Added\p{Horiz_Space} and\p{Vert_Space} (GitHub issue 477)

\p{Horiz_Space} or\p{H} matches horizontal whitespace and\p{Vert_Space} or\p{V} matches vertical whitespace.

Added support for lookaround in conditional pattern (Hg issue 163)

The test of a conditional pattern can be a lookaround.

>>>regex.match(r'(?(?=\d)\d+|\w+)','123abc')<regex.Matchobject;span=(0,3),match='123'>>>>regex.match(r'(?(?=\d)\d+|\w+)','abc123')<regex.Matchobject;span=(0,6),match='abc123'>

This is not quite the same as putting a lookaround in the first branch of a pair of alternatives.

>>>print(regex.match(r'(?:(?=\d)\d+\b|\w+)','123abc'))<regex.Matchobject;span=(0,6),match='123abc'>>>>print(regex.match(r'(?(?=\d)\d+\b|\w+)','123abc'))None

In the first example, the lookaround matched, but the remainder of the first branch failed to match, and so the second branch was attempted, whereas in the second example, the lookaround matched, and the first branch failed to match, but the second branch wasnot attempted.

Added POSIX matching (leftmost longest) (Hg issue 150)

The POSIX standard for regex is to return the leftmost longest match. This can be turned on using thePOSIX flag.

>>># Normal matching.>>>regex.search(r'Mr|Mrs','Mrs')<regex.Matchobject;span=(0,2),match='Mr'>>>>regex.search(r'one(self)?(selfsufficient)?','oneselfsufficient')<regex.Matchobject;span=(0,7),match='oneself'>>>># POSIX matching.>>>regex.search(r'(?p)Mr|Mrs','Mrs')<regex.Matchobject;span=(0,3),match='Mrs'>>>>regex.search(r'(?p)one(self)?(selfsufficient)?','oneselfsufficient')<regex.Matchobject;span=(0,17),match='oneselfsufficient'>

Note that it will take longer to find matches because when it finds a match at a certain position, it won’t return that immediately, but will keep looking to see if there’s another longer match there.

Added(?(DEFINE)...) (Hg issue 152)

If there’s no group called “DEFINE”, then … will be ignored except that any groups defined within it can be called and that the normal rules for numbering groups still apply.

>>>regex.search(r'(?(DEFINE)(?P<quant>\d+)(?P<item>\w+))(?&quant) (?&item)','5 elephants')<regex.Matchobject;span=(0,11),match='5 elephants'>

Added(*PRUNE),(*SKIP) and(*FAIL) (Hg issue 153)

(*PRUNE) discards the backtracking info up to that point. When used in an atomic group or a lookaround, it won’t affect the enclosing pattern.

(*SKIP) is similar to(*PRUNE), except that it also sets where in the text the next attempt to match will start. When used in an atomic group or a lookaround, it won’t affect the enclosing pattern.

(*FAIL) causes immediate backtracking.(*F) is a permitted abbreviation.

Added\K (Hg issue 151)

Keeps the part of the entire match after the position where\K occurred; the part before it is discarded.

It does not affect what groups return.

>>>m=regex.search(r'(\w\w\K\w\w\w)','abcdef')>>>m[0]'cde'>>>m[1]'abcde'>>>>>>m=regex.search(r'(?r)(\w\w\K\w\w\w)','abcdef')>>>m[0]'bc'>>>m[1]'bcdef'

Added capture subscripting forexpandf andsubf/subfn (Hg issue 133)

You can use subscripting to get the captures of a repeated group.

>>>m=regex.match(r"(\w)+","abc")>>>m.expandf("{1}")'c'>>>m.expandf("{1[0]}{1[1]}{1[2]}")'a b c'>>>m.expandf("{1[-1]}{1[-2]}{1[-3]}")'c b a'>>>>>>m=regex.match(r"(?P<letter>\w)+","abc")>>>m.expandf("{letter}")'c'>>>m.expandf("{letter[0]}{letter[1]}{letter[2]}")'a b c'>>>m.expandf("{letter[-1]}{letter[-2]}{letter[-3]}")'c b a'

Added support for referring to a group by number using(?P=...)

This is in addition to the existing\g<...>.

Fixed the handling of locale-sensitive regexes

TheLOCALE flag is intended for legacy code and has limited support. You’re still recommended to use Unicode instead.

Added partial matches (Hg issue 102)

A partial match is one that matches up to the end of string, but that string has been truncated and you want to know whether a complete match could be possible if the string had not been truncated.

Partial matches are supported bymatch,search,fullmatch andfinditer with thepartial keyword argument.

Match objects have apartial attribute, which isTrue if it’s a partial match.

For example, if you wanted a user to enter a 4-digit number and check it character by character as it was being entered:

>>>pattern=regex.compile(r'\d{4}')>>># Initially, nothing has been entered:>>>print(pattern.fullmatch('',partial=True))<regex.Matchobject;span=(0,0),match='',partial=True>>>># An empty string is OK, but it's only a partial match.>>># The user enters a letter:>>>print(pattern.fullmatch('a',partial=True))None>>># It'll never match.>>># The user deletes that and enters a digit:>>>print(pattern.fullmatch('1',partial=True))<regex.Matchobject;span=(0,1),match='1',partial=True>>>># It matches this far, but it's only a partial match.>>># The user enters 2 more digits:>>>print(pattern.fullmatch('123',partial=True))<regex.Matchobject;span=(0,3),match='123',partial=True>>>># It matches this far, but it's only a partial match.>>># The user enters another digit:>>>print(pattern.fullmatch('1234',partial=True))<regex.Matchobject;span=(0,4),match='1234'>>>># It's a complete match.>>># If the user enters another digit:>>>print(pattern.fullmatch('12345',partial=True))None>>># It's no longer a match.>>># This is a partial match:>>>pattern.match('123',partial=True).partialTrue>>># This is a complete match:>>>pattern.match('1233',partial=True).partialFalse

* operator not working correctly with sub() (Hg issue 106)

Sometimes it’s not clear how zero-width matches should be handled. For example, should.* match 0 characters directly after matching >0 characters?

>>>regex.sub('.*','x','test')'xx'>>>regex.sub('.*?','|','test')'|||||||||'

Addedcapturesdict (Hg issue 86)

capturesdict is a combination ofgroupdict andcaptures:

groupdict returns a dict of the named groups and the last capture of those groups.

captures returns a list of all the captures of a group

capturesdict returns a dict of the named groups and lists of all the captures of those groups.

>>>m=regex.match(r"(?:(?P<word>\w+) (?P<digits>\d+)\n)+","one 1\ntwo 2\nthree 3\n")>>>m.groupdict(){'word':'three','digits':'3'}>>>m.captures("word")['one','two','three']>>>m.captures("digits")['1','2','3']>>>m.capturesdict(){'word':['one','two','three'],'digits':['1','2','3']}

Addedallcaptures andallspans (Git issue 474)

allcaptures returns a list of all the captures of all the groups.

allspans returns a list of all the spans of the all captures of all the groups.

>>>m=regex.match(r"(?:(?P<word>\w+) (?P<digits>\d+)\n)+","one 1\ntwo 2\nthree 3\n")>>>m.allcaptures()(['one 1\ntwo 2\nthree 3\n'],['one','two','three'],['1','2','3'])>>>m.allspans()([(0,20)],[(0,3),(6,9),(12,17)],[(4,5),(10,11),(18,19)])

Allow duplicate names of groups (Hg issue 87)

Group names can be duplicated.

>>># With optional groups:>>>>>># Both groups capture, the second capture 'overwriting' the first.>>>m=regex.match(r"(?P<item>\w+)? or (?P<item>\w+)?","first or second")>>>m.group("item")'second'>>>m.captures("item")['first','second']>>># Only the second group captures.>>>m=regex.match(r"(?P<item>\w+)? or (?P<item>\w+)?"," or second")>>>m.group("item")'second'>>>m.captures("item")['second']>>># Only the first group captures.>>>m=regex.match(r"(?P<item>\w+)? or (?P<item>\w+)?","first or ")>>>m.group("item")'first'>>>m.captures("item")['first']>>>>>># With mandatory groups:>>>>>># Both groups capture, the second capture 'overwriting' the first.>>>m=regex.match(r"(?P<item>\w*) or (?P<item>\w*)?","first or second")>>>m.group("item")'second'>>>m.captures("item")['first','second']>>># Again, both groups capture, the second capture 'overwriting' the first.>>>m=regex.match(r"(?P<item>\w*) or (?P<item>\w*)"," or second")>>>m.group("item")'second'>>>m.captures("item")['','second']>>># And yet again, both groups capture, the second capture 'overwriting' the first.>>>m=regex.match(r"(?P<item>\w*) or (?P<item>\w*)","first or ")>>>m.group("item")''>>>m.captures("item")['first','']

Addedfullmatch (issue #16203)

fullmatch behaves likematch, except that it must match all of the string.

>>>print(regex.fullmatch(r"abc","abc").span())(0,3)>>>print(regex.fullmatch(r"abc","abcx"))None>>>print(regex.fullmatch(r"abc","abcx",endpos=3).span())(0,3)>>>print(regex.fullmatch(r"abc","xabcy",pos=1,endpos=4).span())(1,4)>>>>>>regex.match(r"a.*?","abcd").group(0)'a'>>>regex.fullmatch(r"a.*?","abcd").group(0)'abcd'

Addedsubf andsubfn

subf andsubfn are alternatives tosub andsubn respectively. When passed a replacement string, they treat it as a format string.

>>>regex.subf(r"(\w+) (\w+)","{0} =>{2}{1}","foo bar")'foo bar => bar foo'>>>regex.subf(r"(?P<word1>\w+) (?P<word2>\w+)","{word2}{word1}","foo bar")'bar foo'

Addedexpandf to match object

expandf is an alternative toexpand. When passed a replacement string, it treats it as a format string.

>>>m=regex.match(r"(\w+) (\w+)","foo bar")>>>m.expandf("{0} =>{2}{1}")'foo bar => bar foo'>>>>>>m=regex.match(r"(?P<word1>\w+) (?P<word2>\w+)","foo bar")>>>m.expandf("{word2}{word1}")'bar foo'

Detach searched string

A match object contains a reference to the string that was searched, via itsstring attribute. Thedetach_string method will ‘detach’ that string, making it available for garbage collection, which might save valuable memory if that string is very large.

>>>m=regex.search(r"\w+","Hello world")>>>print(m.group())Hello>>>print(m.string)Helloworld>>>m.detach_string()>>>print(m.group())Hello>>>print(m.string)None

Recursive patterns (Hg issue 27)

Recursive and repeated patterns are supported.

(?R) or(?0) tries to match the entire regex recursively.(?1),(?2), etc, try to match the relevant group.

(?&name) tries to match the named group.

>>>regex.match(r"(Tarzan|Jane) loves (?1)","Tarzan loves Jane").groups()('Tarzan',)>>>regex.match(r"(Tarzan|Jane) loves (?1)","Jane loves Tarzan").groups()('Jane',)>>>m=regex.search(r"(\w)(?:(?R)|(\w?))\1","kayak")>>>m.group(0,1,2)('kayak','k',None)

The first two examples show how the subpattern within the group is reused, but is _not_ itself a group. In other words,"(Tarzan|Jane) loves(?1)" is equivalent to"(Tarzan|Jane) loves(?:Tarzan|Jane)".

It’s possible to backtrack into a recursed or repeated group.

You can’t call a group if there is more than one group with that group name or group number ("ambiguous group reference").

The alternative forms(?P>name) and(?P&name) are also supported.

Full Unicode case-folding is supported

In version 1 behaviour, the regex module uses full case-folding when performing case-insensitive matches in Unicode.

>>>regex.match(r"(?iV1)strasse","stra\N{LATIN SMALL LETTER SHARP S}e").span()(0,6)>>>regex.match(r"(?iV1)stra\N{LATIN SMALL LETTER SHARP S}e","STRASSE").span()(0,7)

In version 0 behaviour, it uses simple case-folding for backward compatibility with the re module.

Approximate “fuzzy” matching (Hg issue 12,Hg issue 41,Hg issue 109)

Regex usually attempts an exact match, but sometimes an approximate, or “fuzzy”, match is needed, for those cases where the text being searched may contain errors in the form of inserted, deleted or substituted characters.

A fuzzy regex specifies which types of errors are permitted, and, optionally, either the minimum and maximum or only the maximum permitted number of each type. (You cannot specify only a minimum.)

The 3 types of error are:

• Insertion, indicated by “i”

• Deletion, indicated by “d”

• Substitution, indicated by “s”

In addition, “e” indicates any type of error.

The fuzziness of a regex item is specified between “{” and “}” after the item.

Examples:

• foo match “foo” exactly

• (?:foo){i} match “foo”, permitting insertions

• (?:foo){d} match “foo”, permitting deletions

• (?:foo){s} match “foo”, permitting substitutions

• (?:foo){i,s} match “foo”, permitting insertions and substitutions

• (?:foo){e} match “foo”, permitting errors

If a certain type of error is specified, then any type not specified willnot be permitted.

In the following examples I’ll omit the item and write only the fuzziness:

• {d<=3} permit at most 3 deletions, but no other types

• {i<=1,s<=2} permit at most 1 insertion and at most 2 substitutions, but no deletions

• {1<=e<=3} permit at least 1 and at most 3 errors

• {i<=2,d<=2,e<=3} permit at most 2 insertions, at most 2 deletions, at most 3 errors in total, but no substitutions

It’s also possible to state the costs of each type of error and the maximum permitted total cost.

Examples:

• {2i+2d+1s<=4} each insertion costs 2, each deletion costs 2, each substitution costs 1, the total cost must not exceed 4

• {i<=1,d<=1,s<=1,2i+2d+1s<=4} at most 1 insertion, at most 1 deletion, at most 1 substitution; each insertion costs 2, each deletion costs 2, each substitution costs 1, the total cost must not exceed 4

You can also use “<” instead of “<=” if you want an exclusive minimum or maximum.

You can add a test to perform on a character that’s substituted or inserted.

Examples:

• {s<=2:[a-z]} at most 2 substitutions, which must be in the character set[a-z].

• {s<=2,i<=3:\d} at most 2 substitutions, at most 3 insertions, which must be digits.

By default, fuzzy matching searches for the first match that meets the given constraints. TheENHANCEMATCH flag will cause it to attempt to improve the fit (i.e. reduce the number of errors) of the match that it has found.

TheBESTMATCH flag will make it search for the best match instead.

Further examples to note:

• regex.search("(dog){e}", "cat anddog")[1] returns"cat" because that matches"dog" with 3 errors (an unlimited number of errors is permitted).

• regex.search("(dog){e<=1}", "cat anddog")[1] returns" dog" (with a leading space) because that matches"dog" with 1 error, which is within the limit.

• regex.search("(?e)(dog){e<=1}", "cat anddog")[1] returns"dog" (without a leading space) because the fuzzy search matches" dog" with 1 error, which is within the limit, and the(?e) then it attempts a better fit.

In the first two examples there are perfect matches later in the string, but in neither case is it the first possible match.

The match object has an attributefuzzy_counts which gives the total number of substitutions, insertions and deletions.

>>># A 'raw' fuzzy match:>>>regex.fullmatch(r"(?:cats|cat){e<=1}","cat").fuzzy_counts(0,0,1)>>># 0 substitutions, 0 insertions, 1 deletion.>>># A better match might be possible if the ENHANCEMATCH flag used:>>>regex.fullmatch(r"(?e)(?:cats|cat){e<=1}","cat").fuzzy_counts(0,0,0)>>># 0 substitutions, 0 insertions, 0 deletions.

The match object also has an attributefuzzy_changes which gives a tuple of the positions of the substitutions, insertions and deletions.

>>>m=regex.search('(fuu){i<=2,d<=2,e<=5}','anaconda foo bar')>>>m<regex.Matchobject;span=(7,10),match='a f',fuzzy_counts=(0,2,2)>>>>m.fuzzy_changes([],[7,8],[10,11])

What this means is that if the matched part of the string had been:

'anacondfuuoo bar'

it would’ve been an exact match.

However, there were insertions at positions 7 and 8:

'anaconda fuuoo bar'^^

and deletions at positions 10 and 11:

'anaconda f~~oo bar'^^

So the actual string was:

'anaconda foo bar'

Named lists\L<name> (Hg issue 11)

There are occasions where you may want to include a list (actually, a set) of options in a regex.

One way is to build the pattern like this:

>>>p=regex.compile(r"first|second|third|fourth|fifth")

but if the list is large, parsing the resulting regex can take considerable time, and care must also be taken that the strings are properly escaped and properly ordered, for example, “cats” before “cat”.

The new alternative is to use a named list:

>>>option_set=["first","second","third","fourth","fifth"]>>>p=regex.compile(r"\L<options>",options=option_set)

The order of the items is irrelevant, they are treated as a set. The named lists are available as the.named_lists attribute of the pattern object :

>>>print(p.named_lists){'options':frozenset({'third','first','fifth','fourth','second'})}

If there are any unused keyword arguments,ValueError will be raised unless you tell it otherwise:

>>>option_set=["first","second","third","fourth","fifth"]>>>p=regex.compile(r"\L<options>",options=option_set,other_options=[])Traceback(mostrecentcalllast):File"<stdin>",line1,in<module>File"C:\Python310\lib\site-packages\regex\regex.py",line353,incompilereturn_compile(pattern,flags,ignore_unused,kwargs,cache_pattern)File"C:\Python310\lib\site-packages\regex\regex.py",line500,in_compilecomplain_unused_args()File"C:\Python310\lib\site-packages\regex\regex.py",line483,incomplain_unused_argsraiseValueError('unused keyword argument{!a}'.format(any_one))ValueError:unusedkeywordargument'other_options'>>>p=regex.compile(r"\L<options>",options=option_set,other_options=[],ignore_unused=True)>>>p=regex.compile(r"\L<options>",options=option_set,other_options=[],ignore_unused=False)Traceback(mostrecentcalllast):File"<stdin>",line1,in<module>File"C:\Python310\lib\site-packages\regex\regex.py",line353,incompilereturn_compile(pattern,flags,ignore_unused,kwargs,cache_pattern)File"C:\Python310\lib\site-packages\regex\regex.py",line500,in_compilecomplain_unused_args()File"C:\Python310\lib\site-packages\regex\regex.py",line483,incomplain_unused_argsraiseValueError('unused keyword argument{!a}'.format(any_one))ValueError:unusedkeywordargument'other_options'>>>

Start and end of word

\m matches at the start of a word.

\M matches at the end of a word.

Compare with\b, which matches at the start or end of a word.

Unicode line separators

Normally the only line separator is\n (\x0A), but if theWORD flag is turned on then the line separators are\x0D\x0A,\x0A,\x0B,\x0C and\x0D, plus\x85,\u2028 and\u2029 when working with Unicode.

This affects the regex dot".", which, with theDOTALL flag turned off, matches any character except a line separator. It also affects the line anchors^ and$ (in multiline mode).

Set operators

Version 1 behaviour only

Set operators have been added, and a set[...] can include nested sets.

The operators, in order of increasing precedence, are:

• || for union (“x||y” means “x or y”)

• ~~ (double tilde) for symmetric difference (“x~~y” means “x or y, but not both”)

• && for intersection (“x&&y” means “x and y”)

• -- (double dash) for difference (“x–y” means “x but not y”)

Implicit union, ie, simple juxtaposition like in[ab], has the highest precedence. Thus,[ab&&cd] is the same as[[a||b]&&[c||d]].

Examples:

• [ab] # Set containing ‘a’ and ‘b’

• [a-z] # Set containing ‘a’ .. ‘z’

• [[a-z]--[qw]] # Set containing ‘a’ .. ‘z’, but not ‘q’ or ‘w’

• [a-z--qw] # Same as above

• [\p{L}--QW] # Set containing all letters except ‘Q’ and ‘W’

• [\p{N}--[0-9]] # Set containing all numbers except ‘0’ .. ‘9’

• [\p{ASCII}&&\p{Letter}] # Set containing all characters which are ASCII and letter

regex.escape (issue #2650)

regex.escape has an additional keyword parameterspecial_only. When True, only ‘special’ regex characters, such as ‘?’, are escaped.

>>>regex.escape("foo!?",special_only=False)'foo\\!\\?'>>>regex.escape("foo!?",special_only=True)'foo!\\?'

regex.escape (Hg issue 249)

regex.escape has an additional keyword parameterliteral_spaces. When True, spaces are not escaped.

>>>regex.escape("foo bar!?",literal_spaces=False)'foo\\ bar!\\?'>>>regex.escape("foo bar!?",literal_spaces=True)'foo bar!\\?'

Repeated captures (issue #7132)

A match object has additional methods which return information on all the successful matches of a repeated group. These methods are:

• matchobject.captures([group1,...])

  • Returns a list of the strings matched in a group or groups. Compare withmatchobject.group([group1,...]).

• matchobject.starts([group])

  • Returns a list of the start positions. Compare withmatchobject.start([group]).

• matchobject.ends([group])

  • Returns a list of the end positions. Compare withmatchobject.end([group]).

• matchobject.spans([group])

  • Returns a list of the spans. Compare withmatchobject.span([group]).

>>>m=regex.search(r"(\w{3})+","123456789")>>>m.group(1)'789'>>>m.captures(1)['123','456','789']>>>m.start(1)6>>>m.starts(1)[0,3,6]>>>m.end(1)9>>>m.ends(1)[3,6,9]>>>m.span(1)(6,9)>>>m.spans(1)[(0,3),(3,6),(6,9)]

Atomic grouping(?>...) (issue #433030)

If the following pattern subsequently fails, then the subpattern as a whole will fail.

Possessive quantifiers

(?:...)?+ ;(?:...)*+ ;(?:...)++ ;(?:...){min,max}+

The subpattern is matched up to ‘max’ times. If the following pattern subsequently fails, then all the repeated subpatterns will fail as a whole. For example,(?:...)++ is equivalent to(?>(?:...)+).

Scoped flags (issue #433028)

(?flags-flags:...)

The flags will apply only to the subpattern. Flags can be turned on or off.

Definition of ‘word’ character (issue #1693050)

The definition of a ‘word’ character has been expanded for Unicode. It conforms to the Unicode specification athttp://www.unicode.org/reports/tr29/.

Variable-length lookbehind

A lookbehind can match a variable-length string.

Flags argument for regex.split, regex.sub and regex.subn (issue #3482)

regex.split,regex.sub andregex.subn support a ‘flags’ argument.

Pos and endpos arguments for regex.sub and regex.subn

regex.sub andregex.subn support ‘pos’ and ‘endpos’ arguments.

‘Overlapped’ argument for regex.findall and regex.finditer

regex.findall andregex.finditer support an ‘overlapped’ flag which permits overlapped matches.

Splititer

regex.splititer has been added. It’s a generator equivalent ofregex.split.

Subscripting match objects for groups

A match object accepts access to the groups via subscripting and slicing:

>>>m=regex.search(r"(?P<before>.*?)(?P<num>\d+)(?P<after>.*)","pqr123stu")>>>print(m["before"])pqr>>>print(len(m))4>>>print(m[:])('pqr123stu','pqr','123','stu')

Named groups

Groups can be named with(?<name>...) as well as the existing(?P<name>...).

Group references

Groups can be referenced within a pattern with\g<name>. This also allows there to be more than 99 groups.

Named characters\N{name}

Named characters are supported. Note that only those known by Python’s Unicode database will be recognised.

Unicode codepoint properties, including scripts and blocks

\p{property=value};\P{property=value};\p{value} ;\P{value}

Many Unicode properties are supported, including blocks and scripts.\p{property=value} or\p{property:value} matches a character whose propertyproperty has valuevalue. The inverse of\p{property=value} is\P{property=value} or\p{^property=value}.

If the short form\p{value} is used, the properties are checked in the order:General_Category,Script,Block, binary property:

• Latin, the ‘Latin’ script (Script=Latin).

• BasicLatin, the ‘BasicLatin’ block (Block=BasicLatin).

• Alphabetic, the ‘Alphabetic’ binary property (Alphabetic=Yes).

A short form starting withIs indicates a script or binary property:

• IsLatin, the ‘Latin’ script (Script=Latin).

• IsAlphabetic, the ‘Alphabetic’ binary property (Alphabetic=Yes).

A short form starting withIn indicates a block property:

• InBasicLatin, the ‘BasicLatin’ block (Block=BasicLatin).

POSIX character classes

[[:alpha:]];[[:^alpha:]]

POSIX character classes are supported. These are normally treated as an alternative form of\p{...}.

The exceptions arealnum,digit,punct andxdigit, whose definitions are different from those of Unicode.

[[:alnum:]] is equivalent to\p{posix_alnum}.

[[:digit:]] is equivalent to\p{posix_digit}.

[[:punct:]] is equivalent to\p{posix_punct}.

[[:xdigit:]] is equivalent to\p{posix_xdigit}.

Search anchor\G

A search anchor has been added. It matches at the position where each search started/continued and can be used for contiguous matches or in negative variable-length lookbehinds to limit how far back the lookbehind goes:

>>>regex.findall(r"\w{2}","abcd ef")['ab','cd','ef']>>>regex.findall(r"\G\w{2}","abcd ef")['ab','cd']

• The search starts at position 0 and matches ‘ab’.

• The search continues at position 2 and matches ‘cd’.

• The search continues at position 4 and fails to match any letters.

• The anchor stops the search start position from being advanced, so there are no more results.

Reverse searching

Searches can also work backwards:

>>>regex.findall(r".","abc")['a','b','c']>>>regex.findall(r"(?r).","abc")['c','b','a']

Note that the result of a reverse search is not necessarily the reverse of a forward search:

>>>regex.findall(r"..","abcde")['ab','cd']>>>regex.findall(r"(?r)..","abcde")['de','bc']

Matching a single grapheme\X

The grapheme matcher is supported. It conforms to the Unicode specification athttp://www.unicode.org/reports/tr29/.

Branch reset(?|...|...)

Group numbers will be reused across the alternatives, but groups with different names will have different group numbers.

>>>regex.match(r"(?|(first)|(second))","first").groups()('first',)>>>regex.match(r"(?|(first)|(second))","second").groups()('second',)

Note that there is only one group.

Default Unicode word boundary

TheWORD flag changes the definition of a ‘word boundary’ to that of a default Unicode word boundary. This applies to\b and\B.

Timeout

The matching methods and functions support timeouts. The timeout (in seconds) applies to the entire operation:

>>>fromtimeimportsleep>>>>>>deffast_replace(m):...return'X'...>>>defslow_replace(m):...sleep(0.5)...return'X'...>>>regex.sub(r'[a-z]',fast_replace,'abcde',timeout=2)'XXXXX'>>>regex.sub(r'[a-z]',slow_replace,'abcde',timeout=2)Traceback(mostrecentcalllast):File"<stdin>",line1,in<module>File"C:\Python310\lib\site-packages\regex\regex.py",line278,insubreturnpat.sub(repl,string,count,pos,endpos,concurrent,timeout)TimeoutError:regextimedout