| :mod:`re` --- Regular expression operations |
| =========================================== |
| |
| .. module:: re |
| :synopsis: Regular expression operations. |
| .. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com> |
| .. sectionauthor:: Andrew M. Kuchling <amk@amk.ca> |
| |
| |
| This module provides regular expression matching operations similar to |
| those found in Perl. |
| |
| Both patterns and strings to be searched can be Unicode strings as well as |
| 8-bit strings. However, Unicode strings and 8-bit strings cannot be mixed: |
| that is, you cannot match an Unicode string with a byte pattern or |
| vice-versa; similarly, when asking for a substitution, the replacement |
| string must be of the same type as both the pattern and the search string. |
| |
| Regular expressions use the backslash character (``'\'``) to indicate |
| special forms or to allow special characters to be used without invoking |
| their special meaning. This collides with Python's usage of the same |
| character for the same purpose in string literals; for example, to match |
| a literal backslash, one might have to write ``'\\\\'`` as the pattern |
| string, because the regular expression must be ``\\``, and each |
| backslash must be expressed as ``\\`` inside a regular Python string |
| literal. |
| |
| The solution is to use Python's raw string notation for regular expression |
| patterns; backslashes are not handled in any special way in a string literal |
| prefixed with ``'r'``. So ``r"\n"`` is a two-character string containing |
| ``'\'`` and ``'n'``, while ``"\n"`` is a one-character string containing a |
| newline. Usually patterns will be expressed in Python code using this raw |
| string notation. |
| |
| It is important to note that most regular expression operations are available as |
| module-level functions and methods on |
| :ref:`compiled regular expressions <re-objects>`. The functions are shortcuts |
| that don't require you to compile a regex object first, but miss some |
| fine-tuning parameters. |
| |
| .. seealso:: |
| |
| Mastering Regular Expressions |
| Book on regular expressions by Jeffrey Friedl, published by O'Reilly. The |
| second edition of the book no longer covers Python at all, but the first |
| edition covered writing good regular expression patterns in great detail. |
| |
| |
| .. _re-syntax: |
| |
| Regular Expression Syntax |
| ------------------------- |
| |
| A regular expression (or RE) specifies a set of strings that matches it; the |
| functions in this module let you check if a particular string matches a given |
| regular expression (or if a given regular expression matches a particular |
| string, which comes down to the same thing). |
| |
| Regular expressions can be concatenated to form new regular expressions; if *A* |
| and *B* are both regular expressions, then *AB* is also a regular expression. |
| In general, if a string *p* matches *A* and another string *q* matches *B*, the |
| string *pq* will match AB. This holds unless *A* or *B* contain low precedence |
| operations; boundary conditions between *A* and *B*; or have numbered group |
| references. Thus, complex expressions can easily be constructed from simpler |
| primitive expressions like the ones described here. For details of the theory |
| and implementation of regular expressions, consult the Friedl book referenced |
| above, or almost any textbook about compiler construction. |
| |
| A brief explanation of the format of regular expressions follows. For further |
| information and a gentler presentation, consult the :ref:`regex-howto`. |
| |
| Regular expressions can contain both special and ordinary characters. Most |
| ordinary characters, like ``'A'``, ``'a'``, or ``'0'``, are the simplest regular |
| expressions; they simply match themselves. You can concatenate ordinary |
| characters, so ``last`` matches the string ``'last'``. (In the rest of this |
| section, we'll write RE's in ``this special style``, usually without quotes, and |
| strings to be matched ``'in single quotes'``.) |
| |
| Some characters, like ``'|'`` or ``'('``, are special. Special |
| characters either stand for classes of ordinary characters, or affect |
| how the regular expressions around them are interpreted. Regular |
| expression pattern strings may not contain null bytes, but can specify |
| the null byte using the ``\number`` notation, e.g., ``'\x00'``. |
| |
| |
| The special characters are: |
| |
| ``'.'`` |
| (Dot.) In the default mode, this matches any character except a newline. If |
| the :const:`DOTALL` flag has been specified, this matches any character |
| including a newline. |
| |
| ``'^'`` |
| (Caret.) Matches the start of the string, and in :const:`MULTILINE` mode also |
| matches immediately after each newline. |
| |
| ``'$'`` |
| Matches the end of the string or just before the newline at the end of the |
| string, and in :const:`MULTILINE` mode also matches before a newline. ``foo`` |
| matches both 'foo' and 'foobar', while the regular expression ``foo$`` matches |
| only 'foo'. More interestingly, searching for ``foo.$`` in ``'foo1\nfoo2\n'`` |
| matches 'foo2' normally, but 'foo1' in :const:`MULTILINE` mode; searching for |
| a single ``$`` in ``'foo\n'`` will find two (empty) matches: one just before |
| the newline, and one at the end of the string. |
| |
| ``'*'`` |
| Causes the resulting RE to match 0 or more repetitions of the preceding RE, as |
| many repetitions as are possible. ``ab*`` will match 'a', 'ab', or 'a' followed |
| by any number of 'b's. |
| |
| ``'+'`` |
| Causes the resulting RE to match 1 or more repetitions of the preceding RE. |
| ``ab+`` will match 'a' followed by any non-zero number of 'b's; it will not |
| match just 'a'. |
| |
| ``'?'`` |
| Causes the resulting RE to match 0 or 1 repetitions of the preceding RE. |
| ``ab?`` will match either 'a' or 'ab'. |
| |
| ``*?``, ``+?``, ``??`` |
| The ``'*'``, ``'+'``, and ``'?'`` qualifiers are all :dfn:`greedy`; they match |
| as much text as possible. Sometimes this behaviour isn't desired; if the RE |
| ``<.*>`` is matched against ``'<H1>title</H1>'``, it will match the entire |
| string, and not just ``'<H1>'``. Adding ``'?'`` after the qualifier makes it |
| perform the match in :dfn:`non-greedy` or :dfn:`minimal` fashion; as *few* |
| characters as possible will be matched. Using ``.*?`` in the previous |
| expression will match only ``'<H1>'``. |
| |
| ``{m}`` |
| Specifies that exactly *m* copies of the previous RE should be matched; fewer |
| matches cause the entire RE not to match. For example, ``a{6}`` will match |
| exactly six ``'a'`` characters, but not five. |
| |
| ``{m,n}`` |
| Causes the resulting RE to match from *m* to *n* repetitions of the preceding |
| RE, attempting to match as many repetitions as possible. For example, |
| ``a{3,5}`` will match from 3 to 5 ``'a'`` characters. Omitting *m* specifies a |
| lower bound of zero, and omitting *n* specifies an infinite upper bound. As an |
| example, ``a{4,}b`` will match ``aaaab`` or a thousand ``'a'`` characters |
| followed by a ``b``, but not ``aaab``. The comma may not be omitted or the |
| modifier would be confused with the previously described form. |
| |
| ``{m,n}?`` |
| Causes the resulting RE to match from *m* to *n* repetitions of the preceding |
| RE, attempting to match as *few* repetitions as possible. This is the |
| non-greedy version of the previous qualifier. For example, on the |
| 6-character string ``'aaaaaa'``, ``a{3,5}`` will match 5 ``'a'`` characters, |
| while ``a{3,5}?`` will only match 3 characters. |
| |
| ``'\'`` |
| Either escapes special characters (permitting you to match characters like |
| ``'*'``, ``'?'``, and so forth), or signals a special sequence; special |
| sequences are discussed below. |
| |
| If you're not using a raw string to express the pattern, remember that Python |
| also uses the backslash as an escape sequence in string literals; if the escape |
| sequence isn't recognized by Python's parser, the backslash and subsequent |
| character are included in the resulting string. However, if Python would |
| recognize the resulting sequence, the backslash should be repeated twice. This |
| is complicated and hard to understand, so it's highly recommended that you use |
| raw strings for all but the simplest expressions. |
| |
| ``[]`` |
| Used to indicate a set of characters. Characters can be listed individually, or |
| a range of characters can be indicated by giving two characters and separating |
| them by a ``'-'``. Special characters are not active inside sets. For example, |
| ``[akm$]`` will match any of the characters ``'a'``, ``'k'``, |
| ``'m'``, or ``'$'``; ``[a-z]`` will match any lowercase letter, and |
| ``[a-zA-Z0-9]`` matches any letter or digit. Character classes such |
| as ``\w`` or ``\S`` (defined below) are also acceptable inside a |
| range, although the characters they match depends on whether |
| :const:`ASCII` or :const:`LOCALE` mode is in force. If you want to |
| include a ``']'`` or a ``'-'`` inside a set, precede it with a |
| backslash, or place it as the first character. The pattern ``[]]`` |
| will match ``']'``, for example. |
| |
| You can match the characters not within a range by :dfn:`complementing` the set. |
| This is indicated by including a ``'^'`` as the first character of the set; |
| ``'^'`` elsewhere will simply match the ``'^'`` character. For example, |
| ``[^5]`` will match any character except ``'5'``, and ``[^^]`` will match any |
| character except ``'^'``. |
| |
| Note that inside ``[]`` the special forms and special characters lose |
| their meanings and only the syntaxes described here are valid. For |
| example, ``+``, ``*``, ``(``, ``)``, and so on are treated as |
| literals inside ``[]``, and backreferences cannot be used inside |
| ``[]``. |
| |
| ``'|'`` |
| ``A|B``, where A and B can be arbitrary REs, creates a regular expression that |
| will match either A or B. An arbitrary number of REs can be separated by the |
| ``'|'`` in this way. This can be used inside groups (see below) as well. As |
| the target string is scanned, REs separated by ``'|'`` are tried from left to |
| right. When one pattern completely matches, that branch is accepted. This means |
| that once ``A`` matches, ``B`` will not be tested further, even if it would |
| produce a longer overall match. In other words, the ``'|'`` operator is never |
| greedy. To match a literal ``'|'``, use ``\|``, or enclose it inside a |
| character class, as in ``[|]``. |
| |
| ``(...)`` |
| Matches whatever regular expression is inside the parentheses, and indicates the |
| start and end of a group; the contents of a group can be retrieved after a match |
| has been performed, and can be matched later in the string with the ``\number`` |
| special sequence, described below. To match the literals ``'('`` or ``')'``, |
| use ``\(`` or ``\)``, or enclose them inside a character class: ``[(] [)]``. |
| |
| ``(?...)`` |
| This is an extension notation (a ``'?'`` following a ``'('`` is not meaningful |
| otherwise). The first character after the ``'?'`` determines what the meaning |
| and further syntax of the construct is. Extensions usually do not create a new |
| group; ``(?P<name>...)`` is the only exception to this rule. Following are the |
| currently supported extensions. |
| |
| ``(?aiLmsux)`` |
| (One or more letters from the set ``'a'``, ``'i'``, ``'L'``, ``'m'``, |
| ``'s'``, ``'u'``, ``'x'``.) The group matches the empty string; the |
| letters set the corresponding flags: :const:`re.A` (ASCII-only matching), |
| :const:`re.I` (ignore case), :const:`re.L` (locale dependent), |
| :const:`re.M` (multi-line), :const:`re.S` (dot matches all), |
| and :const:`re.X` (verbose), for the entire regular expression. (The |
| flags are described in :ref:`contents-of-module-re`.) This |
| is useful if you wish to include the flags as part of the regular |
| expression, instead of passing a *flag* argument to the |
| :func:`re.compile` function. |
| |
| Note that the ``(?x)`` flag changes how the expression is parsed. It should be |
| used first in the expression string, or after one or more whitespace characters. |
| If there are non-whitespace characters before the flag, the results are |
| undefined. |
| |
| ``(?:...)`` |
| A non-grouping version of regular parentheses. Matches whatever regular |
| expression is inside the parentheses, but the substring matched by the group |
| *cannot* be retrieved after performing a match or referenced later in the |
| pattern. |
| |
| ``(?P<name>...)`` |
| Similar to regular parentheses, but the substring matched by the group is |
| accessible within the rest of the regular expression via the symbolic group |
| name *name*. Group names must be valid Python identifiers, and each group |
| name must be defined only once within a regular expression. A symbolic group |
| is also a numbered group, just as if the group were not named. So the group |
| named ``id`` in the example below can also be referenced as the numbered group |
| ``1``. |
| |
| For example, if the pattern is ``(?P<id>[a-zA-Z_]\w*)``, the group can be |
| referenced by its name in arguments to methods of match objects, such as |
| ``m.group('id')`` or ``m.end('id')``, and also by name in the regular |
| expression itself (using ``(?P=id)``) and replacement text given to |
| ``.sub()`` (using ``\g<id>``). |
| |
| ``(?P=name)`` |
| Matches whatever text was matched by the earlier group named *name*. |
| |
| ``(?#...)`` |
| A comment; the contents of the parentheses are simply ignored. |
| |
| ``(?=...)`` |
| Matches if ``...`` matches next, but doesn't consume any of the string. This is |
| called a lookahead assertion. For example, ``Isaac (?=Asimov)`` will match |
| ``'Isaac '`` only if it's followed by ``'Asimov'``. |
| |
| ``(?!...)`` |
| Matches if ``...`` doesn't match next. This is a negative lookahead assertion. |
| For example, ``Isaac (?!Asimov)`` will match ``'Isaac '`` only if it's *not* |
| followed by ``'Asimov'``. |
| |
| ``(?<=...)`` |
| Matches if the current position in the string is preceded by a match for ``...`` |
| that ends at the current position. This is called a :dfn:`positive lookbehind |
| assertion`. ``(?<=abc)def`` will find a match in ``abcdef``, since the |
| lookbehind will back up 3 characters and check if the contained pattern matches. |
| The contained pattern must only match strings of some fixed length, meaning that |
| ``abc`` or ``a|b`` are allowed, but ``a*`` and ``a{3,4}`` are not. Note that |
| patterns which start with positive lookbehind assertions will never match at the |
| beginning of the string being searched; you will most likely want to use the |
| :func:`search` function rather than the :func:`match` function: |
| |
| >>> import re |
| >>> m = re.search('(?<=abc)def', 'abcdef') |
| >>> m.group(0) |
| 'def' |
| |
| This example looks for a word following a hyphen: |
| |
| >>> m = re.search('(?<=-)\w+', 'spam-egg') |
| >>> m.group(0) |
| 'egg' |
| |
| ``(?<!...)`` |
| Matches if the current position in the string is not preceded by a match for |
| ``...``. This is called a :dfn:`negative lookbehind assertion`. Similar to |
| positive lookbehind assertions, the contained pattern must only match strings of |
| some fixed length. Patterns which start with negative lookbehind assertions may |
| match at the beginning of the string being searched. |
| |
| ``(?(id/name)yes-pattern|no-pattern)`` |
| Will try to match with ``yes-pattern`` if the group with given *id* or *name* |
| exists, and with ``no-pattern`` if it doesn't. ``no-pattern`` is optional and |
| can be omitted. For example, ``(<)?(\w+@\w+(?:\.\w+)+)(?(1)>)`` is a poor email |
| matching pattern, which will match with ``'<user@host.com>'`` as well as |
| ``'user@host.com'``, but not with ``'<user@host.com'``. |
| |
| |
| The special sequences consist of ``'\'`` and a character from the list below. |
| If the ordinary character is not on the list, then the resulting RE will match |
| the second character. For example, ``\$`` matches the character ``'$'``. |
| |
| ``\number`` |
| Matches the contents of the group of the same number. Groups are numbered |
| starting from 1. For example, ``(.+) \1`` matches ``'the the'`` or ``'55 55'``, |
| but not ``'the end'`` (note the space after the group). This special sequence |
| can only be used to match one of the first 99 groups. If the first digit of |
| *number* is 0, or *number* is 3 octal digits long, it will not be interpreted as |
| a group match, but as the character with octal value *number*. Inside the |
| ``'['`` and ``']'`` of a character class, all numeric escapes are treated as |
| characters. |
| |
| ``\A`` |
| Matches only at the start of the string. |
| |
| ``\b`` |
| Matches the empty string, but only at the beginning or end of a word. |
| A word is defined as a sequence of Unicode alphanumeric or underscore |
| characters, so the end of a word is indicated by whitespace or a |
| non-alphanumeric, non-underscore Unicode character. Note that |
| formally, ``\b`` is defined as the boundary between a ``\w`` and a |
| ``\W`` character (or vice versa). By default Unicode alphanumerics |
| are the ones used, but this can be changed by using the :const:`ASCII` |
| flag. Inside a character range, ``\b`` represents the backspace |
| character, for compatibility with Python's string literals. |
| |
| ``\B`` |
| Matches the empty string, but only when it is *not* at the beginning or end of a |
| word. This is just the opposite of ``\b``, so word characters are |
| Unicode alphanumerics or the underscore, although this can be changed |
| by using the :const:`ASCII` flag. |
| |
| ``\d`` |
| For Unicode (str) patterns: |
| Matches any Unicode decimal digit (that is, any character in |
| Unicode character category [Nd]). This includes ``[0-9]``, and |
| also many other digit characters. If the :const:`ASCII` flag is |
| used only ``[0-9]`` is matched (but the flag affects the entire |
| regular expression, so in such cases using an explicit ``[0-9]`` |
| may be a better choice). |
| For 8-bit (bytes) patterns: |
| Matches any decimal digit; this is equivalent to ``[0-9]``. |
| |
| ``\D`` |
| Matches any character which is not a Unicode decimal digit. This is |
| the opposite of ``\d``. If the :const:`ASCII` flag is used this |
| becomes the equivalent of ``[^0-9]`` (but the flag affects the entire |
| regular expression, so in such cases using an explicit ``[^0-9]`` may |
| be a better choice). |
| |
| ``\s`` |
| For Unicode (str) patterns: |
| Matches Unicode whitespace characters (which includes |
| ``[ \t\n\r\f\v]``, and also many other characters, for example the |
| non-breaking spaces mandated by typography rules in many |
| languages). If the :const:`ASCII` flag is used, only |
| ``[ \t\n\r\f\v]`` is matched (but the flag affects the entire |
| regular expression, so in such cases using an explicit |
| ``[ \t\n\r\f\v]`` may be a better choice). |
| |
| For 8-bit (bytes) patterns: |
| Matches characters considered whitespace in the ASCII character set; |
| this is equivalent to ``[ \t\n\r\f\v]``. |
| |
| ``\S`` |
| Matches any character which is not a Unicode whitespace character. This is |
| the opposite of ``\s``. If the :const:`ASCII` flag is used this |
| becomes the equivalent of ``[^ \t\n\r\f\v]`` (but the flag affects the entire |
| regular expression, so in such cases using an explicit ``[^ \t\n\r\f\v]`` may |
| be a better choice). |
| |
| ``\w`` |
| For Unicode (str) patterns: |
| Matches Unicode word characters; this includes most characters |
| that can be part of a word in any language, as well as numbers and |
| the underscore. If the :const:`ASCII` flag is used, only |
| ``[a-zA-Z0-9_]`` is matched (but the flag affects the entire |
| regular expression, so in such cases using an explicit |
| ``[a-zA-Z0-9_]`` may be a better choice). |
| For 8-bit (bytes) patterns: |
| Matches characters considered alphanumeric in the ASCII character set; |
| this is equivalent to ``[a-zA-Z0-9_]``. |
| |
| ``\W`` |
| Matches any character which is not a Unicode word character. This is |
| the opposite of ``\w``. If the :const:`ASCII` flag is used this |
| becomes the equivalent of ``[^a-zA-Z0-9_]`` (but the flag affects the |
| entire regular expression, so in such cases using an explicit |
| ``[^a-zA-Z0-9_]`` may be a better choice). |
| |
| ``\Z`` |
| Matches only at the end of the string. |
| |
| Most of the standard escapes supported by Python string literals are also |
| accepted by the regular expression parser:: |
| |
| \a \b \f \n |
| \r \t \v \x |
| \\ |
| |
| Octal escapes are included in a limited form: If the first digit is a 0, or if |
| there are three octal digits, it is considered an octal escape. Otherwise, it is |
| a group reference. As for string literals, octal escapes are always at most |
| three digits in length. |
| |
| |
| .. _matching-searching: |
| |
| Matching vs Searching |
| --------------------- |
| |
| .. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org> |
| |
| |
| Python offers two different primitive operations based on regular expressions: |
| **match** checks for a match only at the beginning of the string, while |
| **search** checks for a match anywhere in the string (this is what Perl does |
| by default). |
| |
| Note that match may differ from search even when using a regular expression |
| beginning with ``'^'``: ``'^'`` matches only at the start of the string, or in |
| :const:`MULTILINE` mode also immediately following a newline. The "match" |
| operation succeeds only if the pattern matches at the start of the string |
| regardless of mode, or at the starting position given by the optional *pos* |
| argument regardless of whether a newline precedes it. |
| |
| >>> re.match("c", "abcdef") # No match |
| >>> re.search("c", "abcdef") # Match |
| <_sre.SRE_Match object at ...> |
| |
| |
| .. _contents-of-module-re: |
| |
| Module Contents |
| --------------- |
| |
| The module defines several functions, constants, and an exception. Some of the |
| functions are simplified versions of the full featured methods for compiled |
| regular expressions. Most non-trivial applications always use the compiled |
| form. |
| |
| |
| .. function:: compile(pattern, flags=0) |
| |
| Compile a regular expression pattern into a regular expression object, which |
| can be used for matching using its :func:`match` and :func:`search` methods, |
| described below. |
| |
| The expression's behaviour can be modified by specifying a *flags* value. |
| Values can be any of the following variables, combined using bitwise OR (the |
| ``|`` operator). |
| |
| The sequence :: |
| |
| prog = re.compile(pattern) |
| result = prog.match(string) |
| |
| is equivalent to :: |
| |
| result = re.match(pattern, string) |
| |
| but using :func:`re.compile` and saving the resulting regular expression |
| object for reuse is more efficient when the expression will be used several |
| times in a single program. |
| |
| .. note:: |
| |
| The compiled versions of the most recent patterns passed to |
| :func:`re.match`, :func:`re.search` or :func:`re.compile` are cached, so |
| programs that use only a few regular expressions at a time needn't worry |
| about compiling regular expressions. |
| |
| |
| .. data:: A |
| ASCII |
| |
| Make ``\w``, ``\W``, ``\b``, ``\B``, ``\d``, ``\D``, ``\s`` and ``\S`` |
| perform ASCII-only matching instead of full Unicode matching. This is only |
| meaningful for Unicode patterns, and is ignored for byte patterns. |
| |
| Note that for backward compatibility, the :const:`re.U` flag still |
| exists (as well as its synonym :const:`re.UNICODE` and its embedded |
| counterpart ``(?u)``), but these are redundant in Python 3 since |
| matches are Unicode by default for strings (and Unicode matching |
| isn't allowed for bytes). |
| |
| |
| .. data:: I |
| IGNORECASE |
| |
| Perform case-insensitive matching; expressions like ``[A-Z]`` will match |
| lowercase letters, too. This is not affected by the current locale |
| and works for Unicode characters as expected. |
| |
| |
| .. data:: L |
| LOCALE |
| |
| Make ``\w``, ``\W``, ``\b``, ``\B``, ``\s`` and ``\S`` dependent on the |
| current locale. The use of this flag is discouraged as the locale mechanism |
| is very unreliable, and it only handles one "culture" at a time anyway; |
| you should use Unicode matching instead, which is the default in Python 3 |
| for Unicode (str) patterns. |
| |
| |
| .. data:: M |
| MULTILINE |
| |
| When specified, the pattern character ``'^'`` matches at the beginning of the |
| string and at the beginning of each line (immediately following each newline); |
| and the pattern character ``'$'`` matches at the end of the string and at the |
| end of each line (immediately preceding each newline). By default, ``'^'`` |
| matches only at the beginning of the string, and ``'$'`` only at the end of the |
| string and immediately before the newline (if any) at the end of the string. |
| |
| |
| .. data:: S |
| DOTALL |
| |
| Make the ``'.'`` special character match any character at all, including a |
| newline; without this flag, ``'.'`` will match anything *except* a newline. |
| |
| |
| .. data:: X |
| VERBOSE |
| |
| This flag allows you to write regular expressions that look nicer. Whitespace |
| within the pattern is ignored, except when in a character class or preceded by |
| an unescaped backslash, and, when a line contains a ``'#'`` neither in a |
| character class or preceded by an unescaped backslash, all characters from the |
| leftmost such ``'#'`` through the end of the line are ignored. |
| |
| That means that the two following regular expression objects that match a |
| decimal number are functionally equal:: |
| |
| a = re.compile(r"""\d + # the integral part |
| \. # the decimal point |
| \d * # some fractional digits""", re.X) |
| b = re.compile(r"\d+\.\d*") |
| |
| |
| |
| |
| .. function:: search(pattern, string, flags=0) |
| |
| Scan through *string* looking for a location where the regular expression |
| *pattern* produces a match, and return a corresponding :ref:`match object |
| <match-objects>`. Return ``None`` if no position in the string matches the |
| pattern; note that this is different from finding a zero-length match at some |
| point in the string. |
| |
| |
| .. function:: match(pattern, string, flags=0) |
| |
| If zero or more characters at the beginning of *string* match the regular |
| expression *pattern*, return a corresponding :ref:`match object |
| <match-objects>`. Return ``None`` if the string does not match the pattern; |
| note that this is different from a zero-length match. |
| |
| .. note:: |
| |
| If you want to locate a match anywhere in *string*, use :func:`search` |
| instead. |
| |
| |
| .. function:: split(pattern, string, maxsplit=0, flags=0) |
| |
| Split *string* by the occurrences of *pattern*. If capturing parentheses are |
| used in *pattern*, then the text of all groups in the pattern are also returned |
| as part of the resulting list. If *maxsplit* is nonzero, at most *maxsplit* |
| splits occur, and the remainder of the string is returned as the final element |
| of the list. :: |
| |
| >>> re.split('\W+', 'Words, words, words.') |
| ['Words', 'words', 'words', ''] |
| >>> re.split('(\W+)', 'Words, words, words.') |
| ['Words', ', ', 'words', ', ', 'words', '.', ''] |
| >>> re.split('\W+', 'Words, words, words.', 1) |
| ['Words', 'words, words.'] |
| >>> re.split('[a-f]+', '0a3B9', flags=re.IGNORECASE) |
| ['0', '3', '9'] |
| |
| If there are capturing groups in the separator and it matches at the start of |
| the string, the result will start with an empty string. The same holds for |
| the end of the string: |
| |
| >>> re.split('(\W+)', '...words, words...') |
| ['', '...', 'words', ', ', 'words', '...', ''] |
| |
| That way, separator components are always found at the same relative |
| indices within the result list (e.g., if there's one capturing group |
| in the separator, the 0th, the 2nd and so forth). |
| |
| Note that *split* will never split a string on an empty pattern match. |
| For example: |
| |
| >>> re.split('x*', 'foo') |
| ['foo'] |
| >>> re.split("(?m)^$", "foo\n\nbar\n") |
| ['foo\n\nbar\n'] |
| |
| .. versionchanged:: 3.1 |
| Added the optional flags argument. |
| |
| |
| .. function:: findall(pattern, string, flags=0) |
| |
| Return all non-overlapping matches of *pattern* in *string*, as a list of |
| strings. The *string* is scanned left-to-right, and matches are returned in |
| the order found. If one or more groups are present in the pattern, return a |
| list of groups; this will be a list of tuples if the pattern has more than |
| one group. Empty matches are included in the result unless they touch the |
| beginning of another match. |
| |
| |
| .. function:: finditer(pattern, string, flags=0) |
| |
| Return an :term:`iterator` yielding :ref:`match objects <match-objects>` over |
| all non-overlapping matches for the RE *pattern* in *string*. The *string* |
| is scanned left-to-right, and matches are returned in the order found. Empty |
| matches are included in the result unless they touch the beginning of another |
| match. |
| |
| |
| .. function:: sub(pattern, repl, string, count=0, flags=0) |
| |
| Return the string obtained by replacing the leftmost non-overlapping occurrences |
| of *pattern* in *string* by the replacement *repl*. If the pattern isn't found, |
| *string* is returned unchanged. *repl* can be a string or a function; if it is |
| a string, any backslash escapes in it are processed. That is, ``\n`` is |
| converted to a single newline character, ``\r`` is converted to a linefeed, and |
| so forth. Unknown escapes such as ``\j`` are left alone. Backreferences, such |
| as ``\6``, are replaced with the substring matched by group 6 in the pattern. |
| For example: |
| |
| >>> re.sub(r'def\s+([a-zA-Z_][a-zA-Z_0-9]*)\s*\(\s*\):', |
| ... r'static PyObject*\npy_\1(void)\n{', |
| ... 'def myfunc():') |
| 'static PyObject*\npy_myfunc(void)\n{' |
| |
| If *repl* is a function, it is called for every non-overlapping occurrence of |
| *pattern*. The function takes a single match object argument, and returns the |
| replacement string. For example: |
| |
| >>> def dashrepl(matchobj): |
| ... if matchobj.group(0) == '-': return ' ' |
| ... else: return '-' |
| >>> re.sub('-{1,2}', dashrepl, 'pro----gram-files') |
| 'pro--gram files' |
| >>> re.sub(r'\sAND\s', ' & ', 'Baked Beans And Spam', flags=re.IGNORECASE) |
| 'Baked Beans & Spam' |
| |
| The pattern may be a string or an RE object. |
| |
| The optional argument *count* is the maximum number of pattern occurrences to be |
| replaced; *count* must be a non-negative integer. If omitted or zero, all |
| occurrences will be replaced. Empty matches for the pattern are replaced only |
| when not adjacent to a previous match, so ``sub('x*', '-', 'abc')`` returns |
| ``'-a-b-c-'``. |
| |
| In addition to character escapes and backreferences as described above, |
| ``\g<name>`` will use the substring matched by the group named ``name``, as |
| defined by the ``(?P<name>...)`` syntax. ``\g<number>`` uses the corresponding |
| group number; ``\g<2>`` is therefore equivalent to ``\2``, but isn't ambiguous |
| in a replacement such as ``\g<2>0``. ``\20`` would be interpreted as a |
| reference to group 20, not a reference to group 2 followed by the literal |
| character ``'0'``. The backreference ``\g<0>`` substitutes in the entire |
| substring matched by the RE. |
| |
| .. versionchanged:: 3.1 |
| Added the optional flags argument. |
| |
| |
| .. function:: subn(pattern, repl, string, count=0, flags=0) |
| |
| Perform the same operation as :func:`sub`, but return a tuple ``(new_string, |
| number_of_subs_made)``. |
| |
| .. versionchanged:: 3.1 |
| Added the optional flags argument. |
| |
| |
| .. function:: escape(string) |
| |
| Return *string* with all non-alphanumerics backslashed; this is useful if you |
| want to match an arbitrary literal string that may have regular expression |
| metacharacters in it. |
| |
| |
| .. function:: purge() |
| |
| Clear the regular expression cache. |
| |
| |
| .. exception:: error |
| |
| Exception raised when a string passed to one of the functions here is not a |
| valid regular expression (for example, it might contain unmatched parentheses) |
| or when some other error occurs during compilation or matching. It is never an |
| error if a string contains no match for a pattern. |
| |
| |
| .. _re-objects: |
| |
| Regular Expression Objects |
| -------------------------- |
| |
| Compiled regular expression objects support the following methods and |
| attributes. |
| |
| .. method:: regex.search(string[, pos[, endpos]]) |
| |
| Scan through *string* looking for a location where this regular expression |
| produces a match, and return a corresponding :ref:`match object |
| <match-objects>`. Return ``None`` if no position in the string matches the |
| pattern; note that this is different from finding a zero-length match at some |
| point in the string. |
| |
| The optional second parameter *pos* gives an index in the string where the |
| search is to start; it defaults to ``0``. This is not completely equivalent to |
| slicing the string; the ``'^'`` pattern character matches at the real beginning |
| of the string and at positions just after a newline, but not necessarily at the |
| index where the search is to start. |
| |
| The optional parameter *endpos* limits how far the string will be searched; it |
| will be as if the string is *endpos* characters long, so only the characters |
| from *pos* to ``endpos - 1`` will be searched for a match. If *endpos* is less |
| than *pos*, no match will be found, otherwise, if *rx* is a compiled regular |
| expression object, ``rx.search(string, 0, 50)`` is equivalent to |
| ``rx.search(string[:50], 0)``. |
| |
| >>> pattern = re.compile("d") |
| >>> pattern.search("dog") # Match at index 0 |
| <_sre.SRE_Match object at ...> |
| >>> pattern.search("dog", 1) # No match; search doesn't include the "d" |
| |
| |
| .. method:: regex.match(string[, pos[, endpos]]) |
| |
| If zero or more characters at the *beginning* of *string* match this regular |
| expression, return a corresponding :ref:`match object <match-objects>`. |
| Return ``None`` if the string does not match the pattern; note that this is |
| different from a zero-length match. |
| |
| The optional *pos* and *endpos* parameters have the same meaning as for the |
| :meth:`~regex.search` method. |
| |
| .. note:: |
| |
| If you want to locate a match anywhere in *string*, use |
| :meth:`~regex.search` instead. |
| |
| >>> pattern = re.compile("o") |
| >>> pattern.match("dog") # No match as "o" is not at the start of "dog". |
| >>> pattern.match("dog", 1) # Match as "o" is the 2nd character of "dog". |
| <_sre.SRE_Match object at ...> |
| |
| |
| .. method:: regex.split(string, maxsplit=0) |
| |
| Identical to the :func:`split` function, using the compiled pattern. |
| |
| |
| .. method:: regex.findall(string[, pos[, endpos]]) |
| |
| Similar to the :func:`findall` function, using the compiled pattern, but |
| also accepts optional *pos* and *endpos* parameters that limit the search |
| region like for :meth:`match`. |
| |
| |
| .. method:: regex.finditer(string[, pos[, endpos]]) |
| |
| Similar to the :func:`finditer` function, using the compiled pattern, but |
| also accepts optional *pos* and *endpos* parameters that limit the search |
| region like for :meth:`match`. |
| |
| |
| .. method:: regex.sub(repl, string, count=0) |
| |
| Identical to the :func:`sub` function, using the compiled pattern. |
| |
| |
| .. method:: regex.subn(repl, string, count=0) |
| |
| Identical to the :func:`subn` function, using the compiled pattern. |
| |
| |
| .. attribute:: regex.flags |
| |
| The flags argument used when the RE object was compiled, or ``0`` if no flags |
| were provided. |
| |
| |
| .. attribute:: regex.groups |
| |
| The number of capturing groups in the pattern. |
| |
| |
| .. attribute:: regex.groupindex |
| |
| A dictionary mapping any symbolic group names defined by ``(?P<id>)`` to group |
| numbers. The dictionary is empty if no symbolic groups were used in the |
| pattern. |
| |
| |
| .. attribute:: regex.pattern |
| |
| The pattern string from which the RE object was compiled. |
| |
| |
| .. _match-objects: |
| |
| Match Objects |
| ------------- |
| |
| Match objects always have a boolean value of :const:`True`, so that you can test |
| whether e.g. :func:`match` resulted in a match with a simple if statement. They |
| support the following methods and attributes: |
| |
| |
| .. method:: match.expand(template) |
| |
| Return the string obtained by doing backslash substitution on the template |
| string *template*, as done by the :meth:`~regex.sub` method. |
| Escapes such as ``\n`` are converted to the appropriate characters, |
| and numeric backreferences (``\1``, ``\2``) and named backreferences |
| (``\g<1>``, ``\g<name>``) are replaced by the contents of the |
| corresponding group. |
| |
| |
| .. method:: match.group([group1, ...]) |
| |
| Returns one or more subgroups of the match. If there is a single argument, the |
| result is a single string; if there are multiple arguments, the result is a |
| tuple with one item per argument. Without arguments, *group1* defaults to zero |
| (the whole match is returned). If a *groupN* argument is zero, the corresponding |
| return value is the entire matching string; if it is in the inclusive range |
| [1..99], it is the string matching the corresponding parenthesized group. If a |
| group number is negative or larger than the number of groups defined in the |
| pattern, an :exc:`IndexError` exception is raised. If a group is contained in a |
| part of the pattern that did not match, the corresponding result is ``None``. |
| If a group is contained in a part of the pattern that matched multiple times, |
| the last match is returned. |
| |
| >>> m = re.match(r"(\w+) (\w+)", "Isaac Newton, physicist") |
| >>> m.group(0) # The entire match |
| 'Isaac Newton' |
| >>> m.group(1) # The first parenthesized subgroup. |
| 'Isaac' |
| >>> m.group(2) # The second parenthesized subgroup. |
| 'Newton' |
| >>> m.group(1, 2) # Multiple arguments give us a tuple. |
| ('Isaac', 'Newton') |
| |
| If the regular expression uses the ``(?P<name>...)`` syntax, the *groupN* |
| arguments may also be strings identifying groups by their group name. If a |
| string argument is not used as a group name in the pattern, an :exc:`IndexError` |
| exception is raised. |
| |
| A moderately complicated example: |
| |
| >>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcolm Reynolds") |
| >>> m.group('first_name') |
| 'Malcolm' |
| >>> m.group('last_name') |
| 'Reynolds' |
| |
| Named groups can also be referred to by their index: |
| |
| >>> m.group(1) |
| 'Malcolm' |
| >>> m.group(2) |
| 'Reynolds' |
| |
| If a group matches multiple times, only the last match is accessible: |
| |
| >>> m = re.match(r"(..)+", "a1b2c3") # Matches 3 times. |
| >>> m.group(1) # Returns only the last match. |
| 'c3' |
| |
| |
| .. method:: match.groups(default=None) |
| |
| Return a tuple containing all the subgroups of the match, from 1 up to however |
| many groups are in the pattern. The *default* argument is used for groups that |
| did not participate in the match; it defaults to ``None``. |
| |
| For example: |
| |
| >>> m = re.match(r"(\d+)\.(\d+)", "24.1632") |
| >>> m.groups() |
| ('24', '1632') |
| |
| If we make the decimal place and everything after it optional, not all groups |
| might participate in the match. These groups will default to ``None`` unless |
| the *default* argument is given: |
| |
| >>> m = re.match(r"(\d+)\.?(\d+)?", "24") |
| >>> m.groups() # Second group defaults to None. |
| ('24', None) |
| >>> m.groups('0') # Now, the second group defaults to '0'. |
| ('24', '0') |
| |
| |
| .. method:: match.groupdict(default=None) |
| |
| Return a dictionary containing all the *named* subgroups of the match, keyed by |
| the subgroup name. The *default* argument is used for groups that did not |
| participate in the match; it defaults to ``None``. For example: |
| |
| >>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcolm Reynolds") |
| >>> m.groupdict() |
| {'first_name': 'Malcolm', 'last_name': 'Reynolds'} |
| |
| |
| .. method:: match.start([group]) |
| match.end([group]) |
| |
| Return the indices of the start and end of the substring matched by *group*; |
| *group* defaults to zero (meaning the whole matched substring). Return ``-1`` if |
| *group* exists but did not contribute to the match. For a match object *m*, and |
| a group *g* that did contribute to the match, the substring matched by group *g* |
| (equivalent to ``m.group(g)``) is :: |
| |
| m.string[m.start(g):m.end(g)] |
| |
| Note that ``m.start(group)`` will equal ``m.end(group)`` if *group* matched a |
| null string. For example, after ``m = re.search('b(c?)', 'cba')``, |
| ``m.start(0)`` is 1, ``m.end(0)`` is 2, ``m.start(1)`` and ``m.end(1)`` are both |
| 2, and ``m.start(2)`` raises an :exc:`IndexError` exception. |
| |
| An example that will remove *remove_this* from email addresses: |
| |
| >>> email = "tony@tiremove_thisger.net" |
| >>> m = re.search("remove_this", email) |
| >>> email[:m.start()] + email[m.end():] |
| 'tony@tiger.net' |
| |
| |
| .. method:: match.span([group]) |
| |
| For a match *m*, return the 2-tuple ``(m.start(group), m.end(group))``. Note |
| that if *group* did not contribute to the match, this is ``(-1, -1)``. |
| *group* defaults to zero, the entire match. |
| |
| |
| .. attribute:: match.pos |
| |
| The value of *pos* which was passed to the :meth:`~regex.search` or |
| :meth:`~regex.match` method of a :ref:`match object <match-objects>`. This |
| is the index into the string at which the RE engine started looking for a |
| match. |
| |
| |
| .. attribute:: match.endpos |
| |
| The value of *endpos* which was passed to the :meth:`~regex.search` or |
| :meth:`~regex.match` method of a :ref:`match object <match-objects>`. This |
| is the index into the string beyond which the RE engine will not go. |
| |
| |
| .. attribute:: match.lastindex |
| |
| The integer index of the last matched capturing group, or ``None`` if no group |
| was matched at all. For example, the expressions ``(a)b``, ``((a)(b))``, and |
| ``((ab))`` will have ``lastindex == 1`` if applied to the string ``'ab'``, while |
| the expression ``(a)(b)`` will have ``lastindex == 2``, if applied to the same |
| string. |
| |
| |
| .. attribute:: match.lastgroup |
| |
| The name of the last matched capturing group, or ``None`` if the group didn't |
| have a name, or if no group was matched at all. |
| |
| |
| .. attribute:: match.re |
| |
| The regular expression object whose :meth:`~regex.match` or |
| :meth:`~regex.search` method produced this match instance. |
| |
| |
| .. attribute:: match.string |
| |
| The string passed to :meth:`~regex.match` or :meth:`~regex.search`. |
| |
| |
| Examples |
| -------- |
| |
| |
| Checking For a Pair |
| ^^^^^^^^^^^^^^^^^^^ |
| |
| In this example, we'll use the following helper function to display match |
| objects a little more gracefully: |
| |
| .. testcode:: |
| |
| def displaymatch(match): |
| if match is None: |
| return None |
| return '<Match: %r, groups=%r>' % (match.group(), match.groups()) |
| |
| Suppose you are writing a poker program where a player's hand is represented as |
| a 5-character string with each character representing a card, "a" for ace, "k" |
| for king, "q" for queen, j for jack, "0" for 10, and "1" through "9" |
| representing the card with that value. |
| |
| To see if a given string is a valid hand, one could do the following: |
| |
| >>> valid = re.compile(r"[0-9akqj]{5}$") |
| >>> displaymatch(valid.match("ak05q")) # Valid. |
| "<Match: 'ak05q', groups=()>" |
| >>> displaymatch(valid.match("ak05e")) # Invalid. |
| >>> displaymatch(valid.match("ak0")) # Invalid. |
| >>> displaymatch(valid.match("727ak")) # Valid. |
| "<Match: '727ak', groups=()>" |
| |
| That last hand, ``"727ak"``, contained a pair, or two of the same valued cards. |
| To match this with a regular expression, one could use backreferences as such: |
| |
| >>> pair = re.compile(r".*(.).*\1") |
| >>> displaymatch(pair.match("717ak")) # Pair of 7s. |
| "<Match: '717', groups=('7',)>" |
| >>> displaymatch(pair.match("718ak")) # No pairs. |
| >>> displaymatch(pair.match("354aa")) # Pair of aces. |
| "<Match: '354aa', groups=('a',)>" |
| |
| To find out what card the pair consists of, one could use the |
| :meth:`~match.group` method of the match object in the following manner: |
| |
| .. doctest:: |
| |
| >>> pair.match("717ak").group(1) |
| '7' |
| |
| # Error because re.match() returns None, which doesn't have a group() method: |
| >>> pair.match("718ak").group(1) |
| Traceback (most recent call last): |
| File "<pyshell#23>", line 1, in <module> |
| re.match(r".*(.).*\1", "718ak").group(1) |
| AttributeError: 'NoneType' object has no attribute 'group' |
| |
| >>> pair.match("354aa").group(1) |
| 'a' |
| |
| |
| Simulating scanf() |
| ^^^^^^^^^^^^^^^^^^ |
| |
| .. index:: single: scanf() |
| |
| Python does not currently have an equivalent to :cfunc:`scanf`. Regular |
| expressions are generally more powerful, though also more verbose, than |
| :cfunc:`scanf` format strings. The table below offers some more-or-less |
| equivalent mappings between :cfunc:`scanf` format tokens and regular |
| expressions. |
| |
| +--------------------------------+---------------------------------------------+ |
| | :cfunc:`scanf` Token | Regular Expression | |
| +================================+=============================================+ |
| | ``%c`` | ``.`` | |
| +--------------------------------+---------------------------------------------+ |
| | ``%5c`` | ``.{5}`` | |
| +--------------------------------+---------------------------------------------+ |
| | ``%d`` | ``[-+]?\d+`` | |
| +--------------------------------+---------------------------------------------+ |
| | ``%e``, ``%E``, ``%f``, ``%g`` | ``[-+]?(\d+(\.\d*)?|\.\d+)([eE][-+]?\d+)?`` | |
| +--------------------------------+---------------------------------------------+ |
| | ``%i`` | ``[-+]?(0[xX][\dA-Fa-f]+|0[0-7]*|\d+)`` | |
| +--------------------------------+---------------------------------------------+ |
| | ``%o`` | ``0[0-7]*`` | |
| +--------------------------------+---------------------------------------------+ |
| | ``%s`` | ``\S+`` | |
| +--------------------------------+---------------------------------------------+ |
| | ``%u`` | ``\d+`` | |
| +--------------------------------+---------------------------------------------+ |
| | ``%x``, ``%X`` | ``0[xX][\dA-Fa-f]+`` | |
| +--------------------------------+---------------------------------------------+ |
| |
| To extract the filename and numbers from a string like :: |
| |
| /usr/sbin/sendmail - 0 errors, 4 warnings |
| |
| you would use a :cfunc:`scanf` format like :: |
| |
| %s - %d errors, %d warnings |
| |
| The equivalent regular expression would be :: |
| |
| (\S+) - (\d+) errors, (\d+) warnings |
| |
| |
| Avoiding recursion |
| ^^^^^^^^^^^^^^^^^^ |
| |
| If you create regular expressions that require the engine to perform a lot of |
| recursion, you may encounter a :exc:`RuntimeError` exception with the message |
| ``maximum recursion limit`` exceeded. For example, :: |
| |
| >>> s = 'Begin ' + 1000*'a very long string ' + 'end' |
| >>> re.match('Begin (\w| )*? end', s).end() |
| Traceback (most recent call last): |
| File "<stdin>", line 1, in ? |
| File "/usr/local/lib/python3.2/re.py", line 132, in match |
| return _compile(pattern, flags).match(string) |
| RuntimeError: maximum recursion limit exceeded |
| |
| You can often restructure your regular expression to avoid recursion. |
| |
| Simple uses of the ``*?`` pattern are special-cased to avoid recursion. Thus, |
| the above regular expression can avoid recursion by being recast as ``Begin |
| [a-zA-Z0-9_ ]*?end``. As a further benefit, such regular expressions will run |
| faster than their recursive equivalents. |
| |
| |
| search() vs. match() |
| ^^^^^^^^^^^^^^^^^^^^ |
| |
| In a nutshell, :func:`match` only attempts to match a pattern at the beginning |
| of a string where :func:`search` will match a pattern anywhere in a string. |
| For example: |
| |
| >>> re.match("o", "dog") # No match as "o" is not the first letter of "dog". |
| >>> re.search("o", "dog") # Match as search() looks everywhere in the string. |
| <_sre.SRE_Match object at ...> |
| |
| .. note:: |
| |
| The following applies only to regular expression objects like those created |
| with ``re.compile("pattern")``, not the primitives ``re.match(pattern, |
| string)`` or ``re.search(pattern, string)``. |
| |
| :func:`match` has an optional second parameter that gives an index in the string |
| where the search is to start:: |
| |
| >>> pattern = re.compile("o") |
| >>> pattern.match("dog") # No match as "o" is not at the start of "dog." |
| |
| # Equivalent to the above expression as 0 is the default starting index: |
| >>> pattern.match("dog", 0) |
| |
| # Match as "o" is the 2nd character of "dog" (index 0 is the first): |
| >>> pattern.match("dog", 1) |
| <_sre.SRE_Match object at ...> |
| >>> pattern.match("dog", 2) # No match as "o" is not the 3rd character of "dog." |
| |
| |
| Making a Phonebook |
| ^^^^^^^^^^^^^^^^^^ |
| |
| :func:`split` splits a string into a list delimited by the passed pattern. The |
| method is invaluable for converting textual data into data structures that can be |
| easily read and modified by Python as demonstrated in the following example that |
| creates a phonebook. |
| |
| First, here is the input. Normally it may come from a file, here we are using |
| triple-quoted string syntax: |
| |
| >>> input = """Ross McFluff: 834.345.1254 155 Elm Street |
| ... |
| ... Ronald Heathmore: 892.345.3428 436 Finley Avenue |
| ... Frank Burger: 925.541.7625 662 South Dogwood Way |
| ... |
| ... |
| ... Heather Albrecht: 548.326.4584 919 Park Place""" |
| |
| The entries are separated by one or more newlines. Now we convert the string |
| into a list with each nonempty line having its own entry: |
| |
| .. doctest:: |
| :options: +NORMALIZE_WHITESPACE |
| |
| >>> entries = re.split("\n+", input) |
| >>> entries |
| ['Ross McFluff: 834.345.1254 155 Elm Street', |
| 'Ronald Heathmore: 892.345.3428 436 Finley Avenue', |
| 'Frank Burger: 925.541.7625 662 South Dogwood Way', |
| 'Heather Albrecht: 548.326.4584 919 Park Place'] |
| |
| Finally, split each entry into a list with first name, last name, telephone |
| number, and address. We use the ``maxsplit`` parameter of :func:`split` |
| because the address has spaces, our splitting pattern, in it: |
| |
| .. doctest:: |
| :options: +NORMALIZE_WHITESPACE |
| |
| >>> [re.split(":? ", entry, 3) for entry in entries] |
| [['Ross', 'McFluff', '834.345.1254', '155 Elm Street'], |
| ['Ronald', 'Heathmore', '892.345.3428', '436 Finley Avenue'], |
| ['Frank', 'Burger', '925.541.7625', '662 South Dogwood Way'], |
| ['Heather', 'Albrecht', '548.326.4584', '919 Park Place']] |
| |
| The ``:?`` pattern matches the colon after the last name, so that it does not |
| occur in the result list. With a ``maxsplit`` of ``4``, we could separate the |
| house number from the street name: |
| |
| .. doctest:: |
| :options: +NORMALIZE_WHITESPACE |
| |
| >>> [re.split(":? ", entry, 4) for entry in entries] |
| [['Ross', 'McFluff', '834.345.1254', '155', 'Elm Street'], |
| ['Ronald', 'Heathmore', '892.345.3428', '436', 'Finley Avenue'], |
| ['Frank', 'Burger', '925.541.7625', '662', 'South Dogwood Way'], |
| ['Heather', 'Albrecht', '548.326.4584', '919', 'Park Place']] |
| |
| |
| Text Munging |
| ^^^^^^^^^^^^ |
| |
| :func:`sub` replaces every occurrence of a pattern with a string or the |
| result of a function. This example demonstrates using :func:`sub` with |
| a function to "munge" text, or randomize the order of all the characters |
| in each word of a sentence except for the first and last characters:: |
| |
| >>> def repl(m): |
| ... inner_word = list(m.group(2)) |
| ... random.shuffle(inner_word) |
| ... return m.group(1) + "".join(inner_word) + m.group(3) |
| >>> text = "Professor Abdolmalek, please report your absences promptly." |
| >>> re.sub(r"(\w)(\w+)(\w)", repl, text) |
| 'Poefsrosr Aealmlobdk, pslaee reorpt your abnseces plmrptoy.' |
| >>> re.sub(r"(\w)(\w+)(\w)", repl, text) |
| 'Pofsroser Aodlambelk, plasee reoprt yuor asnebces potlmrpy.' |
| |
| |
| Finding all Adverbs |
| ^^^^^^^^^^^^^^^^^^^ |
| |
| :func:`findall` matches *all* occurrences of a pattern, not just the first |
| one as :func:`search` does. For example, if one was a writer and wanted to |
| find all of the adverbs in some text, he or she might use :func:`findall` in |
| the following manner: |
| |
| >>> text = "He was carefully disguised but captured quickly by police." |
| >>> re.findall(r"\w+ly", text) |
| ['carefully', 'quickly'] |
| |
| |
| Finding all Adverbs and their Positions |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| If one wants more information about all matches of a pattern than the matched |
| text, :func:`finditer` is useful as it provides :ref:`match objects |
| <match-objects>` instead of strings. Continuing with the previous example, if |
| one was a writer who wanted to find all of the adverbs *and their positions* in |
| some text, he or she would use :func:`finditer` in the following manner: |
| |
| >>> text = "He was carefully disguised but captured quickly by police." |
| >>> for m in re.finditer(r"\w+ly", text): |
| ... print('%02d-%02d: %s' % (m.start(), m.end(), m.group(0))) |
| 07-16: carefully |
| 40-47: quickly |
| |
| |
| Raw String Notation |
| ^^^^^^^^^^^^^^^^^^^ |
| |
| Raw string notation (``r"text"``) keeps regular expressions sane. Without it, |
| every backslash (``'\'``) in a regular expression would have to be prefixed with |
| another one to escape it. For example, the two following lines of code are |
| functionally identical: |
| |
| >>> re.match(r"\W(.)\1\W", " ff ") |
| <_sre.SRE_Match object at ...> |
| >>> re.match("\\W(.)\\1\\W", " ff ") |
| <_sre.SRE_Match object at ...> |
| |
| When one wants to match a literal backslash, it must be escaped in the regular |
| expression. With raw string notation, this means ``r"\\"``. Without raw string |
| notation, one must use ``"\\\\"``, making the following lines of code |
| functionally identical: |
| |
| >>> re.match(r"\\", r"\\") |
| <_sre.SRE_Match object at ...> |
| >>> re.match("\\\\", r"\\") |
| <_sre.SRE_Match object at ...> |