Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1 | |
| 2 | :mod:`re` --- Regular expression operations |
| 3 | =========================================== |
| 4 | |
| 5 | .. module:: re |
| 6 | :synopsis: Regular expression operations. |
| 7 | .. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com> |
| 8 | .. sectionauthor:: Andrew M. Kuchling <amk@amk.ca> |
| 9 | |
| 10 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 11 | This module provides regular expression matching operations similar to |
Georg Brandl | ed2a1db | 2009-06-08 07:48:27 +0000 | [diff] [blame] | 12 | those found in Perl. |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 13 | |
| 14 | Both patterns and strings to be searched can be Unicode strings as well as |
| 15 | 8-bit strings. However, Unicode strings and 8-bit strings cannot be mixed: |
| 16 | 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] | 17 | vice-versa; similarly, when asking for a substitution, the replacement |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 18 | 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] | 19 | |
| 20 | Regular expressions use the backslash character (``'\'``) to indicate |
| 21 | special forms or to allow special characters to be used without invoking |
| 22 | their special meaning. This collides with Python's usage of the same |
| 23 | character for the same purpose in string literals; for example, to match |
| 24 | a literal backslash, one might have to write ``'\\\\'`` as the pattern |
| 25 | string, because the regular expression must be ``\\``, and each |
| 26 | backslash must be expressed as ``\\`` inside a regular Python string |
| 27 | literal. |
| 28 | |
| 29 | The solution is to use Python's raw string notation for regular expression |
| 30 | patterns; backslashes are not handled in any special way in a string literal |
| 31 | prefixed with ``'r'``. So ``r"\n"`` is a two-character string containing |
| 32 | ``'\'`` and ``'n'``, while ``"\n"`` is a one-character string containing a |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 33 | newline. Usually patterns will be expressed in Python code using this raw |
| 34 | string notation. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 35 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 36 | It is important to note that most regular expression operations are available as |
| 37 | module-level functions and :class:`RegexObject` methods. The functions are |
| 38 | shortcuts that don't require you to compile a regex object first, but miss some |
| 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 |
| 83 | the null byte using the ``\number`` notation, e.g., ``'\x00'``. |
| 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 | ``[]`` |
| 164 | Used to indicate a set of characters. Characters can be listed individually, or |
| 165 | a range of characters can be indicated by giving two characters and separating |
| 166 | them by a ``'-'``. Special characters are not active inside sets. For example, |
| 167 | ``[akm$]`` will match any of the characters ``'a'``, ``'k'``, |
| 168 | ``'m'``, or ``'$'``; ``[a-z]`` will match any lowercase letter, and |
| 169 | ``[a-zA-Z0-9]`` matches any letter or digit. Character classes such |
| 170 | as ``\w`` or ``\S`` (defined below) are also acceptable inside a |
Mark Summerfield | 8676534 | 2008-08-20 07:40:18 +0000 | [diff] [blame] | 171 | range, although the characters they match depends on whether |
| 172 | :const:`ASCII` or :const:`LOCALE` mode is in force. If you want to |
| 173 | include a ``']'`` or a ``'-'`` inside a set, precede it with a |
| 174 | backslash, or place it as the first character. The pattern ``[]]`` |
| 175 | will match ``']'``, for example. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 176 | |
| 177 | You can match the characters not within a range by :dfn:`complementing` the set. |
| 178 | This is indicated by including a ``'^'`` as the first character of the set; |
| 179 | ``'^'`` elsewhere will simply match the ``'^'`` character. For example, |
| 180 | ``[^5]`` will match any character except ``'5'``, and ``[^^]`` will match any |
| 181 | character except ``'^'``. |
| 182 | |
Mark Summerfield | 9e670c2 | 2008-05-31 13:05:34 +0000 | [diff] [blame] | 183 | Note that inside ``[]`` the special forms and special characters lose |
| 184 | their meanings and only the syntaxes described here are valid. For |
| 185 | example, ``+``, ``*``, ``(``, ``)``, and so on are treated as |
| 186 | literals inside ``[]``, and backreferences cannot be used inside |
| 187 | ``[]``. |
| 188 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 189 | ``'|'`` |
| 190 | ``A|B``, where A and B can be arbitrary REs, creates a regular expression that |
| 191 | will match either A or B. An arbitrary number of REs can be separated by the |
| 192 | ``'|'`` in this way. This can be used inside groups (see below) as well. As |
| 193 | the target string is scanned, REs separated by ``'|'`` are tried from left to |
| 194 | right. When one pattern completely matches, that branch is accepted. This means |
| 195 | that once ``A`` matches, ``B`` will not be tested further, even if it would |
| 196 | produce a longer overall match. In other words, the ``'|'`` operator is never |
| 197 | greedy. To match a literal ``'|'``, use ``\|``, or enclose it inside a |
| 198 | character class, as in ``[|]``. |
| 199 | |
| 200 | ``(...)`` |
| 201 | Matches whatever regular expression is inside the parentheses, and indicates the |
| 202 | start and end of a group; the contents of a group can be retrieved after a match |
| 203 | has been performed, and can be matched later in the string with the ``\number`` |
| 204 | special sequence, described below. To match the literals ``'('`` or ``')'``, |
| 205 | use ``\(`` or ``\)``, or enclose them inside a character class: ``[(] [)]``. |
| 206 | |
| 207 | ``(?...)`` |
| 208 | This is an extension notation (a ``'?'`` following a ``'('`` is not meaningful |
| 209 | otherwise). The first character after the ``'?'`` determines what the meaning |
| 210 | and further syntax of the construct is. Extensions usually do not create a new |
| 211 | group; ``(?P<name>...)`` is the only exception to this rule. Following are the |
| 212 | currently supported extensions. |
| 213 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 214 | ``(?aiLmsux)`` |
| 215 | (One or more letters from the set ``'a'``, ``'i'``, ``'L'``, ``'m'``, |
| 216 | ``'s'``, ``'u'``, ``'x'``.) The group matches the empty string; the |
Andrew M. Kuchling | 1c50e86 | 2009-06-01 00:11:36 +0000 | [diff] [blame] | 217 | letters set the corresponding flags: :const:`re.A` (ASCII-only matching), |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 218 | :const:`re.I` (ignore case), :const:`re.L` (locale dependent), |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 219 | :const:`re.M` (multi-line), :const:`re.S` (dot matches all), |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 220 | and :const:`re.X` (verbose), for the entire regular expression. (The |
| 221 | flags are described in :ref:`contents-of-module-re`.) This |
| 222 | is useful if you wish to include the flags as part of the regular |
| 223 | expression, instead of passing a *flag* argument to the |
| 224 | :func:`compile` function. |
| 225 | |
| 226 | Note that the ``(?x)`` flag changes how the expression is parsed. It should be |
| 227 | used first in the expression string, or after one or more whitespace characters. |
| 228 | If there are non-whitespace characters before the flag, the results are |
| 229 | undefined. |
| 230 | |
| 231 | ``(?:...)`` |
| 232 | A non-grouping version of regular parentheses. Matches whatever regular |
| 233 | expression is inside the parentheses, but the substring matched by the group |
| 234 | *cannot* be retrieved after performing a match or referenced later in the |
| 235 | pattern. |
| 236 | |
| 237 | ``(?P<name>...)`` |
| 238 | Similar to regular parentheses, but the substring matched by the group is |
Benjamin Peterson | d23f822 | 2009-04-05 19:13:16 +0000 | [diff] [blame] | 239 | accessible within the rest of the regular expression via the symbolic group |
| 240 | name *name*. Group names must be valid Python identifiers, and each group |
| 241 | name must be defined only once within a regular expression. A symbolic group |
| 242 | is also a numbered group, just as if the group were not named. So the group |
| 243 | named ``id`` in the example below can also be referenced as the numbered group |
| 244 | ``1``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 245 | |
| 246 | For example, if the pattern is ``(?P<id>[a-zA-Z_]\w*)``, the group can be |
| 247 | 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] | 248 | ``m.group('id')`` or ``m.end('id')``, and also by name in the regular |
| 249 | expression itself (using ``(?P=id)``) and replacement text given to |
| 250 | ``.sub()`` (using ``\g<id>``). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 251 | |
| 252 | ``(?P=name)`` |
| 253 | Matches whatever text was matched by the earlier group named *name*. |
| 254 | |
| 255 | ``(?#...)`` |
| 256 | A comment; the contents of the parentheses are simply ignored. |
| 257 | |
| 258 | ``(?=...)`` |
| 259 | Matches if ``...`` matches next, but doesn't consume any of the string. This is |
| 260 | called a lookahead assertion. For example, ``Isaac (?=Asimov)`` will match |
| 261 | ``'Isaac '`` only if it's followed by ``'Asimov'``. |
| 262 | |
| 263 | ``(?!...)`` |
| 264 | Matches if ``...`` doesn't match next. This is a negative lookahead assertion. |
| 265 | For example, ``Isaac (?!Asimov)`` will match ``'Isaac '`` only if it's *not* |
| 266 | followed by ``'Asimov'``. |
| 267 | |
| 268 | ``(?<=...)`` |
| 269 | Matches if the current position in the string is preceded by a match for ``...`` |
| 270 | that ends at the current position. This is called a :dfn:`positive lookbehind |
| 271 | assertion`. ``(?<=abc)def`` will find a match in ``abcdef``, since the |
| 272 | lookbehind will back up 3 characters and check if the contained pattern matches. |
| 273 | The contained pattern must only match strings of some fixed length, meaning that |
| 274 | ``abc`` or ``a|b`` are allowed, but ``a*`` and ``a{3,4}`` are not. Note that |
| 275 | patterns which start with positive lookbehind assertions will never match at the |
| 276 | 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] | 277 | :func:`search` function rather than the :func:`match` function: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 278 | |
| 279 | >>> import re |
| 280 | >>> m = re.search('(?<=abc)def', 'abcdef') |
| 281 | >>> m.group(0) |
| 282 | 'def' |
| 283 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 284 | This example looks for a word following a hyphen: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 285 | |
| 286 | >>> m = re.search('(?<=-)\w+', 'spam-egg') |
| 287 | >>> m.group(0) |
| 288 | 'egg' |
| 289 | |
| 290 | ``(?<!...)`` |
| 291 | Matches if the current position in the string is not preceded by a match for |
| 292 | ``...``. This is called a :dfn:`negative lookbehind assertion`. Similar to |
| 293 | positive lookbehind assertions, the contained pattern must only match strings of |
| 294 | some fixed length. Patterns which start with negative lookbehind assertions may |
| 295 | match at the beginning of the string being searched. |
| 296 | |
| 297 | ``(?(id/name)yes-pattern|no-pattern)`` |
| 298 | Will try to match with ``yes-pattern`` if the group with given *id* or *name* |
| 299 | exists, and with ``no-pattern`` if it doesn't. ``no-pattern`` is optional and |
| 300 | can be omitted. For example, ``(<)?(\w+@\w+(?:\.\w+)+)(?(1)>)`` is a poor email |
| 301 | matching pattern, which will match with ``'<user@host.com>'`` as well as |
| 302 | ``'user@host.com'``, but not with ``'<user@host.com'``. |
| 303 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 304 | |
| 305 | The special sequences consist of ``'\'`` and a character from the list below. |
| 306 | If the ordinary character is not on the list, then the resulting RE will match |
| 307 | the second character. For example, ``\$`` matches the character ``'$'``. |
| 308 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 309 | ``\number`` |
| 310 | Matches the contents of the group of the same number. Groups are numbered |
| 311 | starting from 1. For example, ``(.+) \1`` matches ``'the the'`` or ``'55 55'``, |
| 312 | but not ``'the end'`` (note the space after the group). This special sequence |
| 313 | can only be used to match one of the first 99 groups. If the first digit of |
| 314 | *number* is 0, or *number* is 3 octal digits long, it will not be interpreted as |
| 315 | a group match, but as the character with octal value *number*. Inside the |
| 316 | ``'['`` and ``']'`` of a character class, all numeric escapes are treated as |
| 317 | characters. |
| 318 | |
| 319 | ``\A`` |
| 320 | Matches only at the start of the string. |
| 321 | |
| 322 | ``\b`` |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 323 | Matches the empty string, but only at the beginning or end of a word. |
| 324 | A word is defined as a sequence of Unicode alphanumeric or underscore |
| 325 | characters, so the end of a word is indicated by whitespace or a |
| 326 | non-alphanumeric, non-underscore Unicode character. Note that |
| 327 | formally, ``\b`` is defined as the boundary between a ``\w`` and a |
| 328 | ``\W`` character (or vice versa). By default Unicode alphanumerics |
| 329 | are the ones used, but this can be changed by using the :const:`ASCII` |
| 330 | flag. Inside a character range, ``\b`` represents the backspace |
| 331 | character, for compatibility with Python's string literals. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 332 | |
| 333 | ``\B`` |
| 334 | Matches the empty string, but only when it is *not* at the beginning or end of a |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 335 | word. This is just the opposite of ``\b``, so word characters are |
| 336 | Unicode alphanumerics or the underscore, although this can be changed |
| 337 | by using the :const:`ASCII` flag. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 338 | |
| 339 | ``\d`` |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 340 | For Unicode (str) patterns: |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 341 | Matches any Unicode digit (which includes ``[0-9]``, and also many |
| 342 | other digit characters). If the :const:`ASCII` flag is used only |
| 343 | ``[0-9]`` is matched (but the flag affects the entire regular |
| 344 | expression, so in such cases using an explicit ``[0-9]`` may be a |
| 345 | better choice). |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 346 | For 8-bit (bytes) patterns: |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 347 | Matches any decimal digit; this is equivalent to ``[0-9]``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 348 | |
| 349 | ``\D`` |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 350 | Matches any character which is not a Unicode decimal digit. This is |
| 351 | the opposite of ``\d``. If the :const:`ASCII` flag is used this |
| 352 | becomes the equivalent of ``[^0-9]`` (but the flag affects the entire |
| 353 | regular expression, so in such cases using an explicit ``[^0-9]`` may |
| 354 | be a better choice). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 355 | |
| 356 | ``\s`` |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 357 | For Unicode (str) patterns: |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 358 | Matches Unicode whitespace characters (which includes |
| 359 | ``[ \t\n\r\f\v]``, and also many other characters, for example the |
| 360 | non-breaking spaces mandated by typography rules in many |
| 361 | languages). If the :const:`ASCII` flag is used, only |
| 362 | ``[ \t\n\r\f\v]`` is matched (but the flag affects the entire |
| 363 | regular expression, so in such cases using an explicit |
| 364 | ``[ \t\n\r\f\v]`` may be a better choice). |
| 365 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 366 | For 8-bit (bytes) patterns: |
| 367 | Matches characters considered whitespace in the ASCII character set; |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 368 | this is equivalent to ``[ \t\n\r\f\v]``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 369 | |
| 370 | ``\S`` |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 371 | Matches any character which is not a Unicode whitespace character. This is |
| 372 | the opposite of ``\s``. If the :const:`ASCII` flag is used this |
| 373 | becomes the equivalent of ``[^ \t\n\r\f\v]`` (but the flag affects the entire |
| 374 | regular expression, so in such cases using an explicit ``[^ \t\n\r\f\v]`` may |
| 375 | be a better choice). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 376 | |
| 377 | ``\w`` |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 378 | For Unicode (str) patterns: |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 379 | Matches Unicode word characters; this includes most characters |
| 380 | that can be part of a word in any language, as well as numbers and |
| 381 | the underscore. If the :const:`ASCII` flag is used, only |
| 382 | ``[a-zA-Z0-9_]`` is matched (but the flag affects the entire |
| 383 | regular expression, so in such cases using an explicit |
| 384 | ``[a-zA-Z0-9_]`` may be a better choice). |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 385 | For 8-bit (bytes) patterns: |
| 386 | Matches characters considered alphanumeric in the ASCII character set; |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 387 | this is equivalent to ``[a-zA-Z0-9_]``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 388 | |
| 389 | ``\W`` |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 390 | Matches any character which is not a Unicode word character. This is |
| 391 | the opposite of ``\w``. If the :const:`ASCII` flag is used this |
| 392 | becomes the equivalent of ``[^a-zA-Z0-9_]`` (but the flag affects the |
| 393 | entire regular expression, so in such cases using an explicit |
| 394 | ``[^a-zA-Z0-9_]`` may be a better choice). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 395 | |
| 396 | ``\Z`` |
| 397 | Matches only at the end of the string. |
| 398 | |
| 399 | Most of the standard escapes supported by Python string literals are also |
| 400 | accepted by the regular expression parser:: |
| 401 | |
| 402 | \a \b \f \n |
| 403 | \r \t \v \x |
| 404 | \\ |
| 405 | |
| 406 | Octal escapes are included in a limited form: If the first digit is a 0, or if |
| 407 | there are three octal digits, it is considered an octal escape. Otherwise, it is |
| 408 | a group reference. As for string literals, octal escapes are always at most |
| 409 | three digits in length. |
| 410 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 411 | |
| 412 | .. _matching-searching: |
| 413 | |
| 414 | Matching vs Searching |
| 415 | --------------------- |
| 416 | |
| 417 | .. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org> |
| 418 | |
| 419 | |
| 420 | Python offers two different primitive operations based on regular expressions: |
Guido van Rossum | 04110fb | 2007-08-24 16:32:05 +0000 | [diff] [blame] | 421 | **match** checks for a match only at the beginning of the string, while |
| 422 | **search** checks for a match anywhere in the string (this is what Perl does |
| 423 | by default). |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 424 | |
Guido van Rossum | 04110fb | 2007-08-24 16:32:05 +0000 | [diff] [blame] | 425 | Note that match may differ from search even when using a regular expression |
| 426 | beginning with ``'^'``: ``'^'`` matches only at the start of the string, or in |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 427 | :const:`MULTILINE` mode also immediately following a newline. The "match" |
| 428 | operation succeeds only if the pattern matches at the start of the string |
| 429 | regardless of mode, or at the starting position given by the optional *pos* |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 430 | argument regardless of whether a newline precedes it. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 431 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 432 | >>> re.match("c", "abcdef") # No match |
| 433 | >>> re.search("c", "abcdef") # Match |
| 434 | <_sre.SRE_Match object at ...> |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 435 | |
| 436 | |
| 437 | .. _contents-of-module-re: |
| 438 | |
| 439 | Module Contents |
| 440 | --------------- |
| 441 | |
| 442 | The module defines several functions, constants, and an exception. Some of the |
| 443 | functions are simplified versions of the full featured methods for compiled |
| 444 | regular expressions. Most non-trivial applications always use the compiled |
| 445 | form. |
| 446 | |
| 447 | |
| 448 | .. function:: compile(pattern[, flags]) |
| 449 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 450 | Compile a regular expression pattern into a regular expression object, which |
| 451 | 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] | 452 | described below. |
| 453 | |
| 454 | The expression's behaviour can be modified by specifying a *flags* value. |
| 455 | Values can be any of the following variables, combined using bitwise OR (the |
| 456 | ``|`` operator). |
| 457 | |
| 458 | The sequence :: |
| 459 | |
Gregory P. Smith | 4221c74 | 2009-03-02 05:04:04 +0000 | [diff] [blame] | 460 | prog = re.compile(pattern) |
| 461 | result = prog.match(string) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 462 | |
| 463 | is equivalent to :: |
| 464 | |
Gregory P. Smith | 4221c74 | 2009-03-02 05:04:04 +0000 | [diff] [blame] | 465 | result = re.match(pattern, string) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 466 | |
Gregory P. Smith | 4221c74 | 2009-03-02 05:04:04 +0000 | [diff] [blame] | 467 | but using :func:`compile` and saving the resulting regular expression object |
| 468 | for reuse is more efficient when the expression will be used several times |
| 469 | in a single program. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 470 | |
Gregory P. Smith | 4221c74 | 2009-03-02 05:04:04 +0000 | [diff] [blame] | 471 | .. note:: |
| 472 | |
| 473 | The compiled versions of the most recent patterns passed to |
| 474 | :func:`re.match`, :func:`re.search` or :func:`re.compile` are cached, so |
| 475 | programs that use only a few regular expressions at a time needn't worry |
| 476 | about compiling regular expressions. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 477 | |
| 478 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 479 | .. data:: A |
| 480 | ASCII |
| 481 | |
Georg Brandl | 4049ce0 | 2009-06-08 07:49:54 +0000 | [diff] [blame] | 482 | Make ``\w``, ``\W``, ``\b``, ``\B``, ``\d``, ``\D``, ``\s`` and ``\S`` |
| 483 | perform ASCII-only matching instead of full Unicode matching. This is only |
| 484 | meaningful for Unicode patterns, and is ignored for byte patterns. |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 485 | |
Mark Summerfield | 6c4f617 | 2008-08-20 07:34:41 +0000 | [diff] [blame] | 486 | Note that for backward compatibility, the :const:`re.U` flag still |
| 487 | exists (as well as its synonym :const:`re.UNICODE` and its embedded |
| 488 | counterpart ``(?u)``), but these are redundant in Python 3.0 since |
| 489 | matches are Unicode by default for strings (and Unicode matching |
| 490 | isn't allowed for bytes). |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 491 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 492 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 493 | .. data:: I |
| 494 | IGNORECASE |
| 495 | |
| 496 | Perform case-insensitive matching; expressions like ``[A-Z]`` will match |
Mark Summerfield | 8676534 | 2008-08-20 07:40:18 +0000 | [diff] [blame] | 497 | lowercase letters, too. This is not affected by the current locale |
| 498 | and works for Unicode characters as expected. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 499 | |
| 500 | |
| 501 | .. data:: L |
| 502 | LOCALE |
| 503 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 504 | Make ``\w``, ``\W``, ``\b``, ``\B``, ``\s`` and ``\S`` dependent on the |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 505 | current locale. The use of this flag is discouraged as the locale mechanism |
| 506 | is very unreliable, and it only handles one "culture" at a time anyway; |
| 507 | you should use Unicode matching instead, which is the default in Python 3.0 |
| 508 | for Unicode (str) patterns. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 509 | |
| 510 | |
| 511 | .. data:: M |
| 512 | MULTILINE |
| 513 | |
| 514 | When specified, the pattern character ``'^'`` matches at the beginning of the |
| 515 | string and at the beginning of each line (immediately following each newline); |
| 516 | and the pattern character ``'$'`` matches at the end of the string and at the |
| 517 | end of each line (immediately preceding each newline). By default, ``'^'`` |
| 518 | matches only at the beginning of the string, and ``'$'`` only at the end of the |
| 519 | string and immediately before the newline (if any) at the end of the string. |
| 520 | |
| 521 | |
| 522 | .. data:: S |
| 523 | DOTALL |
| 524 | |
| 525 | Make the ``'.'`` special character match any character at all, including a |
| 526 | newline; without this flag, ``'.'`` will match anything *except* a newline. |
| 527 | |
| 528 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 529 | .. data:: X |
| 530 | VERBOSE |
| 531 | |
| 532 | This flag allows you to write regular expressions that look nicer. Whitespace |
| 533 | within the pattern is ignored, except when in a character class or preceded by |
| 534 | an unescaped backslash, and, when a line contains a ``'#'`` neither in a |
| 535 | character class or preceded by an unescaped backslash, all characters from the |
| 536 | leftmost such ``'#'`` through the end of the line are ignored. |
| 537 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 538 | That means that the two following regular expression objects that match a |
| 539 | decimal number are functionally equal:: |
Georg Brandl | 81ac1ce | 2007-08-31 17:17:17 +0000 | [diff] [blame] | 540 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 541 | a = re.compile(r"""\d + # the integral part |
| 542 | \. # the decimal point |
| 543 | \d * # some fractional digits""", re.X) |
| 544 | b = re.compile(r"\d+\.\d*") |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 545 | |
| 546 | |
Antoine Pitrou | fd03645 | 2008-08-19 17:56:33 +0000 | [diff] [blame] | 547 | |
| 548 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 549 | .. function:: search(pattern, string[, flags]) |
| 550 | |
| 551 | Scan through *string* looking for a location where the regular expression |
| 552 | *pattern* produces a match, and return a corresponding :class:`MatchObject` |
| 553 | instance. Return ``None`` if no position in the string matches the pattern; note |
| 554 | that this is different from finding a zero-length match at some point in the |
| 555 | string. |
| 556 | |
| 557 | |
| 558 | .. function:: match(pattern, string[, flags]) |
| 559 | |
| 560 | If zero or more characters at the beginning of *string* match the regular |
| 561 | expression *pattern*, return a corresponding :class:`MatchObject` instance. |
| 562 | Return ``None`` if the string does not match the pattern; note that this is |
| 563 | different from a zero-length match. |
| 564 | |
| 565 | .. note:: |
| 566 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 567 | If you want to locate a match anywhere in *string*, use :meth:`search` |
| 568 | instead. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 569 | |
| 570 | |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 571 | .. function:: split(pattern, string[, maxsplit=0, flags=0]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 572 | |
| 573 | Split *string* by the occurrences of *pattern*. If capturing parentheses are |
| 574 | used in *pattern*, then the text of all groups in the pattern are also returned |
| 575 | as part of the resulting list. If *maxsplit* is nonzero, at most *maxsplit* |
| 576 | 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] | 577 | of the list. :: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 578 | |
| 579 | >>> re.split('\W+', 'Words, words, words.') |
| 580 | ['Words', 'words', 'words', ''] |
| 581 | >>> re.split('(\W+)', 'Words, words, words.') |
| 582 | ['Words', ', ', 'words', ', ', 'words', '.', ''] |
| 583 | >>> re.split('\W+', 'Words, words, words.', 1) |
| 584 | ['Words', 'words, words.'] |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 585 | >>> re.split('[a-f]+', '0a3B9', flags=re.IGNORECASE) |
| 586 | ['0', '3', '9'] |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 587 | |
Christian Heimes | dd15f6c | 2008-03-16 00:07:10 +0000 | [diff] [blame] | 588 | If there are capturing groups in the separator and it matches at the start of |
| 589 | 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] | 590 | the end of the string: |
Christian Heimes | dd15f6c | 2008-03-16 00:07:10 +0000 | [diff] [blame] | 591 | |
| 592 | >>> re.split('(\W+)', '...words, words...') |
| 593 | ['', '...', 'words', ', ', 'words', '...', ''] |
| 594 | |
| 595 | That way, separator components are always found at the same relative |
| 596 | indices within the result list (e.g., if there's one capturing group |
| 597 | in the separator, the 0th, the 2nd and so forth). |
| 598 | |
Thomas Wouters | 89d996e | 2007-09-08 17:39:28 +0000 | [diff] [blame] | 599 | 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] | 600 | For example: |
Thomas Wouters | 89d996e | 2007-09-08 17:39:28 +0000 | [diff] [blame] | 601 | |
| 602 | >>> re.split('x*', 'foo') |
| 603 | ['foo'] |
| 604 | >>> re.split("(?m)^$", "foo\n\nbar\n") |
| 605 | ['foo\n\nbar\n'] |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 606 | |
Jeroen Ruigrok van der Werven | b70ccc3 | 2009-04-27 08:07:12 +0000 | [diff] [blame] | 607 | .. versionchanged:: 3.1 |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 608 | Added the optional flags argument. |
| 609 | |
Christian Heimes | dd15f6c | 2008-03-16 00:07:10 +0000 | [diff] [blame] | 610 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 611 | .. function:: findall(pattern, string[, flags]) |
| 612 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 613 | 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] | 614 | strings. The *string* is scanned left-to-right, and matches are returned in |
| 615 | the order found. If one or more groups are present in the pattern, return a |
| 616 | list of groups; this will be a list of tuples if the pattern has more than |
| 617 | one group. Empty matches are included in the result unless they touch the |
| 618 | beginning of another match. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 619 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 620 | |
| 621 | .. function:: finditer(pattern, string[, flags]) |
| 622 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 623 | Return an :term:`iterator` yielding :class:`MatchObject` instances over all |
Georg Brandl | 3dbca81 | 2008-07-23 16:10:53 +0000 | [diff] [blame] | 624 | non-overlapping matches for the RE *pattern* in *string*. The *string* is |
| 625 | scanned left-to-right, and matches are returned in the order found. Empty |
| 626 | matches are included in the result unless they touch the beginning of another |
| 627 | match. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 628 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 629 | |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 630 | .. function:: sub(pattern, repl, string[, count, flags]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 631 | |
| 632 | Return the string obtained by replacing the leftmost non-overlapping occurrences |
| 633 | of *pattern* in *string* by the replacement *repl*. If the pattern isn't found, |
| 634 | *string* is returned unchanged. *repl* can be a string or a function; if it is |
| 635 | a string, any backslash escapes in it are processed. That is, ``\n`` is |
| 636 | converted to a single newline character, ``\r`` is converted to a linefeed, and |
| 637 | so forth. Unknown escapes such as ``\j`` are left alone. Backreferences, such |
| 638 | 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] | 639 | For example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 640 | |
| 641 | >>> re.sub(r'def\s+([a-zA-Z_][a-zA-Z_0-9]*)\s*\(\s*\):', |
| 642 | ... r'static PyObject*\npy_\1(void)\n{', |
| 643 | ... 'def myfunc():') |
| 644 | 'static PyObject*\npy_myfunc(void)\n{' |
| 645 | |
| 646 | If *repl* is a function, it is called for every non-overlapping occurrence of |
| 647 | *pattern*. The function takes a single match object argument, and returns the |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 648 | replacement string. For example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 649 | |
| 650 | >>> def dashrepl(matchobj): |
| 651 | ... if matchobj.group(0) == '-': return ' ' |
| 652 | ... else: return '-' |
| 653 | >>> re.sub('-{1,2}', dashrepl, 'pro----gram-files') |
| 654 | 'pro--gram files' |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 655 | >>> re.sub(r'\sAND\s', ' & ', 'Baked Beans And Spam', flags=re.IGNORECASE) |
| 656 | 'Baked Beans & Spam' |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 657 | |
| 658 | The pattern may be a string or an RE object; if you need to specify regular |
| 659 | expression flags, you must use a RE object, or use embedded modifiers in a |
| 660 | pattern; for example, ``sub("(?i)b+", "x", "bbbb BBBB")`` returns ``'x x'``. |
| 661 | |
| 662 | The optional argument *count* is the maximum number of pattern occurrences to be |
| 663 | replaced; *count* must be a non-negative integer. If omitted or zero, all |
| 664 | occurrences will be replaced. Empty matches for the pattern are replaced only |
| 665 | when not adjacent to a previous match, so ``sub('x*', '-', 'abc')`` returns |
| 666 | ``'-a-b-c-'``. |
| 667 | |
| 668 | In addition to character escapes and backreferences as described above, |
| 669 | ``\g<name>`` will use the substring matched by the group named ``name``, as |
| 670 | defined by the ``(?P<name>...)`` syntax. ``\g<number>`` uses the corresponding |
| 671 | group number; ``\g<2>`` is therefore equivalent to ``\2``, but isn't ambiguous |
| 672 | in a replacement such as ``\g<2>0``. ``\20`` would be interpreted as a |
| 673 | reference to group 20, not a reference to group 2 followed by the literal |
| 674 | character ``'0'``. The backreference ``\g<0>`` substitutes in the entire |
| 675 | substring matched by the RE. |
| 676 | |
Jeroen Ruigrok van der Werven | b70ccc3 | 2009-04-27 08:07:12 +0000 | [diff] [blame] | 677 | .. versionchanged:: 3.1 |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 678 | Added the optional flags argument. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 679 | |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 680 | |
| 681 | .. function:: subn(pattern, repl, string[, count, flags]) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 682 | |
| 683 | Perform the same operation as :func:`sub`, but return a tuple ``(new_string, |
| 684 | number_of_subs_made)``. |
| 685 | |
Jeroen Ruigrok van der Werven | b70ccc3 | 2009-04-27 08:07:12 +0000 | [diff] [blame] | 686 | .. versionchanged:: 3.1 |
Gregory P. Smith | ccc5ae7 | 2009-03-02 05:21:55 +0000 | [diff] [blame] | 687 | Added the optional flags argument. |
| 688 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 689 | |
| 690 | .. function:: escape(string) |
| 691 | |
| 692 | Return *string* with all non-alphanumerics backslashed; this is useful if you |
| 693 | want to match an arbitrary literal string that may have regular expression |
| 694 | metacharacters in it. |
| 695 | |
| 696 | |
| 697 | .. exception:: error |
| 698 | |
| 699 | Exception raised when a string passed to one of the functions here is not a |
| 700 | valid regular expression (for example, it might contain unmatched parentheses) |
| 701 | or when some other error occurs during compilation or matching. It is never an |
| 702 | error if a string contains no match for a pattern. |
| 703 | |
| 704 | |
| 705 | .. _re-objects: |
| 706 | |
| 707 | Regular Expression Objects |
| 708 | -------------------------- |
| 709 | |
| 710 | Compiled regular expression objects support the following methods and |
| 711 | attributes: |
| 712 | |
| 713 | |
| 714 | .. method:: RegexObject.match(string[, pos[, endpos]]) |
| 715 | |
| 716 | If zero or more characters at the beginning of *string* match this regular |
| 717 | expression, return a corresponding :class:`MatchObject` instance. Return |
| 718 | ``None`` if the string does not match the pattern; note that this is different |
| 719 | from a zero-length match. |
| 720 | |
| 721 | .. note:: |
| 722 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 723 | If you want to locate a match anywhere in *string*, use :meth:`search` |
| 724 | instead. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 725 | |
| 726 | The optional second parameter *pos* gives an index in the string where the |
| 727 | search is to start; it defaults to ``0``. This is not completely equivalent to |
| 728 | slicing the string; the ``'^'`` pattern character matches at the real beginning |
| 729 | of the string and at positions just after a newline, but not necessarily at the |
| 730 | index where the search is to start. |
| 731 | |
| 732 | The optional parameter *endpos* limits how far the string will be searched; it |
| 733 | will be as if the string is *endpos* characters long, so only the characters |
| 734 | from *pos* to ``endpos - 1`` will be searched for a match. If *endpos* is less |
| 735 | than *pos*, no match will be found, otherwise, if *rx* is a compiled regular |
| 736 | expression object, ``rx.match(string, 0, 50)`` is equivalent to |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 737 | ``rx.match(string[:50], 0)``. |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 738 | |
| 739 | >>> pattern = re.compile("o") |
| 740 | >>> pattern.match("dog") # No match as "o" is not at the start of "dog." |
| 741 | >>> pattern.match("dog", 1) # Match as "o" is the 2nd character of "dog". |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 742 | <_sre.SRE_Match object at ...> |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 743 | |
| 744 | |
| 745 | .. method:: RegexObject.search(string[, pos[, endpos]]) |
| 746 | |
| 747 | Scan through *string* looking for a location where this regular expression |
| 748 | produces a match, and return a corresponding :class:`MatchObject` instance. |
| 749 | Return ``None`` if no position in the string matches the pattern; note that this |
| 750 | is different from finding a zero-length match at some point in the string. |
| 751 | |
| 752 | The optional *pos* and *endpos* parameters have the same meaning as for the |
| 753 | :meth:`match` method. |
| 754 | |
| 755 | |
| 756 | .. method:: RegexObject.split(string[, maxsplit=0]) |
| 757 | |
| 758 | Identical to the :func:`split` function, using the compiled pattern. |
| 759 | |
| 760 | |
| 761 | .. method:: RegexObject.findall(string[, pos[, endpos]]) |
| 762 | |
| 763 | Identical to the :func:`findall` function, using the compiled pattern. |
| 764 | |
| 765 | |
| 766 | .. method:: RegexObject.finditer(string[, pos[, endpos]]) |
| 767 | |
| 768 | Identical to the :func:`finditer` function, using the compiled pattern. |
| 769 | |
| 770 | |
| 771 | .. method:: RegexObject.sub(repl, string[, count=0]) |
| 772 | |
| 773 | Identical to the :func:`sub` function, using the compiled pattern. |
| 774 | |
| 775 | |
| 776 | .. method:: RegexObject.subn(repl, string[, count=0]) |
| 777 | |
| 778 | Identical to the :func:`subn` function, using the compiled pattern. |
| 779 | |
| 780 | |
| 781 | .. attribute:: RegexObject.flags |
| 782 | |
| 783 | The flags argument used when the RE object was compiled, or ``0`` if no flags |
| 784 | were provided. |
| 785 | |
| 786 | |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 787 | .. attribute:: RegexObject.groups |
| 788 | |
| 789 | The number of capturing groups in the pattern. |
| 790 | |
| 791 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 792 | .. attribute:: RegexObject.groupindex |
| 793 | |
| 794 | A dictionary mapping any symbolic group names defined by ``(?P<id>)`` to group |
| 795 | numbers. The dictionary is empty if no symbolic groups were used in the |
| 796 | pattern. |
| 797 | |
| 798 | |
| 799 | .. attribute:: RegexObject.pattern |
| 800 | |
| 801 | The pattern string from which the RE object was compiled. |
| 802 | |
| 803 | |
| 804 | .. _match-objects: |
| 805 | |
| 806 | Match Objects |
| 807 | ------------- |
| 808 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 809 | Match objects always have a boolean value of :const:`True`, so that you can test |
| 810 | whether e.g. :func:`match` resulted in a match with a simple if statement. They |
| 811 | support the following methods and attributes: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 812 | |
| 813 | |
| 814 | .. method:: MatchObject.expand(template) |
| 815 | |
| 816 | Return the string obtained by doing backslash substitution on the template |
| 817 | string *template*, as done by the :meth:`sub` method. Escapes such as ``\n`` are |
| 818 | converted to the appropriate characters, and numeric backreferences (``\1``, |
| 819 | ``\2``) and named backreferences (``\g<1>``, ``\g<name>``) are replaced by the |
| 820 | contents of the corresponding group. |
| 821 | |
| 822 | |
| 823 | .. method:: MatchObject.group([group1, ...]) |
| 824 | |
| 825 | Returns one or more subgroups of the match. If there is a single argument, the |
| 826 | result is a single string; if there are multiple arguments, the result is a |
| 827 | tuple with one item per argument. Without arguments, *group1* defaults to zero |
| 828 | (the whole match is returned). If a *groupN* argument is zero, the corresponding |
| 829 | return value is the entire matching string; if it is in the inclusive range |
| 830 | [1..99], it is the string matching the corresponding parenthesized group. If a |
| 831 | group number is negative or larger than the number of groups defined in the |
| 832 | pattern, an :exc:`IndexError` exception is raised. If a group is contained in a |
| 833 | part of the pattern that did not match, the corresponding result is ``None``. |
| 834 | If a group is contained in a part of the pattern that matched multiple times, |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 835 | the last match is returned. |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 836 | |
| 837 | >>> m = re.match(r"(\w+) (\w+)", "Isaac Newton, physicist") |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 838 | >>> m.group(0) # The entire match |
| 839 | 'Isaac Newton' |
| 840 | >>> m.group(1) # The first parenthesized subgroup. |
| 841 | 'Isaac' |
| 842 | >>> m.group(2) # The second parenthesized subgroup. |
| 843 | 'Newton' |
| 844 | >>> m.group(1, 2) # Multiple arguments give us a tuple. |
| 845 | ('Isaac', 'Newton') |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 846 | |
| 847 | If the regular expression uses the ``(?P<name>...)`` syntax, the *groupN* |
| 848 | arguments may also be strings identifying groups by their group name. If a |
| 849 | string argument is not used as a group name in the pattern, an :exc:`IndexError` |
| 850 | exception is raised. |
| 851 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 852 | A moderately complicated example: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 853 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 854 | >>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcom Reynolds") |
| 855 | >>> m.group('first_name') |
| 856 | 'Malcom' |
| 857 | >>> m.group('last_name') |
| 858 | 'Reynolds' |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 859 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 860 | Named groups can also be referred to by their index: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 861 | |
| 862 | >>> m.group(1) |
| 863 | 'Malcom' |
| 864 | >>> m.group(2) |
| 865 | 'Reynolds' |
| 866 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 867 | If a group matches multiple times, only the last match is accessible: |
| 868 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 869 | >>> m = re.match(r"(..)+", "a1b2c3") # Matches 3 times. |
| 870 | >>> m.group(1) # Returns only the last match. |
| 871 | 'c3' |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 872 | |
| 873 | |
| 874 | .. method:: MatchObject.groups([default]) |
| 875 | |
| 876 | Return a tuple containing all the subgroups of the match, from 1 up to however |
| 877 | many groups are in the pattern. The *default* argument is used for groups that |
Georg Brandl | 9647389 | 2008-03-06 07:09:43 +0000 | [diff] [blame] | 878 | did not participate in the match; it defaults to ``None``. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 879 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 880 | For example: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 881 | |
| 882 | >>> m = re.match(r"(\d+)\.(\d+)", "24.1632") |
| 883 | >>> m.groups() |
| 884 | ('24', '1632') |
| 885 | |
| 886 | If we make the decimal place and everything after it optional, not all groups |
| 887 | might participate in the match. These groups will default to ``None`` unless |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 888 | the *default* argument is given: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 889 | |
| 890 | >>> m = re.match(r"(\d+)\.?(\d+)?", "24") |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 891 | >>> m.groups() # Second group defaults to None. |
| 892 | ('24', None) |
| 893 | >>> m.groups('0') # Now, the second group defaults to '0'. |
| 894 | ('24', '0') |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 895 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 896 | |
| 897 | .. method:: MatchObject.groupdict([default]) |
| 898 | |
| 899 | Return a dictionary containing all the *named* subgroups of the match, keyed by |
| 900 | the subgroup name. The *default* argument is used for groups that did not |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 901 | participate in the match; it defaults to ``None``. For example: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 902 | |
| 903 | >>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcom Reynolds") |
| 904 | >>> m.groupdict() |
| 905 | {'first_name': 'Malcom', 'last_name': 'Reynolds'} |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 906 | |
| 907 | |
| 908 | .. method:: MatchObject.start([group]) |
| 909 | MatchObject.end([group]) |
| 910 | |
| 911 | Return the indices of the start and end of the substring matched by *group*; |
| 912 | *group* defaults to zero (meaning the whole matched substring). Return ``-1`` if |
| 913 | *group* exists but did not contribute to the match. For a match object *m*, and |
| 914 | a group *g* that did contribute to the match, the substring matched by group *g* |
| 915 | (equivalent to ``m.group(g)``) is :: |
| 916 | |
| 917 | m.string[m.start(g):m.end(g)] |
| 918 | |
| 919 | Note that ``m.start(group)`` will equal ``m.end(group)`` if *group* matched a |
| 920 | null string. For example, after ``m = re.search('b(c?)', 'cba')``, |
| 921 | ``m.start(0)`` is 1, ``m.end(0)`` is 2, ``m.start(1)`` and ``m.end(1)`` are both |
| 922 | 2, and ``m.start(2)`` raises an :exc:`IndexError` exception. |
| 923 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 924 | An example that will remove *remove_this* from email addresses: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 925 | |
| 926 | >>> email = "tony@tiremove_thisger.net" |
| 927 | >>> m = re.search("remove_this", email) |
| 928 | >>> email[:m.start()] + email[m.end():] |
| 929 | 'tony@tiger.net' |
| 930 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 931 | |
| 932 | .. method:: MatchObject.span([group]) |
| 933 | |
| 934 | For :class:`MatchObject` *m*, return the 2-tuple ``(m.start(group), |
| 935 | m.end(group))``. Note that if *group* did not contribute to the match, this is |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 936 | ``(-1, -1)``. *group* defaults to zero, the entire match. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 937 | |
| 938 | |
| 939 | .. attribute:: MatchObject.pos |
| 940 | |
| 941 | The value of *pos* which was passed to the :func:`search` or :func:`match` |
| 942 | method of the :class:`RegexObject`. This is the index into the string at which |
| 943 | the RE engine started looking for a match. |
| 944 | |
| 945 | |
| 946 | .. attribute:: MatchObject.endpos |
| 947 | |
| 948 | The value of *endpos* which was passed to the :func:`search` or :func:`match` |
| 949 | method of the :class:`RegexObject`. This is the index into the string beyond |
| 950 | which the RE engine will not go. |
| 951 | |
| 952 | |
| 953 | .. attribute:: MatchObject.lastindex |
| 954 | |
| 955 | The integer index of the last matched capturing group, or ``None`` if no group |
| 956 | was matched at all. For example, the expressions ``(a)b``, ``((a)(b))``, and |
| 957 | ``((ab))`` will have ``lastindex == 1`` if applied to the string ``'ab'``, while |
| 958 | the expression ``(a)(b)`` will have ``lastindex == 2``, if applied to the same |
| 959 | string. |
| 960 | |
| 961 | |
| 962 | .. attribute:: MatchObject.lastgroup |
| 963 | |
| 964 | The name of the last matched capturing group, or ``None`` if the group didn't |
| 965 | have a name, or if no group was matched at all. |
| 966 | |
| 967 | |
| 968 | .. attribute:: MatchObject.re |
| 969 | |
| 970 | The regular expression object whose :meth:`match` or :meth:`search` method |
| 971 | produced this :class:`MatchObject` instance. |
| 972 | |
| 973 | |
| 974 | .. attribute:: MatchObject.string |
| 975 | |
| 976 | The string passed to :func:`match` or :func:`search`. |
| 977 | |
| 978 | |
| 979 | Examples |
| 980 | -------- |
| 981 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 982 | |
| 983 | Checking For a Pair |
| 984 | ^^^^^^^^^^^^^^^^^^^ |
| 985 | |
| 986 | 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] | 987 | objects a little more gracefully: |
| 988 | |
| 989 | .. testcode:: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 990 | |
| 991 | def displaymatch(match): |
| 992 | if match is None: |
| 993 | return None |
| 994 | return '<Match: %r, groups=%r>' % (match.group(), match.groups()) |
| 995 | |
| 996 | Suppose you are writing a poker program where a player's hand is represented as |
| 997 | a 5-character string with each character representing a card, "a" for ace, "k" |
| 998 | for king, "q" for queen, j for jack, "0" for 10, and "1" through "9" |
| 999 | representing the card with that value. |
| 1000 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1001 | 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] | 1002 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1003 | >>> valid = re.compile(r"[0-9akqj]{5}$") |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1004 | >>> displaymatch(valid.match("ak05q")) # Valid. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1005 | "<Match: 'ak05q', groups=()>" |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1006 | >>> displaymatch(valid.match("ak05e")) # Invalid. |
| 1007 | >>> displaymatch(valid.match("ak0")) # Invalid. |
| 1008 | >>> displaymatch(valid.match("727ak")) # Valid. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1009 | "<Match: '727ak', groups=()>" |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1010 | |
| 1011 | 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] | 1012 | 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] | 1013 | |
| 1014 | >>> pair = re.compile(r".*(.).*\1") |
| 1015 | >>> displaymatch(pair.match("717ak")) # Pair of 7s. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1016 | "<Match: '717', groups=('7',)>" |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1017 | >>> displaymatch(pair.match("718ak")) # No pairs. |
| 1018 | >>> displaymatch(pair.match("354aa")) # Pair of aces. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1019 | "<Match: '354aa', groups=('a',)>" |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1020 | |
| 1021 | To find out what card the pair consists of, one could use the :func:`group` |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1022 | method of :class:`MatchObject` in the following manner: |
| 1023 | |
| 1024 | .. doctest:: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1025 | |
| 1026 | >>> pair.match("717ak").group(1) |
| 1027 | '7' |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1028 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1029 | # Error because re.match() returns None, which doesn't have a group() method: |
| 1030 | >>> pair.match("718ak").group(1) |
| 1031 | Traceback (most recent call last): |
| 1032 | File "<pyshell#23>", line 1, in <module> |
| 1033 | re.match(r".*(.).*\1", "718ak").group(1) |
| 1034 | AttributeError: 'NoneType' object has no attribute 'group' |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1035 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1036 | >>> pair.match("354aa").group(1) |
| 1037 | 'a' |
| 1038 | |
| 1039 | |
| 1040 | Simulating scanf() |
| 1041 | ^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1042 | |
| 1043 | .. index:: single: scanf() |
| 1044 | |
| 1045 | Python does not currently have an equivalent to :cfunc:`scanf`. Regular |
| 1046 | expressions are generally more powerful, though also more verbose, than |
| 1047 | :cfunc:`scanf` format strings. The table below offers some more-or-less |
| 1048 | equivalent mappings between :cfunc:`scanf` format tokens and regular |
| 1049 | expressions. |
| 1050 | |
| 1051 | +--------------------------------+---------------------------------------------+ |
| 1052 | | :cfunc:`scanf` Token | Regular Expression | |
| 1053 | +================================+=============================================+ |
| 1054 | | ``%c`` | ``.`` | |
| 1055 | +--------------------------------+---------------------------------------------+ |
| 1056 | | ``%5c`` | ``.{5}`` | |
| 1057 | +--------------------------------+---------------------------------------------+ |
| 1058 | | ``%d`` | ``[-+]?\d+`` | |
| 1059 | +--------------------------------+---------------------------------------------+ |
| 1060 | | ``%e``, ``%E``, ``%f``, ``%g`` | ``[-+]?(\d+(\.\d*)?|\.\d+)([eE][-+]?\d+)?`` | |
| 1061 | +--------------------------------+---------------------------------------------+ |
| 1062 | | ``%i`` | ``[-+]?(0[xX][\dA-Fa-f]+|0[0-7]*|\d+)`` | |
| 1063 | +--------------------------------+---------------------------------------------+ |
| 1064 | | ``%o`` | ``0[0-7]*`` | |
| 1065 | +--------------------------------+---------------------------------------------+ |
| 1066 | | ``%s`` | ``\S+`` | |
| 1067 | +--------------------------------+---------------------------------------------+ |
| 1068 | | ``%u`` | ``\d+`` | |
| 1069 | +--------------------------------+---------------------------------------------+ |
| 1070 | | ``%x``, ``%X`` | ``0[xX][\dA-Fa-f]+`` | |
| 1071 | +--------------------------------+---------------------------------------------+ |
| 1072 | |
| 1073 | To extract the filename and numbers from a string like :: |
| 1074 | |
| 1075 | /usr/sbin/sendmail - 0 errors, 4 warnings |
| 1076 | |
| 1077 | you would use a :cfunc:`scanf` format like :: |
| 1078 | |
| 1079 | %s - %d errors, %d warnings |
| 1080 | |
| 1081 | The equivalent regular expression would be :: |
| 1082 | |
| 1083 | (\S+) - (\d+) errors, (\d+) warnings |
| 1084 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1085 | |
| 1086 | Avoiding recursion |
| 1087 | ^^^^^^^^^^^^^^^^^^ |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1088 | |
| 1089 | If you create regular expressions that require the engine to perform a lot of |
| 1090 | recursion, you may encounter a :exc:`RuntimeError` exception with the message |
| 1091 | ``maximum recursion limit`` exceeded. For example, :: |
| 1092 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1093 | >>> s = 'Begin ' + 1000*'a very long string ' + 'end' |
| 1094 | >>> re.match('Begin (\w| )*? end', s).end() |
| 1095 | Traceback (most recent call last): |
| 1096 | File "<stdin>", line 1, in ? |
| 1097 | File "/usr/local/lib/python2.5/re.py", line 132, in match |
| 1098 | return _compile(pattern, flags).match(string) |
| 1099 | RuntimeError: maximum recursion limit exceeded |
| 1100 | |
| 1101 | You can often restructure your regular expression to avoid recursion. |
| 1102 | |
Georg Brandl | e6bcc91 | 2008-05-12 18:05:20 +0000 | [diff] [blame] | 1103 | Simple uses of the ``*?`` pattern are special-cased to avoid recursion. Thus, |
| 1104 | the above regular expression can avoid recursion by being recast as ``Begin |
| 1105 | [a-zA-Z0-9_ ]*?end``. As a further benefit, such regular expressions will run |
| 1106 | faster than their recursive equivalents. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1107 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1108 | |
| 1109 | search() vs. match() |
| 1110 | ^^^^^^^^^^^^^^^^^^^^ |
| 1111 | |
| 1112 | In a nutshell, :func:`match` only attempts to match a pattern at the beginning |
| 1113 | of a string where :func:`search` will match a pattern anywhere in a string. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1114 | For example: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1115 | |
| 1116 | >>> re.match("o", "dog") # No match as "o" is not the first letter of "dog". |
| 1117 | >>> re.search("o", "dog") # Match as search() looks everywhere in the string. |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1118 | <_sre.SRE_Match object at ...> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1119 | |
| 1120 | .. note:: |
| 1121 | |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1122 | The following applies only to regular expression objects like those created |
| 1123 | with ``re.compile("pattern")``, not the primitives ``re.match(pattern, |
| 1124 | string)`` or ``re.search(pattern, string)``. |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1125 | |
| 1126 | :func:`match` has an optional second parameter that gives an index in the string |
Benjamin Peterson | f07d002 | 2009-03-21 17:31:58 +0000 | [diff] [blame] | 1127 | where the search is to start:: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1128 | |
| 1129 | >>> pattern = re.compile("o") |
| 1130 | >>> pattern.match("dog") # No match as "o" is not at the start of "dog." |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1131 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1132 | # Equivalent to the above expression as 0 is the default starting index: |
| 1133 | >>> pattern.match("dog", 0) |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1134 | |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1135 | # Match as "o" is the 2nd character of "dog" (index 0 is the first): |
| 1136 | >>> pattern.match("dog", 1) |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1137 | <_sre.SRE_Match object at ...> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1138 | >>> pattern.match("dog", 2) # No match as "o" is not the 3rd character of "dog." |
| 1139 | |
| 1140 | |
| 1141 | Making a Phonebook |
| 1142 | ^^^^^^^^^^^^^^^^^^ |
| 1143 | |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1144 | :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] | 1145 | method is invaluable for converting textual data into data structures that can be |
| 1146 | easily read and modified by Python as demonstrated in the following example that |
| 1147 | creates a phonebook. |
| 1148 | |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1149 | 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] | 1150 | triple-quoted string syntax: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1151 | |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1152 | >>> input = """Ross McFluff: 834.345.1254 155 Elm Street |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 1153 | ... |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1154 | ... Ronald Heathmore: 892.345.3428 436 Finley Avenue |
| 1155 | ... Frank Burger: 925.541.7625 662 South Dogwood Way |
| 1156 | ... |
| 1157 | ... |
| 1158 | ... Heather Albrecht: 548.326.4584 919 Park Place""" |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1159 | |
| 1160 | 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] | 1161 | into a list with each nonempty line having its own entry: |
| 1162 | |
| 1163 | .. doctest:: |
| 1164 | :options: +NORMALIZE_WHITESPACE |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1165 | |
| 1166 | >>> entries = re.split("\n+", input) |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1167 | >>> entries |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1168 | ['Ross McFluff: 834.345.1254 155 Elm Street', |
| 1169 | 'Ronald Heathmore: 892.345.3428 436 Finley Avenue', |
| 1170 | 'Frank Burger: 925.541.7625 662 South Dogwood Way', |
| 1171 | 'Heather Albrecht: 548.326.4584 919 Park Place'] |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1172 | |
| 1173 | 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] | 1174 | number, and address. We use the ``maxsplit`` parameter of :func:`split` |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1175 | because the address has spaces, our splitting pattern, in it: |
| 1176 | |
| 1177 | .. doctest:: |
| 1178 | :options: +NORMALIZE_WHITESPACE |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1179 | |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1180 | >>> [re.split(":? ", entry, 3) for entry in entries] |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1181 | [['Ross', 'McFluff', '834.345.1254', '155 Elm Street'], |
| 1182 | ['Ronald', 'Heathmore', '892.345.3428', '436 Finley Avenue'], |
| 1183 | ['Frank', 'Burger', '925.541.7625', '662 South Dogwood Way'], |
| 1184 | ['Heather', 'Albrecht', '548.326.4584', '919 Park Place']] |
| 1185 | |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1186 | 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] | 1187 | 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] | 1188 | house number from the street name: |
| 1189 | |
| 1190 | .. doctest:: |
| 1191 | :options: +NORMALIZE_WHITESPACE |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1192 | |
Christian Heimes | 255f53b | 2007-12-08 15:33:56 +0000 | [diff] [blame] | 1193 | >>> [re.split(":? ", entry, 4) for entry in entries] |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1194 | [['Ross', 'McFluff', '834.345.1254', '155', 'Elm Street'], |
| 1195 | ['Ronald', 'Heathmore', '892.345.3428', '436', 'Finley Avenue'], |
| 1196 | ['Frank', 'Burger', '925.541.7625', '662', 'South Dogwood Way'], |
| 1197 | ['Heather', 'Albrecht', '548.326.4584', '919', 'Park Place']] |
| 1198 | |
| 1199 | |
| 1200 | Text Munging |
| 1201 | ^^^^^^^^^^^^ |
| 1202 | |
| 1203 | :func:`sub` replaces every occurrence of a pattern with a string or the |
| 1204 | result of a function. This example demonstrates using :func:`sub` with |
| 1205 | a function to "munge" text, or randomize the order of all the characters |
| 1206 | in each word of a sentence except for the first and last characters:: |
| 1207 | |
| 1208 | >>> def repl(m): |
| 1209 | ... inner_word = list(m.group(2)) |
| 1210 | ... random.shuffle(inner_word) |
| 1211 | ... return m.group(1) + "".join(inner_word) + m.group(3) |
| 1212 | >>> text = "Professor Abdolmalek, please report your absences promptly." |
| 1213 | >>> re.sub("(\w)(\w+)(\w)", repl, text) |
| 1214 | 'Poefsrosr Aealmlobdk, pslaee reorpt your abnseces plmrptoy.' |
| 1215 | >>> re.sub("(\w)(\w+)(\w)", repl, text) |
| 1216 | 'Pofsroser Aodlambelk, plasee reoprt yuor asnebces potlmrpy.' |
| 1217 | |
| 1218 | |
| 1219 | Finding all Adverbs |
| 1220 | ^^^^^^^^^^^^^^^^^^^ |
| 1221 | |
Christian Heimes | c3f30c4 | 2008-02-22 16:37:40 +0000 | [diff] [blame] | 1222 | :func:`findall` matches *all* occurrences of a pattern, not just the first |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1223 | one as :func:`search` does. For example, if one was a writer and wanted to |
| 1224 | 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] | 1225 | the following manner: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1226 | |
| 1227 | >>> text = "He was carefully disguised but captured quickly by police." |
| 1228 | >>> re.findall(r"\w+ly", text) |
| 1229 | ['carefully', 'quickly'] |
| 1230 | |
| 1231 | |
| 1232 | Finding all Adverbs and their Positions |
| 1233 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 1234 | |
| 1235 | If one wants more information about all matches of a pattern than the matched |
| 1236 | text, :func:`finditer` is useful as it provides instances of |
| 1237 | :class:`MatchObject` instead of strings. Continuing with the previous example, |
| 1238 | if one was a writer who wanted to find all of the adverbs *and their positions* |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1239 | in 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] | 1240 | |
| 1241 | >>> text = "He was carefully disguised but captured quickly by police." |
| 1242 | >>> for m in re.finditer(r"\w+ly", text): |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1243 | ... print('%02d-%02d: %s' % (m.start(), m.end(), m.group(0))) |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1244 | 07-16: carefully |
| 1245 | 40-47: quickly |
| 1246 | |
| 1247 | |
| 1248 | Raw String Notation |
| 1249 | ^^^^^^^^^^^^^^^^^^^ |
| 1250 | |
| 1251 | Raw string notation (``r"text"``) keeps regular expressions sane. Without it, |
| 1252 | every backslash (``'\'``) in a regular expression would have to be prefixed with |
| 1253 | 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] | 1254 | functionally identical: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1255 | |
| 1256 | >>> re.match(r"\W(.)\1\W", " ff ") |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1257 | <_sre.SRE_Match object at ...> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1258 | >>> re.match("\\W(.)\\1\\W", " ff ") |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1259 | <_sre.SRE_Match object at ...> |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1260 | |
| 1261 | When one wants to match a literal backslash, it must be escaped in the regular |
| 1262 | expression. With raw string notation, this means ``r"\\"``. Without raw string |
| 1263 | notation, one must use ``"\\\\"``, making the following lines of code |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1264 | functionally identical: |
Christian Heimes | b9eccbf | 2007-12-05 20:18:38 +0000 | [diff] [blame] | 1265 | |
| 1266 | >>> re.match(r"\\", r"\\") |
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 | >>> re.match("\\\\", r"\\") |
Christian Heimes | fe337bf | 2008-03-23 21:54:12 +0000 | [diff] [blame] | 1269 | <_sre.SRE_Match object at ...> |