
| 207 | Matches whatever regular expression is inside the parentheses, and indicates the |
| 208 | start and end of a group; the contents of a group can be retrieved after a match |
| 209 | has been performed, and can be matched later in the string with the ``\number`` |
| 210 | special sequence, described below. To match the literals ``'('`` or ``')'``, |
| 211 | use ``\(`` or ``\)``, or enclose them inside a character class: ``[(] [)]``. |
| 212 | |
| 213 | ``(?...)`` |
| 214 | This is an extension notation (a ``'?'`` following a ``'('`` is not meaningful |
| 215 | otherwise). The first character after the ``'?'`` determines what the meaning |
| 216 | and further syntax of the construct is. Extensions usually do not create a new |
| 217 | group; ``(?P<name>...)`` is the only exception to this rule. Following are the |
| 218 | currently supported extensions. |
| 219 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 220 | ``(?aiLmsux)`` |
| 221 | (One or more letters from the set ``'a'``, ``'i'``, ``'L'``, ``'m'``, |
| 222 | ``'s'``, ``'u'``, ``'x'``.) The group matches the empty string; the |
Andrew M. Kuchling | 1c50e86 | 2009-06-01 00:11:36 +0000 | [diff] [blame] | 223 | letters set the corresponding flags: :const:`re.A` (ASCII-only matching), |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 224 | :const:`re.I` (ignore case), :const:`re.L` (locale dependent), |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 225 | :const:`re.M` (multi-line), :const:`re.S` (dot matches all), |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 226 | and :const:`re.X` (verbose), for the entire regular expression. (The |
| 227 | flags are described in :ref:`contents-of-module-re`.) This |
| 228 | is useful if you wish to include the flags as part of the regular |
| 229 | expression, instead of passing a *flag* argument to the |
Georg Brandl | f346ac0 | 2009-07-26 15:03:49 +0000 | [diff] [blame] | 230 | :func:`re.compile` function. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 231 | |
| 232 | Note that the ``(?x)`` flag changes how the expression is parsed. It should be |
| 233 | used first in the expression string, or after one or more whitespace characters. |
| 234 | If there are non-whitespace characters before the flag, the results are |
| 235 | undefined. |
| 236 | |
| 237 | ``(?:...)`` |
Georg Brandl | 3122ce3 | 2010-10-29 06:17:38 +0000 | [diff] [blame] | 238 | A non-capturing version of regular parentheses. Matches whatever regular |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 239 | expression is inside the parentheses, but the substring matched by the group |
| 240 | *cannot* be retrieved after performing a match or referenced later in the |
| 241 | pattern. |
| 242 | |
| 243 | ``(?P<name>...)`` |
| 244 | Similar to regular parentheses, but the substring matched by the group is |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 245 | accessible within the rest of the regular expression via the symbolic group |
| 246 | name *name*. Group names must be valid Python identifiers, and each group |
| 247 | name must be defined only once within a regular expression. A symbolic group |
| 248 | is also a numbered group, just as if the group were not named. So the group |
| 249 | named ``id`` in the example below can also be referenced as the numbered group |
| 250 | ``1``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 251 | |
| 252 | For example, if the pattern is ``(?P<id>[a-zA-Z_]\w*)``, the group can be |
| 253 | referenced by its name in arguments to methods of match objects, such as |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 254 | ``m.group('id')`` or ``m.end('id')``, and also by name in the regular |
| 255 | expression itself (using ``(?P=id)``) and replacement text given to |
| 256 | ``.sub()`` (using ``\g<id>``). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 257 | |
| 258 | ``(?P=name)`` |
| 259 | Matches whatever text was matched by the earlier group named *name*. |
| 260 | |
| 261 | ``(?#...)`` |
| 262 | A comment; the contents of the parentheses are simply ignored. |
| 263 | |
| 264 | ``(?=...)`` |
| 265 | Matches if ``...`` matches next, but doesn't consume any of the string. This is |
| 266 | called a lookahead assertion. For example, ``Isaac (?=Asimov)`` will match |
| 267 | ``'Isaac '`` only if it's followed by ``'Asimov'``. |
| 268 | |
| 269 | ``(?!...)`` |
| 270 | Matches if ``...`` doesn't match next. This is a negative lookahead assertion. |
| 271 | For example, ``Isaac (?!Asimov)`` will match ``'Isaac '`` only if it's *not* |
| 272 | followed by ``'Asimov'``. |
| 273 | |
| 274 | ``(?<=...)`` |
| 275 | Matches if the current position in the string is preceded by a match for ``...`` |
| 276 | that ends at the current position. This is called a :dfn:`positive lookbehind |
| 277 | assertion`. ``(?<=abc)def`` will find a match in ``abcdef``, since the |
| 278 | lookbehind will back up 3 characters and check if the contained pattern matches. |
| 279 | The contained pattern must only match strings of some fixed length, meaning that |
| 280 | ``abc`` or ``a|b`` are allowed, but ``a*`` and ``a{3,4}`` are not. Note that |
Ezio Melotti | 0a6b541 | 2012-04-29 07:34:46 +0300 | [diff] [blame] | 281 | patterns which start with positive lookbehind assertions will not match at the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 282 | beginning of the string being searched; you will most likely want to use the |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 283 | :func:`search` function rather than the :func:`match` function: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 284 | |
| 285 | >>> import re |
| 286 | >>> m = re.search('(?<=abc)def', 'abcdef') |
| 287 | >>> m.group(0) |
| 288 | 'def' |
| 289 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 290 | This example looks for a word following a hyphen: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 291 | |
| 292 | >>> m = re.search('(?<=-)\w+', 'spam-egg') |
| 293 | >>> m.group(0) |
| 294 | 'egg' |
| 295 | |
| 296 | ``(?<!...)`` |
| 297 | Matches if the current position in the string is not preceded by a match for |
| 298 | ``...``. This is called a :dfn:`negative lookbehind assertion`. Similar to |
| 299 | positive lookbehind assertions, the contained pattern must only match strings of |
| 300 | some fixed length. Patterns which start with negative lookbehind assertions may |
| 301 | match at the beginning of the string being searched. |
| 302 | |
| 303 | ``(?(id/name)yes-pattern|no-pattern)`` |
orsenthil@gmail.com | 476021b | 2011-03-12 10:46:25 +0800 | [diff] [blame] | 304 | Will try to match with ``yes-pattern`` if the group with given *id* or |
| 305 | *name* exists, and with ``no-pattern`` if it doesn't. ``no-pattern`` is |
| 306 | optional and can be omitted. For example, |
| 307 | ``(<)?(\w+@\w+(?:\.\w+)+)(?(1)>|$)`` is a poor email matching pattern, which |
| 308 | will match with ``'<user@host.com>'`` as well as ``'user@host.com'``, but |
| 309 | not with ``'<user@host.com'`` nor ``'user@host.com>'`` . |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 310 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 311 | |
| 312 | The special sequences consist of ``'\'`` and a character from the list below. |
| 313 | If the ordinary character is not on the list, then the resulting RE will match |
| 314 | the second character. For example, ``\$`` matches the character ``'$'``. |
| 315 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 316 | ``\number`` |
| 317 | Matches the contents of the group of the same number. Groups are numbered |
| 318 | starting from 1. For example, ``(.+) \1`` matches ``'the the'`` or ``'55 55'``, |
| 319 | but not ``'the end'`` (note the space after the group). This special sequence |
| 320 | can only be used to match one of the first 99 groups. If the first digit of |
| 321 | *number* is 0, or *number* is 3 octal digits long, it will not be interpreted as |
| 322 | a group match, but as the character with octal value *number*. Inside the |
| 323 | ``'['`` and ``']'`` of a character class, all numeric escapes are treated as |
| 324 | characters. |
| 325 | |
| 326 | ``\A`` |
| 327 | Matches only at the start of the string. |
| 328 | |
| 329 | ``\b`` |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 330 | Matches the empty string, but only at the beginning or end of a word. |
| 331 | A word is defined as a sequence of Unicode alphanumeric or underscore |
| 332 | characters, so the end of a word is indicated by whitespace or a |
Ezio Melotti | 5a045b9 | 2012-02-29 11:48:44 +0200 | [diff] [blame] | 333 | non-alphanumeric, non-underscore Unicode character. Note that formally, |
| 334 | ``\b`` is defined as the boundary between a ``\w`` and a ``\W`` character |
| 335 | (or vice versa), or between ``\w`` and the beginning/end of the string. |
| 336 | This means that ``r'\bfoo\b'`` matches ``'foo'``, ``'foo.'``, ``'(foo)'``, |
| 337 | ``'bar foo baz'`` but not ``'foobar'`` or ``'foo3'``. |
| 338 | |
| 339 | By default Unicode alphanumerics are the ones used, but this can be changed |
| 340 | by using the :const:`ASCII` flag. Inside a character range, ``\b`` |
| 341 | represents the backspace character, for compatibility with Python's string |
| 342 | literals. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 343 | |
| 344 | ``\B`` |
Ezio Melotti | 5a045b9 | 2012-02-29 11:48:44 +0200 | [diff] [blame] | 345 | Matches the empty string, but only when it is *not* at the beginning or end |
| 346 | of a word. This means that ``r'py\B'`` matches ``'python'``, ``'py3'``, |
| 347 | ``'py2'``, but not ``'py'``, ``'py.'``, or ``'py!'``. |
| 348 | ``\B`` is just the opposite of ``\b``, so word characters are |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 349 | Unicode alphanumerics or the underscore, although this can be changed |
| 350 | by using the :const:`ASCII` flag. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 351 | |
| 352 | ``\d`` |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 353 | For Unicode (str) patterns: |
Mark Dickinson | 1f26828 | 2009-07-28 17:22:36 +0000 | [diff] [blame] | 354 | Matches any Unicode decimal digit (that is, any character in |
| 355 | Unicode character category [Nd]). This includes ``[0-9]``, and |
| 356 | also many other digit characters. If the :const:`ASCII` flag is |
| 357 | used only ``[0-9]`` is matched (but the flag affects the entire |
| 358 | regular expression, so in such cases using an explicit ``[0-9]`` |
| 359 | may be a better choice). |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 360 | For 8-bit (bytes) patterns: |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 361 | Matches any decimal digit; this is equivalent to ``[0-9]``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 362 | |
| 363 | ``\D`` |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 364 | Matches any character which is not a Unicode decimal digit. This is |
| 365 | the opposite of ``\d``. If the :const:`ASCII` flag is used this |
| 366 | becomes the equivalent of ``[^0-9]`` (but the flag affects the entire |
| 367 | regular expression, so in such cases using an explicit ``[^0-9]`` may |
| 368 | be a better choice). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 369 | |
| 370 | ``\s`` |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 371 | For Unicode (str) patterns: |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 372 | Matches Unicode whitespace characters (which includes |
| 373 | ``[ \t\n\r\f\v]``, and also many other characters, for example the |
| 374 | non-breaking spaces mandated by typography rules in many |
| 375 | languages). If the :const:`ASCII` flag is used, only |
| 376 | ``[ \t\n\r\f\v]`` is matched (but the flag affects the entire |
| 377 | regular expression, so in such cases using an explicit |
| 378 | ``[ \t\n\r\f\v]`` may be a better choice). |
| 379 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 380 | For 8-bit (bytes) patterns: |
| 381 | Matches characters considered whitespace in the ASCII character set; |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 382 | this is equivalent to ``[ \t\n\r\f\v]``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 383 | |
| 384 | ``\S`` |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 385 | Matches any character which is not a Unicode whitespace character. This is |
| 386 | the opposite of ``\s``. If the :const:`ASCII` flag is used this |
| 387 | becomes the equivalent of ``[^ \t\n\r\f\v]`` (but the flag affects the entire |
| 388 | regular expression, so in such cases using an explicit ``[^ \t\n\r\f\v]`` may |
| 389 | be a better choice). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 390 | |
| 391 | ``\w`` |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 392 | For Unicode (str) patterns: |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 393 | Matches Unicode word characters; this includes most characters |
| 394 | that can be part of a word in any language, as well as numbers and |
| 395 | the underscore. If the :const:`ASCII` flag is used, only |
| 396 | ``[a-zA-Z0-9_]`` is matched (but the flag affects the entire |
| 397 | regular expression, so in such cases using an explicit |
| 398 | ``[a-zA-Z0-9_]`` may be a better choice). |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 399 | For 8-bit (bytes) patterns: |
| 400 | Matches characters considered alphanumeric in the ASCII character set; |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 401 | this is equivalent to ``[a-zA-Z0-9_]``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 402 | |
| 403 | ``\W`` |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 404 | Matches any character which is not a Unicode word character. This is |
| 405 | the opposite of ``\w``. If the :const:`ASCII` flag is used this |
| 406 | becomes the equivalent of ``[^a-zA-Z0-9_]`` (but the flag affects the |
| 407 | entire regular expression, so in such cases using an explicit |
| 408 | ``[^a-zA-Z0-9_]`` may be a better choice). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 409 | |
| 410 | ``\Z`` |
| 411 | Matches only at the end of the string. |
| 412 | |
| 413 | Most of the standard escapes supported by Python string literals are also |
| 414 | accepted by the regular expression parser:: |
| 415 | |
| 416 | \a \b \f \n |
Antoine Pitrou | 463badf | 2012-06-23 13:29:19 +0200 | [diff] [blame] | 417 | \r \t \u \U |
| 418 | \v \x \\ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 419 | |
Ezio Melotti | 285e51b | 2012-04-29 04:52:30 +0300 | [diff] [blame] | 420 | (Note that ``\b`` is used to represent word boundaries, and means "backspace" |
| 421 | only inside character classes.) |
| 422 | |
Antoine Pitrou | 463badf | 2012-06-23 13:29:19 +0200 | [diff] [blame] | 423 | ``'\u'`` and ``'\U'`` escape sequences are only recognized in Unicode |
| 424 | patterns. In bytes patterns they are not treated specially. |
| 425 | |
Raymond Hettinger | 5768e0c | 2011-10-19 14:10:07 -0700 | [diff] [blame] | 426 | Octal escapes are included in a limited form. If the first digit is a 0, or if |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 427 | there are three octal digits, it is considered an octal escape. Otherwise, it is |
| 428 | a group reference. As for string literals, octal escapes are always at most |
| 429 | three digits in length. |
| 430 | |
Antoine Pitrou | 463badf | 2012-06-23 13:29:19 +0200 | [diff] [blame] | 431 | .. versionchanged:: 3.3 |
| 432 | The ``'\u'`` and ``'\U'`` escape sequences have been added. |
| 433 | |
| 434 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 435 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 436 | .. _contents-of-module-re: |
| 437 | |
| 438 | Module Contents |
| 439 | --------------- |
| 440 | |
| 441 | The module defines several functions, constants, and an exception. Some of the |
| 442 | functions are simplified versions of the full featured methods for compiled |
| 443 | regular expressions. Most non-trivial applications always use the compiled |
| 444 | form. |
| 445 | |
| 446 | |
Georg Brandl | 1824415 | 2009-09-02 20:34:52 +0000 | [diff] [blame] | 447 | .. function:: compile(pattern, flags=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 448 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 449 | Compile a regular expression pattern into a regular expression object, which |
| 450 | can be used for matching using its :func:`match` and :func:`search` methods, |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 451 | described below. |
| 452 | |
| 453 | The expression's behaviour can be modified by specifying a *flags* value. |
| 454 | Values can be any of the following variables, combined using bitwise OR (the |
| 455 | ``|`` operator). |
| 456 | |
| 457 | The sequence :: |
| 458 | |
Gregory P. Smith | 4221c74 | 2009-03-02 05:04:04 +0000 | [diff] [blame] | 459 | prog = re.compile(pattern) |
| 460 | result = prog.match(string) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 461 | |
| 462 | is equivalent to :: |
| 463 | |
Gregory P. Smith | 4221c74 | 2009-03-02 05:04:04 +0000 | [diff] [blame] | 464 | result = re.match(pattern, string) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 465 | |
Georg Brandl | f346ac0 | 2009-07-26 15:03:49 +0000 | [diff] [blame] | 466 | but using :func:`re.compile` and saving the resulting regular expression |
| 467 | object for reuse is more efficient when the expression will be used several |
| 468 | times in a single program. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 469 | |
Gregory P. Smith | 4221c74 | 2009-03-02 05:04:04 +0000 | [diff] [blame] | 470 | .. note:: |
| 471 | |
| 472 | The compiled versions of the most recent patterns passed to |
| 473 | :func:`re.match`, :func:`re.search` or :func:`re.compile` are cached, so |
| 474 | programs that use only a few regular expressions at a time needn't worry |
| 475 | about compiling regular expressions. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 476 | |
| 477 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 478 | .. data:: A |
| 479 | ASCII |
| 480 | |
Georg Brandl | 4049ce0 | 2009-06-08 07:49:54 +0000 | [diff] [blame] | 481 | Make ``\w``, ``\W``, ``\b``, ``\B``, ``\d``, ``\D``, ``\s`` and ``\S`` |
| 482 | perform ASCII-only matching instead of full Unicode matching. This is only |
| 483 | meaningful for Unicode patterns, and is ignored for byte patterns. |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 484 | |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 485 | Note that for backward compatibility, the :const:`re.U` flag still |
| 486 | exists (as well as its synonym :const:`re.UNICODE` and its embedded |
Georg Brandl | ebeb44d | 2010-07-29 11:15:36 +0000 | [diff] [blame] | 487 | counterpart ``(?u)``), but these are redundant in Python 3 since |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 488 | matches are Unicode by default for strings (and Unicode matching |
| 489 | isn't allowed for bytes). |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 490 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 491 | |
Sandro Tosi | da785fd | 2012-01-01 12:55:20 +0100 | [diff] [blame] | 492 | .. data:: DEBUG |
| 493 | |
| 494 | Display debug information about compiled expression. |
| 495 | |
| 496 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 497 | .. data:: I |
| 498 | IGNORECASE |
| 499 | |
| 500 | Perform case-insensitive matching; expressions like ``[A-Z]`` will match |
Mark Summerfield | 8676534 | 2008-08-20 07:40:18 +0000 | [diff] [blame] | 501 | lowercase letters, too. This is not affected by the current locale |
| 502 | and works for Unicode characters as expected. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 503 | |
| 504 | |
| 505 | .. data:: L |
| 506 | LOCALE |
| 507 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 508 | Make ``\w``, ``\W``, ``\b``, ``\B``, ``\s`` and ``\S`` dependent on the |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 509 | current locale. The use of this flag is discouraged as the locale mechanism |
| 510 | is very unreliable, and it only handles one "culture" at a time anyway; |
Georg Brandl | ebeb44d | 2010-07-29 11:15:36 +0000 | [diff] [blame] | 511 | you should use Unicode matching instead, which is the default in Python 3 |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 512 | for Unicode (str) patterns. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 513 | |
| 514 | |
| 515 | .. data:: M |
| 516 | MULTILINE |
| 517 | |
| 518 | When specified, the pattern character ``'^'`` matches at the beginning of the |
| 519 | string and at the beginning of each line (immediately following each newline); |
| 520 | and the pattern character ``'$'`` matches at the end of the string and at the |
| 521 | end of each line (immediately preceding each newline). By default, ``'^'`` |
| 522 | matches only at the beginning of the string, and ``'$'`` only at the end of the |
| 523 | string and immediately before the newline (if any) at the end of the string. |
| 524 | |
| 525 | |
| 526 | .. data:: S |
| 527 | DOTALL |
| 528 | |
| 529 | Make the ``'.'`` special character match any character at all, including a |
| 530 | newline; without this flag, ``'.'`` will match anything *except* a newline. |
| 531 | |
| 532 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 533 | .. data:: X |
| 534 | VERBOSE |
| 535 | |
| 536 | This flag allows you to write regular expressions that look nicer. Whitespace |
| 537 | within the pattern is ignored, except when in a character class or preceded by |
| 538 | an unescaped backslash, and, when a line contains a ``'#'`` neither in a |
| 539 | character class or preceded by an unescaped backslash, all characters from the |
| 540 | leftmost such ``'#'`` through the end of the line are ignored. |
| 541 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 542 | That means that the two following regular expression objects that match a |
| 543 | decimal number are functionally equal:: |
Georg Brandl | 81ac1ce | 2007-08-31 17:17:17 +0000 | [diff] [blame] | 544 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 545 | a = re.compile(r"""\d + # the integral part |
| 546 | \. # the decimal point |
| 547 | \d * # some fractional digits""", re.X) |
| 548 | b = re.compile(r"\d+\.\d*") |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 549 | |
| 550 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 551 | |
| 552 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 553 | .. function:: search(pattern, string, flags=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 554 | |
| 555 | Scan through *string* looking for a location where the regular expression |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 556 | *pattern* produces a match, and return a corresponding :ref:`match object |
| 557 | <match-objects>`. Return ``None`` if no position in the string matches the |
| 558 | pattern; note that this is different from finding a zero-length match at some |
| 559 | point in the string. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 560 | |
| 561 | |
Georg Brandl | 1824415 | 2009-09-02 20:34:52 +0000 | [diff] [blame] | 562 | .. function:: match(pattern, string, flags=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 563 | |
| 564 | If zero or more characters at the beginning of *string* match the regular |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 565 | expression *pattern*, return a corresponding :ref:`match object |
| 566 | <match-objects>`. Return ``None`` if the string does not match the pattern; |
| 567 | note that this is different from a zero-length match. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 568 | |
Ezio Melotti | 443f000 | 2012-02-29 13:39:05 +0200 | [diff] [blame] | 569 | Note that even in :const:`MULTILINE` mode, :func:`re.match` will only match |
| 570 | at the beginning of the string and not at the beginning of each line. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 571 | |
Ezio Melotti | 443f000 | 2012-02-29 13:39:05 +0200 | [diff] [blame] | 572 | If you want to locate a match anywhere in *string*, use :func:`search` |
| 573 | instead (see also :ref:`search-vs-match`). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 574 | |
| 575 | |
Georg Brandl | 1824415 | 2009-09-02 20:34:52 +0000 | [diff] [blame] | 576 | .. function:: split(pattern, string, maxsplit=0, flags=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 577 | |
| 578 | Split *string* by the occurrences of *pattern*. If capturing parentheses are |
| 579 | used in *pattern*, then the text of all groups in the pattern are also returned |
| 580 | as part of the resulting list. If *maxsplit* is nonzero, at most *maxsplit* |
| 581 | splits occur, and the remainder of the string is returned as the final element |
Georg Brandl | 9647389 | 2008-03-06 07:09:43 +0000 | [diff] [blame] | 582 | of the list. :: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 583 | |
| 584 | >>> re.split('\W+', 'Words, words, words.') |
| 585 | ['Words', 'words', 'words', ''] |
| 586 | >>> re.split('(\W+)', 'Words, words, words.') |
| 587 | ['Words', ', ', 'words', ', ', 'words', '.', ''] |
| 588 | >>> re.split('\W+', 'Words, words, words.', 1) |
| 589 | ['Words', 'words, words.'] |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 590 | >>> re.split('[a-f]+', '0a3B9', flags=re.IGNORECASE) |
| 591 | ['0', '3', '9'] |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 592 | |
Christian Heimes | dd15f6c | 2008-03-16 00:07:10 +0000 | [diff] [blame] | 593 | If there are capturing groups in the separator and it matches at the start of |
| 594 | the string, the result will start with an empty string. The same holds for |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 595 | the end of the string: |
Christian Heimes | dd15f6c | 2008-03-16 00:07:10 +0000 | [diff] [blame] | 596 | |
| 597 | >>> re.split('(\W+)', '...words, words...') |
| 598 | ['', '...', 'words', ', ', 'words', '...', ''] |
| 599 | |
| 600 | That way, separator components are always found at the same relative |
Raymond Hettinger | 5768e0c | 2011-10-19 14:10:07 -0700 | [diff] [blame] | 601 | indices within the result list. |
Christian Heimes | dd15f6c | 2008-03-16 00:07:10 +0000 | [diff] [blame] | 602 | |
Thomas Wouters | 89d996e | 2007-09-08 17:39:28 +0000 | [diff] [blame] | 603 | Note that *split* will never split a string on an empty pattern match. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 604 | For example: |
Thomas Wouters | 89d996e | 2007-09-08 17:39:28 +0000 | [diff] [blame] | 605 | |
| 606 | >>> re.split('x*', 'foo') |
| 607 | ['foo'] |
| 608 | >>> re.split("(?m)^$", "foo\n\nbar\n") |
| 609 | ['foo\n\nbar\n'] |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 610 | |
Jeroen Ruigrok van der Werven | b70ccc3 | 2009-04-27 08:07:12 +0000 | [diff] [blame] | 611 | .. versionchanged:: 3.1 |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 612 | Added the optional flags argument. |
| 613 | |
Christian Heimes | dd15f6c | 2008-03-16 00:07:10 +0000 | [diff] [blame] | 614 | |
Georg Brandl | 1824415 | 2009-09-02 20:34:52 +0000 | [diff] [blame] | 615 | .. function:: findall(pattern, string, flags=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 616 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 617 | Return all non-overlapping matches of *pattern* in *string*, as a list of |
Georg Brandl | 3dbca81 | 2008-07-23 16:10:53 +0000 | [diff] [blame] | 618 | strings. The *string* is scanned left-to-right, and matches are returned in |
| 619 | the order found. If one or more groups are present in the pattern, return a |
| 620 | list of groups; this will be a list of tuples if the pattern has more than |
| 621 | one group. Empty matches are included in the result unless they touch the |
| 622 | beginning of another match. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 623 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 624 | |
Georg Brandl | 1824415 | 2009-09-02 20:34:52 +0000 | [diff] [blame] | 625 | .. function:: finditer(pattern, string, flags=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 626 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 627 | Return an :term:`iterator` yielding :ref:`match objects <match-objects>` over |
| 628 | all non-overlapping matches for the RE *pattern* in *string*. The *string* |
| 629 | is scanned left-to-right, and matches are returned in the order found. Empty |
Georg Brandl | 3dbca81 | 2008-07-23 16:10:53 +0000 | [diff] [blame] | 630 | matches are included in the result unless they touch the beginning of another |
| 631 | match. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 632 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 633 | |
Georg Brandl | 1824415 | 2009-09-02 20:34:52 +0000 | [diff] [blame] | 634 | .. function:: sub(pattern, repl, string, count=0, flags=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 635 | |
| 636 | Return the string obtained by replacing the leftmost non-overlapping occurrences |
| 637 | of *pattern* in *string* by the replacement *repl*. If the pattern isn't found, |
| 638 | *string* is returned unchanged. *repl* can be a string or a function; if it is |
| 639 | a string, any backslash escapes in it are processed. That is, ``\n`` is |
Sandro Tosi | 6a633bb | 2011-08-19 22:54:50 +0200 | [diff] [blame] | 640 | converted to a single newline character, ``\r`` is converted to a carriage return, and |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 641 | so forth. Unknown escapes such as ``\j`` are left alone. Backreferences, such |
| 642 | as ``\6``, are replaced with the substring matched by group 6 in the pattern. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 643 | For example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 644 | |
| 645 | >>> re.sub(r'def\s+([a-zA-Z_][a-zA-Z_0-9]*)\s*\(\s*\):', |
| 646 | ... r'static PyObject*\npy_\1(void)\n{', |
| 647 | ... 'def myfunc():') |
| 648 | 'static PyObject*\npy_myfunc(void)\n{' |
| 649 | |
| 650 | If *repl* is a function, it is called for every non-overlapping occurrence of |
| 651 | *pattern*. The function takes a single match object argument, and returns the |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 652 | replacement string. For example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 653 | |
| 654 | >>> def dashrepl(matchobj): |
| 655 | ... if matchobj.group(0) == '-': return ' ' |
| 656 | ... else: return '-' |
| 657 | >>> re.sub('-{1,2}', dashrepl, 'pro----gram-files') |
| 658 | 'pro--gram files' |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 659 | >>> re.sub(r'\sAND\s', ' & ', 'Baked Beans And Spam', flags=re.IGNORECASE) |
| 660 | 'Baked Beans & Spam' |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 661 | |
Georg Brandl | 1b5ab45 | 2009-08-13 07:56:35 +0000 | [diff] [blame] | 662 | The pattern may be a string or an RE object. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 663 | |
| 664 | The optional argument *count* is the maximum number of pattern occurrences to be |
| 665 | replaced; *count* must be a non-negative integer. If omitted or zero, all |
| 666 | occurrences will be replaced. Empty matches for the pattern are replaced only |
| 667 | when not adjacent to a previous match, so ``sub('x*', '-', 'abc')`` returns |
| 668 | ``'-a-b-c-'``. |
| 669 | |
| 670 | In addition to character escapes and backreferences as described above, |
| 671 | ``\g<name>`` will use the substring matched by the group named ``name``, as |
| 672 | defined by the ``(?P<name>...)`` syntax. ``\g<number>`` uses the corresponding |
| 673 | group number; ``\g<2>`` is therefore equivalent to ``\2``, but isn't ambiguous |
| 674 | in a replacement such as ``\g<2>0``. ``\20`` would be interpreted as a |
| 675 | reference to group 20, not a reference to group 2 followed by the literal |
| 676 | character ``'0'``. The backreference ``\g<0>`` substitutes in the entire |
| 677 | substring matched by the RE. |
| 678 | |
Jeroen Ruigrok van der Werven | b70ccc3 | 2009-04-27 08:07:12 +0000 | [diff] [blame] | 679 | .. versionchanged:: 3.1 |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 680 | Added the optional flags argument. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 681 | |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 682 | |
Georg Brandl | 1824415 | 2009-09-02 20:34:52 +0000 | [diff] [blame] | 683 | .. function:: subn(pattern, repl, string, count=0, flags=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 684 | |
| 685 | Perform the same operation as :func:`sub`, but return a tuple ``(new_string, |
| 686 | number_of_subs_made)``. |
| 687 | |
Jeroen Ruigrok van der Werven | b70ccc3 | 2009-04-27 08:07:12 +0000 | [diff] [blame] | 688 | .. versionchanged:: 3.1 |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 689 | Added the optional flags argument. |
| 690 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 691 | |
| 692 | .. function:: escape(string) |
| 693 | |
Ezio Melotti | 88fdeb4 | 2011-04-10 12:59:16 +0300 | [diff] [blame] | 694 | Escape all the characters in pattern except ASCII letters, numbers and ``'_'``. |
| 695 | This is useful if you want to match an arbitrary literal string that may |
| 696 | have regular expression metacharacters in it. |
| 697 | |
| 698 | .. versionchanged:: 3.3 |
| 699 | The ``'_'`` character is no longer escaped. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 700 | |
| 701 | |
R. David Murray | 522c32a | 2010-07-10 14:23:36 +0000 | [diff] [blame] | 702 | .. function:: purge() |
| 703 | |
| 704 | Clear the regular expression cache. |
| 705 | |
| 706 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 707 | .. exception:: error |
| 708 | |
| 709 | Exception raised when a string passed to one of the functions here is not a |
| 710 | valid regular expression (for example, it might contain unmatched parentheses) |
| 711 | or when some other error occurs during compilation or matching. It is never an |
| 712 | error if a string contains no match for a pattern. |
| 713 | |
| 714 | |
| 715 | .. _re-objects: |
| 716 | |
| 717 | Regular Expression Objects |
| 718 | -------------------------- |
| 719 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 720 | Compiled regular expression objects support the following methods and |
Raymond Hettinger | 5768e0c | 2011-10-19 14:10:07 -0700 | [diff] [blame] | 721 | attributes: |
Brian Curtin | 027e478 | 2010-03-26 00:39:56 +0000 | [diff] [blame] | 722 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 723 | .. method:: regex.search(string[, pos[, endpos]]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 724 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 725 | Scan through *string* looking for a location where this regular expression |
| 726 | produces a match, and return a corresponding :ref:`match object |
| 727 | <match-objects>`. Return ``None`` if no position in the string matches the |
| 728 | pattern; note that this is different from finding a zero-length match at some |
| 729 | point in the string. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 730 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 731 | The optional second parameter *pos* gives an index in the string where the |
| 732 | search is to start; it defaults to ``0``. This is not completely equivalent to |
| 733 | slicing the string; the ``'^'`` pattern character matches at the real beginning |
| 734 | of the string and at positions just after a newline, but not necessarily at the |
| 735 | index where the search is to start. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 736 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 737 | The optional parameter *endpos* limits how far the string will be searched; it |
| 738 | will be as if the string is *endpos* characters long, so only the characters |
| 739 | from *pos* to ``endpos - 1`` will be searched for a match. If *endpos* is less |
Raymond Hettinger | 5768e0c | 2011-10-19 14:10:07 -0700 | [diff] [blame] | 740 | than *pos*, no match will be found; otherwise, if *rx* is a compiled regular |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 741 | expression object, ``rx.search(string, 0, 50)`` is equivalent to |
| 742 | ``rx.search(string[:50], 0)``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 743 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 744 | >>> pattern = re.compile("d") |
| 745 | >>> pattern.search("dog") # Match at index 0 |
| 746 | <_sre.SRE_Match object at ...> |
| 747 | >>> pattern.search("dog", 1) # No match; search doesn't include the "d" |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 748 | |
| 749 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 750 | .. method:: regex.match(string[, pos[, endpos]]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 751 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 752 | If zero or more characters at the *beginning* of *string* match this regular |
| 753 | expression, return a corresponding :ref:`match object <match-objects>`. |
| 754 | Return ``None`` if the string does not match the pattern; note that this is |
| 755 | different from a zero-length match. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 756 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 757 | The optional *pos* and *endpos* parameters have the same meaning as for the |
| 758 | :meth:`~regex.search` method. |
Benjamin Peterson | d7c3ed5 | 2010-06-27 22:32:30 +0000 | [diff] [blame] | 759 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 760 | >>> pattern = re.compile("o") |
| 761 | >>> pattern.match("dog") # No match as "o" is not at the start of "dog". |
| 762 | >>> pattern.match("dog", 1) # Match as "o" is the 2nd character of "dog". |
| 763 | <_sre.SRE_Match object at ...> |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 764 | |
Ezio Melotti | 443f000 | 2012-02-29 13:39:05 +0200 | [diff] [blame] | 765 | If you want to locate a match anywhere in *string*, use |
| 766 | :meth:`~regex.search` instead (see also :ref:`search-vs-match`). |
| 767 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 768 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 769 | .. method:: regex.split(string, maxsplit=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 770 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 771 | Identical to the :func:`split` function, using the compiled pattern. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 772 | |
| 773 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 774 | .. method:: regex.findall(string[, pos[, endpos]]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 775 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 776 | Similar to the :func:`findall` function, using the compiled pattern, but |
| 777 | also accepts optional *pos* and *endpos* parameters that limit the search |
| 778 | region like for :meth:`match`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 779 | |
| 780 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 781 | .. method:: regex.finditer(string[, pos[, endpos]]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 782 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 783 | Similar to the :func:`finditer` function, using the compiled pattern, but |
| 784 | also accepts optional *pos* and *endpos* parameters that limit the search |
| 785 | region like for :meth:`match`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 786 | |
| 787 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 788 | .. method:: regex.sub(repl, string, count=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 789 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 790 | Identical to the :func:`sub` function, using the compiled pattern. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 791 | |
| 792 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 793 | .. method:: regex.subn(repl, string, count=0) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 794 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 795 | Identical to the :func:`subn` function, using the compiled pattern. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 796 | |
| 797 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 798 | .. attribute:: regex.flags |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 799 | |
Georg Brandl | 3a19e54 | 2012-03-17 17:29:27 +0100 | [diff] [blame] | 800 | The regex matching flags. This is a combination of the flags given to |
| 801 | :func:`.compile`, any ``(?...)`` inline flags in the pattern, and implicit |
| 802 | flags such as :data:`UNICODE` if the pattern is a Unicode string. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 803 | |
| 804 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 805 | .. attribute:: regex.groups |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 806 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 807 | The number of capturing groups in the pattern. |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 808 | |
| 809 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 810 | .. attribute:: regex.groupindex |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 811 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 812 | A dictionary mapping any symbolic group names defined by ``(?P<id>)`` to group |
| 813 | numbers. The dictionary is empty if no symbolic groups were used in the |
| 814 | pattern. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 815 | |
| 816 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 817 | .. attribute:: regex.pattern |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 818 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 819 | The pattern string from which the RE object was compiled. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 820 | |
| 821 | |
| 822 | .. _match-objects: |
| 823 | |
| 824 | Match Objects |
| 825 | ------------- |
| 826 | |
Ezio Melotti | b87f82f | 2012-11-04 06:59:22 +0200 | [diff] [blame] | 827 | Match objects always have a boolean value of ``True``. |
| 828 | Since :meth:`~regex.match` and :meth:`~regex.search` return ``None`` |
| 829 | when there is no match, you can test whether there was a match with a simple |
| 830 | ``if`` statement:: |
| 831 | |
| 832 | match = re.search(pattern, string) |
| 833 | if match: |
| 834 | process(match) |
| 835 | |
| 836 | Match objects support the following methods and attributes: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 837 | |
| 838 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 839 | .. method:: match.expand(template) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 840 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 841 | Return the string obtained by doing backslash substitution on the template |
| 842 | string *template*, as done by the :meth:`~regex.sub` method. |
| 843 | Escapes such as ``\n`` are converted to the appropriate characters, |
| 844 | and numeric backreferences (``\1``, ``\2``) and named backreferences |
| 845 | (``\g<1>``, ``\g<name>``) are replaced by the contents of the |
| 846 | corresponding group. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 847 | |
| 848 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 849 | .. method:: match.group([group1, ...]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 850 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 851 | Returns one or more subgroups of the match. If there is a single argument, the |
| 852 | result is a single string; if there are multiple arguments, the result is a |
| 853 | tuple with one item per argument. Without arguments, *group1* defaults to zero |
| 854 | (the whole match is returned). If a *groupN* argument is zero, the corresponding |
| 855 | return value is the entire matching string; if it is in the inclusive range |
| 856 | [1..99], it is the string matching the corresponding parenthesized group. If a |
| 857 | group number is negative or larger than the number of groups defined in the |
| 858 | pattern, an :exc:`IndexError` exception is raised. If a group is contained in a |
| 859 | part of the pattern that did not match, the corresponding result is ``None``. |
| 860 | If a group is contained in a part of the pattern that matched multiple times, |
| 861 | the last match is returned. |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 862 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 863 | >>> m = re.match(r"(\w+) (\w+)", "Isaac Newton, physicist") |
| 864 | >>> m.group(0) # The entire match |
| 865 | 'Isaac Newton' |
| 866 | >>> m.group(1) # The first parenthesized subgroup. |
| 867 | 'Isaac' |
| 868 | >>> m.group(2) # The second parenthesized subgroup. |
| 869 | 'Newton' |
| 870 | >>> m.group(1, 2) # Multiple arguments give us a tuple. |
| 871 | ('Isaac', 'Newton') |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 872 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 873 | If the regular expression uses the ``(?P<name>...)`` syntax, the *groupN* |
| 874 | arguments may also be strings identifying groups by their group name. If a |
| 875 | string argument is not used as a group name in the pattern, an :exc:`IndexError` |
| 876 | exception is raised. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 877 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 878 | A moderately complicated example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 879 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 880 | >>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcolm Reynolds") |
| 881 | >>> m.group('first_name') |
| 882 | 'Malcolm' |
| 883 | >>> m.group('last_name') |
| 884 | 'Reynolds' |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 885 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 886 | Named groups can also be referred to by their index: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 887 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 888 | >>> m.group(1) |
| 889 | 'Malcolm' |
| 890 | >>> m.group(2) |
| 891 | 'Reynolds' |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 892 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 893 | If a group matches multiple times, only the last match is accessible: |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 894 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 895 | >>> m = re.match(r"(..)+", "a1b2c3") # Matches 3 times. |
| 896 | >>> m.group(1) # Returns only the last match. |
| 897 | 'c3' |
Brian Curtin | 027e478 | 2010-03-26 00:39:56 +0000 | [diff] [blame] | 898 | |
Brian Curtin | 48f16f9 | 2010-04-08 13:55:29 +0000 | [diff] [blame] | 899 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 900 | .. method:: match.groups(default=None) |
Brian Curtin | 48f16f9 | 2010-04-08 13:55:29 +0000 | [diff] [blame] | 901 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 902 | Return a tuple containing all the subgroups of the match, from 1 up to however |
| 903 | many groups are in the pattern. The *default* argument is used for groups that |
| 904 | did not participate in the match; it defaults to ``None``. |
Brian Curtin | 027e478 | 2010-03-26 00:39:56 +0000 | [diff] [blame] | 905 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 906 | For example: |
Brian Curtin | 027e478 | 2010-03-26 00:39:56 +0000 | [diff] [blame] | 907 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 908 | >>> m = re.match(r"(\d+)\.(\d+)", "24.1632") |
| 909 | >>> m.groups() |
| 910 | ('24', '1632') |
Brian Curtin | 027e478 | 2010-03-26 00:39:56 +0000 | [diff] [blame] | 911 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 912 | If we make the decimal place and everything after it optional, not all groups |
| 913 | might participate in the match. These groups will default to ``None`` unless |
| 914 | the *default* argument is given: |
Brian Curtin | 027e478 | 2010-03-26 00:39:56 +0000 | [diff] [blame] | 915 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 916 | >>> m = re.match(r"(\d+)\.?(\d+)?", "24") |
| 917 | >>> m.groups() # Second group defaults to None. |
| 918 | ('24', None) |
| 919 | >>> m.groups('0') # Now, the second group defaults to '0'. |
| 920 | ('24', '0') |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 921 | |
| 922 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 923 | .. method:: match.groupdict(default=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 924 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 925 | Return a dictionary containing all the *named* subgroups of the match, keyed by |
| 926 | the subgroup name. The *default* argument is used for groups that did not |
| 927 | participate in the match; it defaults to ``None``. For example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 928 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 929 | >>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcolm Reynolds") |
| 930 | >>> m.groupdict() |
| 931 | {'first_name': 'Malcolm', 'last_name': 'Reynolds'} |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 932 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 933 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 934 | .. method:: match.start([group]) |
| 935 | match.end([group]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 936 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 937 | Return the indices of the start and end of the substring matched by *group*; |
| 938 | *group* defaults to zero (meaning the whole matched substring). Return ``-1`` if |
| 939 | *group* exists but did not contribute to the match. For a match object *m*, and |
| 940 | a group *g* that did contribute to the match, the substring matched by group *g* |
| 941 | (equivalent to ``m.group(g)``) is :: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 942 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 943 | m.string[m.start(g):m.end(g)] |
Brian Curtin | 027e478 | 2010-03-26 00:39:56 +0000 | [diff] [blame] | 944 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 945 | Note that ``m.start(group)`` will equal ``m.end(group)`` if *group* matched a |
| 946 | null string. For example, after ``m = re.search('b(c?)', 'cba')``, |
| 947 | ``m.start(0)`` is 1, ``m.end(0)`` is 2, ``m.start(1)`` and ``m.end(1)`` are both |
| 948 | 2, and ``m.start(2)`` raises an :exc:`IndexError` exception. |
Brian Curtin | 027e478 | 2010-03-26 00:39:56 +0000 | [diff] [blame] | 949 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 950 | An example that will remove *remove_this* from email addresses: |
Brian Curtin | 027e478 | 2010-03-26 00:39:56 +0000 | [diff] [blame] | 951 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 952 | >>> email = "tony@tiremove_thisger.net" |
| 953 | >>> m = re.search("remove_this", email) |
| 954 | >>> email[:m.start()] + email[m.end():] |
| 955 | 'tony@tiger.net' |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 956 | |
| 957 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 958 | .. method:: match.span([group]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 959 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 960 | For a match *m*, return the 2-tuple ``(m.start(group), m.end(group))``. Note |
| 961 | that if *group* did not contribute to the match, this is ``(-1, -1)``. |
| 962 | *group* defaults to zero, the entire match. |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 963 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 964 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 965 | .. attribute:: match.pos |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 966 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 967 | The value of *pos* which was passed to the :meth:`~regex.search` or |
Georg Brandl | 69c7a69 | 2012-03-14 08:02:43 +0100 | [diff] [blame] | 968 | :meth:`~regex.match` method of a :ref:`regex object <re-objects>`. This is |
| 969 | the index into the string at which the RE engine started looking for a match. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 970 | |
| 971 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 972 | .. attribute:: match.endpos |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 973 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 974 | The value of *endpos* which was passed to the :meth:`~regex.search` or |
Georg Brandl | 69c7a69 | 2012-03-14 08:02:43 +0100 | [diff] [blame] | 975 | :meth:`~regex.match` method of a :ref:`regex object <re-objects>`. This is |
| 976 | the index into the string beyond which the RE engine will not go. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 977 | |
| 978 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 979 | .. attribute:: match.lastindex |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 980 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 981 | The integer index of the last matched capturing group, or ``None`` if no group |
| 982 | was matched at all. For example, the expressions ``(a)b``, ``((a)(b))``, and |
| 983 | ``((ab))`` will have ``lastindex == 1`` if applied to the string ``'ab'``, while |
| 984 | the expression ``(a)(b)`` will have ``lastindex == 2``, if applied to the same |
| 985 | string. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 986 | |
| 987 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 988 | .. attribute:: match.lastgroup |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 989 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 990 | The name of the last matched capturing group, or ``None`` if the group didn't |
| 991 | have a name, or if no group was matched at all. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 992 | |
| 993 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 994 | .. attribute:: match.re |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 995 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 996 | The regular expression object whose :meth:`~regex.match` or |
| 997 | :meth:`~regex.search` method produced this match instance. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 998 | |
| 999 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 1000 | .. attribute:: match.string |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1001 | |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 1002 | The string passed to :meth:`~regex.match` or :meth:`~regex.search`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1003 | |
| 1004 | |
Raymond Hettinger | 1fa7682 | 2010-12-06 23:31:36 +0000 | [diff] [blame] | 1005 | .. _re-examples: |
| 1006 | |
| 1007 | Regular Expression Examples |
| 1008 | --------------------------- |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1009 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1010 | |
Raymond Hettinger | 5768e0c | 2011-10-19 14:10:07 -0700 | [diff] [blame] | 1011 | Checking for a Pair |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1012 | ^^^^^^^^^^^^^^^^^^^ |
| 1013 | |
| 1014 | In this example, we'll use the following helper function to display match |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1015 | objects a little more gracefully: |
| 1016 | |
| 1017 | .. testcode:: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1018 | |
| 1019 | def displaymatch(match): |
| 1020 | if match is None: |
| 1021 | return None |
| 1022 | return '<Match: %r, groups=%r>' % (match.group(), match.groups()) |
| 1023 | |
| 1024 | Suppose you are writing a poker program where a player's hand is represented as |
| 1025 | a 5-character string with each character representing a card, "a" for ace, "k" |
Ezio Melotti | e5b2ac8 | 2011-12-17 01:17:17 +0200 | [diff] [blame] | 1026 | for king, "q" for queen, "j" for jack, "t" for 10, and "2" through "9" |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1027 | representing the card with that value. |
| 1028 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1029 | To see if a given string is a valid hand, one could do the following: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1030 | |
Ezio Melotti | e5b2ac8 | 2011-12-17 01:17:17 +0200 | [diff] [blame] | 1031 | >>> valid = re.compile(r"^[a2-9tjqk]{5}$") |
| 1032 | >>> displaymatch(valid.match("akt5q")) # Valid. |
| 1033 | "<Match: 'akt5q', groups=()>" |
| 1034 | >>> displaymatch(valid.match("akt5e")) # Invalid. |
| 1035 | >>> displaymatch(valid.match("akt")) # Invalid. |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1036 | >>> displaymatch(valid.match("727ak")) # Valid. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1037 | "<Match: '727ak', groups=()>" |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1038 | |
| 1039 | That last hand, ``"727ak"``, contained a pair, or two of the same valued cards. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1040 | To match this with a regular expression, one could use backreferences as such: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1041 | |
| 1042 | >>> pair = re.compile(r".*(.).*\1") |
| 1043 | >>> displaymatch(pair.match("717ak")) # Pair of 7s. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1044 | "<Match: '717', groups=('7',)>" |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1045 | >>> displaymatch(pair.match("718ak")) # No pairs. |
| 1046 | >>> displaymatch(pair.match("354aa")) # Pair of aces. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1047 | "<Match: '354aa', groups=('a',)>" |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1048 | |
Georg Brandl | f346ac0 | 2009-07-26 15:03:49 +0000 | [diff] [blame] | 1049 | To find out what card the pair consists of, one could use the |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 1050 | :meth:`~match.group` method of the match object in the following manner: |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1051 | |
| 1052 | .. doctest:: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1053 | |
| 1054 | >>> pair.match("717ak").group(1) |
| 1055 | '7' |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1056 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1057 | # Error because re.match() returns None, which doesn't have a group() method: |
| 1058 | >>> pair.match("718ak").group(1) |
| 1059 | Traceback (most recent call last): |
| 1060 | File "<pyshell#23>", line 1, in <module> |
| 1061 | re.match(r".*(.).*\1", "718ak").group(1) |
| 1062 | AttributeError: 'NoneType' object has no attribute 'group' |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1063 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1064 | >>> pair.match("354aa").group(1) |
| 1065 | 'a' |
| 1066 | |
| 1067 | |
| 1068 | Simulating scanf() |
| 1069 | ^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1070 | |
| 1071 | .. index:: single: scanf() |
| 1072 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 1073 | Python does not currently have an equivalent to :c:func:`scanf`. Regular |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1074 | expressions are generally more powerful, though also more verbose, than |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 1075 | :c:func:`scanf` format strings. The table below offers some more-or-less |
| 1076 | equivalent mappings between :c:func:`scanf` format tokens and regular |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1077 | expressions. |
| 1078 | |
| 1079 | +--------------------------------+---------------------------------------------+ |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 1080 | | :c:func:`scanf` Token | Regular Expression | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1081 | +================================+=============================================+ |
| 1082 | | ``%c`` | ``.`` | |
| 1083 | +--------------------------------+---------------------------------------------+ |
| 1084 | | ``%5c`` | ``.{5}`` | |
| 1085 | +--------------------------------+---------------------------------------------+ |
| 1086 | | ``%d`` | ``[-+]?\d+`` | |
| 1087 | +--------------------------------+---------------------------------------------+ |
| 1088 | | ``%e``, ``%E``, ``%f``, ``%g`` | ``[-+]?(\d+(\.\d*)?|\.\d+)([eE][-+]?\d+)?`` | |
| 1089 | +--------------------------------+---------------------------------------------+ |
| 1090 | | ``%i`` | ``[-+]?(0[xX][\dA-Fa-f]+|0[0-7]*|\d+)`` | |
| 1091 | +--------------------------------+---------------------------------------------+ |
Ezio Melotti | a0b1d1e | 2012-04-29 11:47:28 +0300 | [diff] [blame] | 1092 | | ``%o`` | ``[-+]?[0-7]+`` | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1093 | +--------------------------------+---------------------------------------------+ |
| 1094 | | ``%s`` | ``\S+`` | |
| 1095 | +--------------------------------+---------------------------------------------+ |
| 1096 | | ``%u`` | ``\d+`` | |
| 1097 | +--------------------------------+---------------------------------------------+ |
Ezio Melotti | a0b1d1e | 2012-04-29 11:47:28 +0300 | [diff] [blame] | 1098 | | ``%x``, ``%X`` | ``[-+]?(0[xX])?[\dA-Fa-f]+`` | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1099 | +--------------------------------+---------------------------------------------+ |
| 1100 | |
| 1101 | To extract the filename and numbers from a string like :: |
| 1102 | |
| 1103 | /usr/sbin/sendmail - 0 errors, 4 warnings |
| 1104 | |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 1105 | you would use a :c:func:`scanf` format like :: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1106 | |
| 1107 | %s - %d errors, %d warnings |
| 1108 | |
| 1109 | The equivalent regular expression would be :: |
| 1110 | |
| 1111 | (\S+) - (\d+) errors, (\d+) warnings |
| 1112 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1113 | |
Ezio Melotti | 443f000 | 2012-02-29 13:39:05 +0200 | [diff] [blame] | 1114 | .. _search-vs-match: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1115 | |
| 1116 | search() vs. match() |
| 1117 | ^^^^^^^^^^^^^^^^^^^^ |
| 1118 | |
Ezio Melotti | 443f000 | 2012-02-29 13:39:05 +0200 | [diff] [blame] | 1119 | .. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1120 | |
Ezio Melotti | 443f000 | 2012-02-29 13:39:05 +0200 | [diff] [blame] | 1121 | Python offers two different primitive operations based on regular expressions: |
| 1122 | :func:`re.match` checks for a match only at the beginning of the string, while |
| 1123 | :func:`re.search` checks for a match anywhere in the string (this is what Perl |
| 1124 | does by default). |
| 1125 | |
| 1126 | For example:: |
| 1127 | |
| 1128 | >>> re.match("c", "abcdef") # No match |
| 1129 | >>> re.search("c", "abcdef") # Match |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1130 | <_sre.SRE_Match object at ...> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1131 | |
Ezio Melotti | 443f000 | 2012-02-29 13:39:05 +0200 | [diff] [blame] | 1132 | Regular expressions beginning with ``'^'`` can be used with :func:`search` to |
| 1133 | restrict the match at the beginning of the string:: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1134 | |
Ezio Melotti | 443f000 | 2012-02-29 13:39:05 +0200 | [diff] [blame] | 1135 | >>> re.match("c", "abcdef") # No match |
| 1136 | >>> re.search("^c", "abcdef") # No match |
| 1137 | >>> re.search("^a", "abcdef") # Match |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1138 | <_sre.SRE_Match object at ...> |
Ezio Melotti | 443f000 | 2012-02-29 13:39:05 +0200 | [diff] [blame] | 1139 | |
| 1140 | Note however that in :const:`MULTILINE` mode :func:`match` only matches at the |
| 1141 | beginning of the string, whereas using :func:`search` with a regular expression |
| 1142 | beginning with ``'^'`` will match at the beginning of each line. |
| 1143 | |
| 1144 | >>> re.match('X', 'A\nB\nX', re.MULTILINE) # No match |
| 1145 | >>> re.search('^X', 'A\nB\nX', re.MULTILINE) # Match |
| 1146 | <_sre.SRE_Match object at ...> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1147 | |
| 1148 | |
| 1149 | Making a Phonebook |
| 1150 | ^^^^^^^^^^^^^^^^^^ |
| 1151 | |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1152 | :func:`split` splits a string into a list delimited by the passed pattern. The |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1153 | method is invaluable for converting textual data into data structures that can be |
| 1154 | easily read and modified by Python as demonstrated in the following example that |
| 1155 | creates a phonebook. |
| 1156 | |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1157 | First, here is the input. Normally it may come from a file, here we are using |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1158 | triple-quoted string syntax: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1159 | |
Georg Brandl | 557a3ec | 2012-03-17 17:26:27 +0100 | [diff] [blame] | 1160 | >>> text = """Ross McFluff: 834.345.1254 155 Elm Street |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1161 | ... |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1162 | ... Ronald Heathmore: 892.345.3428 436 Finley Avenue |
| 1163 | ... Frank Burger: 925.541.7625 662 South Dogwood Way |
| 1164 | ... |
| 1165 | ... |
| 1166 | ... Heather Albrecht: 548.326.4584 919 Park Place""" |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1167 | |
| 1168 | The entries are separated by one or more newlines. Now we convert the string |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1169 | into a list with each nonempty line having its own entry: |
| 1170 | |
| 1171 | .. doctest:: |
| 1172 | :options: +NORMALIZE_WHITESPACE |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1173 | |
Georg Brandl | 557a3ec | 2012-03-17 17:26:27 +0100 | [diff] [blame] | 1174 | >>> entries = re.split("\n+", text) |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1175 | >>> entries |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1176 | ['Ross McFluff: 834.345.1254 155 Elm Street', |
| 1177 | 'Ronald Heathmore: 892.345.3428 436 Finley Avenue', |
| 1178 | 'Frank Burger: 925.541.7625 662 South Dogwood Way', |
| 1179 | 'Heather Albrecht: 548.326.4584 919 Park Place'] |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1180 | |
| 1181 | Finally, split each entry into a list with first name, last name, telephone |
Christian Heimes | c3f30c4 | 2008-02-22 16:37:40 +0000 | [diff] [blame] | 1182 | number, and address. We use the ``maxsplit`` parameter of :func:`split` |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1183 | because the address has spaces, our splitting pattern, in it: |
| 1184 | |
| 1185 | .. doctest:: |
| 1186 | :options: +NORMALIZE_WHITESPACE |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1187 | |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1188 | >>> [re.split(":? ", entry, 3) for entry in entries] |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1189 | [['Ross', 'McFluff', '834.345.1254', '155 Elm Street'], |
| 1190 | ['Ronald', 'Heathmore', '892.345.3428', '436 Finley Avenue'], |
| 1191 | ['Frank', 'Burger', '925.541.7625', '662 South Dogwood Way'], |
| 1192 | ['Heather', 'Albrecht', '548.326.4584', '919 Park Place']] |
| 1193 | |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1194 | The ``:?`` pattern matches the colon after the last name, so that it does not |
Christian Heimes | c3f30c4 | 2008-02-22 16:37:40 +0000 | [diff] [blame] | 1195 | occur in the result list. With a ``maxsplit`` of ``4``, we could separate the |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1196 | house number from the street name: |
| 1197 | |
| 1198 | .. doctest:: |
| 1199 | :options: +NORMALIZE_WHITESPACE |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1200 | |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1201 | >>> [re.split(":? ", entry, 4) for entry in entries] |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1202 | [['Ross', 'McFluff', '834.345.1254', '155', 'Elm Street'], |
| 1203 | ['Ronald', 'Heathmore', '892.345.3428', '436', 'Finley Avenue'], |
| 1204 | ['Frank', 'Burger', '925.541.7625', '662', 'South Dogwood Way'], |
| 1205 | ['Heather', 'Albrecht', '548.326.4584', '919', 'Park Place']] |
| 1206 | |
| 1207 | |
| 1208 | Text Munging |
| 1209 | ^^^^^^^^^^^^ |
| 1210 | |
| 1211 | :func:`sub` replaces every occurrence of a pattern with a string or the |
| 1212 | result of a function. This example demonstrates using :func:`sub` with |
| 1213 | a function to "munge" text, or randomize the order of all the characters |
| 1214 | in each word of a sentence except for the first and last characters:: |
| 1215 | |
| 1216 | >>> def repl(m): |
| 1217 | ... inner_word = list(m.group(2)) |
| 1218 | ... random.shuffle(inner_word) |
| 1219 | ... return m.group(1) + "".join(inner_word) + m.group(3) |
| 1220 | >>> text = "Professor Abdolmalek, please report your absences promptly." |
Georg Brandl | db4e939 | 2010-07-12 09:06:13 +0000 | [diff] [blame] | 1221 | >>> re.sub(r"(\w)(\w+)(\w)", repl, text) |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1222 | 'Poefsrosr Aealmlobdk, pslaee reorpt your abnseces plmrptoy.' |
Georg Brandl | db4e939 | 2010-07-12 09:06:13 +0000 | [diff] [blame] | 1223 | >>> re.sub(r"(\w)(\w+)(\w)", repl, text) |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1224 | 'Pofsroser Aodlambelk, plasee reoprt yuor asnebces potlmrpy.' |
| 1225 | |
| 1226 | |
| 1227 | Finding all Adverbs |
| 1228 | ^^^^^^^^^^^^^^^^^^^ |
| 1229 | |
Christian Heimes | c3f30c4 | 2008-02-22 16:37:40 +0000 | [diff] [blame] | 1230 | :func:`findall` matches *all* occurrences of a pattern, not just the first |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1231 | one as :func:`search` does. For example, if one was a writer and wanted to |
| 1232 | find all of the adverbs in some text, he or she might use :func:`findall` in |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1233 | the following manner: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1234 | |
| 1235 | >>> text = "He was carefully disguised but captured quickly by police." |
| 1236 | >>> re.findall(r"\w+ly", text) |
| 1237 | ['carefully', 'quickly'] |
| 1238 | |
| 1239 | |
| 1240 | Finding all Adverbs and their Positions |
| 1241 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 1242 | |
| 1243 | If one wants more information about all matches of a pattern than the matched |
Georg Brandl | c62a704 | 2010-07-29 11:49:05 +0000 | [diff] [blame] | 1244 | text, :func:`finditer` is useful as it provides :ref:`match objects |
| 1245 | <match-objects>` instead of strings. Continuing with the previous example, if |
| 1246 | one was a writer who wanted to find all of the adverbs *and their positions* in |
| 1247 | some text, he or she would use :func:`finditer` in the following manner: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1248 | |
| 1249 | >>> text = "He was carefully disguised but captured quickly by police." |
| 1250 | >>> for m in re.finditer(r"\w+ly", text): |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1251 | ... print('%02d-%02d: %s' % (m.start(), m.end(), m.group(0))) |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1252 | 07-16: carefully |
| 1253 | 40-47: quickly |
| 1254 | |
| 1255 | |
| 1256 | Raw String Notation |
| 1257 | ^^^^^^^^^^^^^^^^^^^ |
| 1258 | |
| 1259 | Raw string notation (``r"text"``) keeps regular expressions sane. Without it, |
| 1260 | every backslash (``'\'``) in a regular expression would have to be prefixed with |
| 1261 | another one to escape it. For example, the two following lines of code are |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1262 | functionally identical: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1263 | |
| 1264 | >>> re.match(r"\W(.)\1\W", " ff ") |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1265 | <_sre.SRE_Match object at ...> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1266 | >>> re.match("\\W(.)\\1\\W", " ff ") |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1267 | <_sre.SRE_Match object at ...> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1268 | |
| 1269 | When one wants to match a literal backslash, it must be escaped in the regular |
| 1270 | expression. With raw string notation, this means ``r"\\"``. Without raw string |
| 1271 | notation, one must use ``"\\\\"``, making the following lines of code |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1272 | functionally identical: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1273 | |
| 1274 | >>> re.match(r"\\", r"\\") |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1275 | <_sre.SRE_Match object at ...> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1276 | >>> re.match("\\\\", r"\\") |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1277 | <_sre.SRE_Match object at ...> |
Raymond Hettinger | 37ade9c | 2010-09-16 12:02:17 +0000 | [diff] [blame] | 1278 | |
| 1279 | |
| 1280 | Writing a Tokenizer |
| 1281 | ^^^^^^^^^^^^^^^^^^^ |
| 1282 | |
| 1283 | A `tokenizer or scanner <http://en.wikipedia.org/wiki/Lexical_analysis>`_ |
| 1284 | analyzes a string to categorize groups of characters. This is a useful first |
| 1285 | step in writing a compiler or interpreter. |
| 1286 | |
| 1287 | The text categories are specified with regular expressions. The technique is |
| 1288 | to combine those into a single master regular expression and to loop over |
| 1289 | successive matches:: |
| 1290 | |
Raymond Hettinger | 4b244ef | 2011-05-23 12:45:34 -0700 | [diff] [blame] | 1291 | import collections |
| 1292 | import re |
| 1293 | |
| 1294 | Token = collections.namedtuple('Token', ['typ', 'value', 'line', 'column']) |
Raymond Hettinger | 37ade9c | 2010-09-16 12:02:17 +0000 | [diff] [blame] | 1295 | |
| 1296 | def tokenize(s): |
Raymond Hettinger | 4b244ef | 2011-05-23 12:45:34 -0700 | [diff] [blame] | 1297 | keywords = {'IF', 'THEN', 'ENDIF', 'FOR', 'NEXT', 'GOSUB', 'RETURN'} |
| 1298 | token_specification = [ |
| 1299 | ('NUMBER', r'\d+(\.\d*)?'), # Integer or decimal number |
| 1300 | ('ASSIGN', r':='), # Assignment operator |
| 1301 | ('END', r';'), # Statement terminator |
| 1302 | ('ID', r'[A-Za-z]+'), # Identifiers |
| 1303 | ('OP', r'[+*\/\-]'), # Arithmetic operators |
| 1304 | ('NEWLINE', r'\n'), # Line endings |
| 1305 | ('SKIP', r'[ \t]'), # Skip over spaces and tabs |
Raymond Hettinger | 37ade9c | 2010-09-16 12:02:17 +0000 | [diff] [blame] | 1306 | ] |
Raymond Hettinger | 4b244ef | 2011-05-23 12:45:34 -0700 | [diff] [blame] | 1307 | tok_regex = '|'.join('(?P<%s>%s)' % pair for pair in token_specification) |
| 1308 | get_token = re.compile(tok_regex).match |
Raymond Hettinger | 37ade9c | 2010-09-16 12:02:17 +0000 | [diff] [blame] | 1309 | line = 1 |
| 1310 | pos = line_start = 0 |
Raymond Hettinger | 4b244ef | 2011-05-23 12:45:34 -0700 | [diff] [blame] | 1311 | mo = get_token(s) |
Raymond Hettinger | 37ade9c | 2010-09-16 12:02:17 +0000 | [diff] [blame] | 1312 | while mo is not None: |
| 1313 | typ = mo.lastgroup |
| 1314 | if typ == 'NEWLINE': |
| 1315 | line_start = pos |
| 1316 | line += 1 |
| 1317 | elif typ != 'SKIP': |
Georg Brandl | 325477e | 2011-05-13 06:54:23 +0200 | [diff] [blame] | 1318 | val = mo.group(typ) |
Raymond Hettinger | c2c7c37 | 2010-12-07 09:44:21 +0000 | [diff] [blame] | 1319 | if typ == 'ID' and val in keywords: |
| 1320 | typ = val |
Georg Brandl | 325477e | 2011-05-13 06:54:23 +0200 | [diff] [blame] | 1321 | yield Token(typ, val, line, mo.start()-line_start) |
Raymond Hettinger | 37ade9c | 2010-09-16 12:02:17 +0000 | [diff] [blame] | 1322 | pos = mo.end() |
Raymond Hettinger | 4b244ef | 2011-05-23 12:45:34 -0700 | [diff] [blame] | 1323 | mo = get_token(s, pos) |
Raymond Hettinger | 37ade9c | 2010-09-16 12:02:17 +0000 | [diff] [blame] | 1324 | if pos != len(s): |
| 1325 | raise RuntimeError('Unexpected character %r on line %d' %(s[pos], line)) |
| 1326 | |
Raymond Hettinger | 4b244ef | 2011-05-23 12:45:34 -0700 | [diff] [blame] | 1327 | statements = ''' |
| 1328 | IF quantity THEN |
| 1329 | total := total + price * quantity; |
| 1330 | tax := price * 0.05; |
| 1331 | ENDIF; |
Raymond Hettinger | 37ade9c | 2010-09-16 12:02:17 +0000 | [diff] [blame] | 1332 | ''' |
Raymond Hettinger | 23157e5 | 2011-05-13 01:38:31 -0700 | [diff] [blame] | 1333 | |
| 1334 | for token in tokenize(statements): |
| 1335 | print(token) |
| 1336 | |
| 1337 | The tokenizer produces the following output:: |
Raymond Hettinger | 9c47d77 | 2011-05-13 01:03:50 -0700 | [diff] [blame] | 1338 | |
Raymond Hettinger | 4b244ef | 2011-05-23 12:45:34 -0700 | [diff] [blame] | 1339 | Token(typ='IF', value='IF', line=2, column=5) |
| 1340 | Token(typ='ID', value='quantity', line=2, column=8) |
| 1341 | Token(typ='THEN', value='THEN', line=2, column=17) |
| 1342 | Token(typ='ID', value='total', line=3, column=9) |
| 1343 | Token(typ='ASSIGN', value=':=', line=3, column=15) |
| 1344 | Token(typ='ID', value='total', line=3, column=18) |
| 1345 | Token(typ='OP', value='+', line=3, column=24) |
| 1346 | Token(typ='ID', value='price', line=3, column=26) |
| 1347 | Token(typ='OP', value='*', line=3, column=32) |
| 1348 | Token(typ='ID', value='quantity', line=3, column=34) |
| 1349 | Token(typ='END', value=';', line=3, column=42) |
| 1350 | Token(typ='ID', value='tax', line=4, column=9) |
| 1351 | Token(typ='ASSIGN', value=':=', line=4, column=13) |
| 1352 | Token(typ='ID', value='price', line=4, column=16) |
| 1353 | Token(typ='OP', value='*', line=4, column=22) |
| 1354 | Token(typ='NUMBER', value='0.05', line=4, column=24) |
| 1355 | Token(typ='END', value=';', line=4, column=28) |
| 1356 | Token(typ='ENDIF', value='ENDIF', line=5, column=5) |
| 1357 | Token(typ='END', value=';', line=5, column=10) |