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Many markup changes (to \regexp, mostly) 

Clarified text on 8-bit cleanness, complemented sets like [^5], and {m,n}
  qualifier.
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Andrew M. Kuchling 1998-04-09 14:56:04 +00:00
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Doc/lib/libre.tex
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@ -4,25 +4,28 @@
\bimodindex{re} \bimodindex{re}
This module provides regular expression matching operations similar to This module provides regular expression matching operations similar to
those found in Perl. It's 8-bit clean: both patterns and strings may those found in Perl. It's 8-bit clean: the strings being processed
contain null bytes and characters whose high bit is set. It is always may contain both null bytes and characters whose high bit is set. Regular
expression patterns may not contain null bytes, but they may contain
characters with the high bit set. The \module{re} module is always
available. available.
Regular expressions use the backslash character (\samp{\e}) to Regular expressions use the backslash character (\character{\e}) to
indicate special forms or to allow special characters to be used indicate special forms or to allow special characters to be used
without invoking their special meaning. This collides with Python's without invoking their special meaning. This collides with Python's
usage of the same character for the same purpose in string literals; usage of the same character for the same purpose in string literals;
for example, to match a literal backslash, one might have to write for example, to match a literal backslash, one might have to write
\samp{\e\e\e\e} as the pattern string, because the regular expression \code{'\e\e\e\e'} as the pattern string, because the regular expression
must be \samp{\e\e}, and each backslash must be expressed as must be \samp{\e\e}, and each backslash must be expressed as
\samp{\e\e} inside a regular Python string literal. \samp{\e\e} inside a regular Python string literal.
The solution is to use Python's raw string notation for regular The solution is to use Python's raw string notation for regular
expression patterns; backslashes are not handled in any special way in expression patterns; backslashes are not handled in any special way in
a string literal prefixed with 'r'. So \code{r"\e n"} is a two a string literal prefixed with \character{r}. So \code{r"\e n"} is a
character string containing a backslash and the letter 'n', while two-character string containing \character{\e} and \character{n},
\code{"\e n"} is a one-character string containing a newline. Usually while \code{"\e n"} is a one-character string containing a newline.
patterns will be expressed in Python code using this raw string notation. Usually patterns will be expressed in Python code using this raw
string notation.
\subsection{Regular Expression Syntax} \subsection{Regular Expression Syntax}
@ -45,14 +48,14 @@ A brief explanation of the format of regular expressions follows.
%For further information and a gentler presentation, consult XXX somewhere. %For further information and a gentler presentation, consult XXX somewhere.
Regular expressions can contain both special and ordinary characters. Regular expressions can contain both special and ordinary characters.
Most ordinary characters, like \samp{A}, \samp{a}, or \samp{0}, Most ordinary characters, like \character{A}, \character{a}, or \character{0},
are the simplest regular expressions; they simply match themselves. are the simplest regular expressions; they simply match themselves.
You can concatenate ordinary characters, so \samp{last} matches the You can concatenate ordinary characters, so \regexp{last} matches the
characters 'last'. (In the rest of this section, we'll write RE's in string \code{'last'}. (In the rest of this section, we'll write RE's in
\code{this special font}, usually without quotes, and strings to be \regexp{this special style}, usually without quotes, and strings to be
matched 'in single quotes'.) matched \code{'in single quotes'}.)
Some characters, like \samp{|} or \samp{(}, are special. Special Some characters, like \character{|} or \character{(}, are special. Special
characters either stand for classes of ordinary characters, or affect characters either stand for classes of ordinary characters, or affect
how the regular expressions around them are interpreted. how the regular expressions around them are interpreted.
@ -61,56 +64,58 @@ The special characters are:
\newcommand{\MyLeftMargin}{0.7in} \newcommand{\MyLeftMargin}{0.7in}
\newcommand{\MyLabelWidth}{0.65in} \newcommand{\MyLabelWidth}{0.65in}
\begin{list}{}{\leftmargin \MyLeftMargin \labelwidth \MyLabelWidth} \begin{list}{}{\leftmargin \MyLeftMargin \labelwidth \MyLabelWidth}
\item[\code{.}] (Dot.) In the default mode, this matches any \item[\character{.}] (Dot.) In the default mode, this matches any
character except a newline. If the \constant{DOTALL} flag has been character except a newline. If the \constant{DOTALL} flag has been
specified, this matches any character including a newline. specified, this matches any character including a newline.
% %
\item[\code{\^}] (Caret.) Matches the start of the string, and in \item[\character{\^}] (Caret.) Matches the start of the string, and in
\constant{MULTILINE} mode also immediately after each newline. \constant{MULTILINE} mode also matches immediately after each newline.
% %
\item[\code{\$}] Matches the end of the string, and in \item[\character{\$}] Matches the end of the string, and in
\constant{MULTILINE} mode also matches before a newline. \constant{MULTILINE} mode also matches before a newline.
\code{foo} matches both 'foo' and 'foobar', while the regular \regexp{foo} matches both 'foo' and 'foobar', while the regular
expression \code{foo\$} matches only 'foo'. expression \regexp{foo\$} matches only 'foo'.
% %
\item[\code{*}] Causes the resulting RE to \item[\character{*}] Causes the resulting RE to
match 0 or more repetitions of the preceding RE, as many repetitions match 0 or more repetitions of the preceding RE, as many repetitions
as are possible. \code{ab*} will as are possible. \regexp{ab*} will
match 'a', 'ab', or 'a' followed by any number of 'b's. match 'a', 'ab', or 'a' followed by any number of 'b's.
% %
\item[\code{+}] Causes the \item[\character{+}] Causes the
resulting RE to match 1 or more repetitions of the preceding RE. resulting RE to match 1 or more repetitions of the preceding RE.
\code{ab+} will match 'a' followed by any non-zero number of 'b's; it \regexp{ab+} will match 'a' followed by any non-zero number of 'b's; it
will not match just 'a'. will not match just 'a'.
% %
\item[\code{?}] Causes the resulting RE to \item[\character{?}] Causes the resulting RE to
match 0 or 1 repetitions of the preceding RE. \code{ab?} will match 0 or 1 repetitions of the preceding RE. \regexp{ab?} will
match either 'a' or 'ab'. match either 'a' or 'ab'.
\item[\code{*?}, \code{+?}, \code{??}] The \code{*}, \code{+}, and \item[\code{*?}, \code{+?}, \code{??}] The \character{*}, \character{+}, and
\code{?} qualifiers are all \dfn{greedy}; they match as much text as \character{?} qualifiers are all \dfn{greedy}; they match as much text as
possible. Sometimes this behaviour isn't desired; if the RE possible. Sometimes this behaviour isn't desired; if the RE
\code{<.*>} is matched against \code{<H1>title</H1>}, it will match the \regexp{<.*>} is matched against \code{'<H1>title</H1>'}, it will match the
entire string, and not just \code{<H1>}. entire string, and not just \code{'<H1>'}.
Adding \code{?} after the qualifier makes it perform the match in Adding \character{?} after the qualifier makes it perform the match in
\dfn{non-greedy} or \dfn{minimal} fashion; as few characters as \dfn{non-greedy} or \dfn{minimal} fashion; as \emph{few} characters as
possible will be matched. Using \code{.*?} in the previous possible will be matched. Using \regexp{.*?} in the previous
expression will match only \code{<H1>}. expression will match only \code{'<H1>'}.
% %
\item[\code{\{\var{m},\var{n}\}}] Causes the resulting RE to match from \item[\code{\{\var{m},\var{n}\}}] Causes the resulting RE to match from
\var{m} to \var{n} repetitions of the preceding RE, attempting to \var{m} to \var{n} repetitions of the preceding RE, attempting to
match as many repetitions as possible. For example, \code{a\{3,5\}} match as many repetitions as possible. For example, \regexp{a\{3,5\}}
will match from 3 to 5 'a' characters. will match from 3 to 5 \character{a} characters. Omitting \var{m} is the same
as specifying 0 for the lower bound; omitting \var{n} specifies an
infinite upper bound.
% %
\item[\code{\{\var{m},\var{n}\}?}] Causes the resulting RE to \item[\code{\{\var{m},\var{n}\}?}] Causes the resulting RE to
match from \var{m} to \var{n} repetitions of the preceding RE, match from \var{m} to \var{n} repetitions of the preceding RE,
attempting to match as \emph{few} repetitions as possible. This is attempting to match as \emph{few} repetitions as possible. This is
the non-greedy version of the previous qualifier. For example, on the the non-greedy version of the previous qualifier. For example, on the
6-character string 'aaaaaa', \code{a\{3,5\}} will match 5 'a' 6-character string \code{'aaaaaa'}, \regexp{a\{3,5\}} will match 5 \character{a}
characters, while \code{a\{3,5\}?} will only match 3 characters. characters, while \regexp{a\{3,5\}?} will only match 3 characters.
% %
\item[\code{\e}] Either escapes special characters (permitting you to match \item[\character{\e}] Either escapes special characters (permitting you to match
characters like '*?+\&\$'), or signals a special sequence; special characters like \character{*}, \character{?}, and so forth), or
sequences are discussed below. signals a special sequence; special sequences are discussed below.
If you're not using a raw string to If you're not using a raw string to
express the pattern, remember that Python also uses the express the pattern, remember that Python also uses the
@ -124,42 +129,47 @@ simplest expressions.
% %
\item[\code{[]}] Used to indicate a set of characters. Characters can \item[\code{[]}] Used to indicate a set of characters. Characters can
be listed individually, or a range of characters can be indicated by be listed individually, or a range of characters can be indicated by
giving two characters and separating them by a '-'. Special giving two characters and separating them by a \character{-}. Special
characters are not active inside sets. For example, \code{[akm\$]} characters are not active inside sets. For example, \regexp{[akm\$]}
will match any of the characters \character{a}, \character{k}, will match any of the characters \character{a}, \character{k},
\character{m}, or \character{\$}; \code{[a-z]} \character{m}, or \character{\$}; \regexp{[a-z]}
will match any lowercase letter and \code{[a-zA-Z0-9]} matches any will match any lowercase letter, and \code{[a-zA-Z0-9]} matches any
letter or digit. Character classes such as \code{\e w} or \code {\e letter or digit. Character classes such as \code{\e w} or \code {\e
S} (defined below) are also acceptable inside a range. If you want to S} (defined below) are also acceptable inside a range. If you want to
include a \samp{]} or a \samp{-} inside a set, precede it with a include a \character{]} or a \character{-} inside a set, precede it with a
backslash. backslash, or place it as the first character. The
pattern \regexp{[]]} will match \code{']'}, for example.
You can match the characters not within a range by \dfn{complementing}
the set. This is indicated by including a
\character{\^} as the first character of the set; \character{\^} elsewhere will
simply match the \character{\^} character. For example, \regexp{[\^5]}
will match any character except \character{5}.
Characters \emph{not} within a range can be matched by including a
\code{\^} as the first character of the set; \code{\^} elsewhere will
simply match the \samp{\^} character.
% %
\item[\code{|}]\code{A|B}, where A and B can be arbitrary REs, \item[\character{|}]\code{A|B}, where A and B can be arbitrary REs,
creates a regular expression that will match either A or B. This can creates a regular expression that will match either A or B. This can
be used inside groups (see below) as well. To match a literal \samp{|}, be used inside groups (see below) as well. To match a literal \character{|},
use \code{\e|}, or enclose it inside a character class, like \code{[|]}. use \regexp{\e|}, or enclose it inside a character class, as in \regexp{[|]}.
% %
\item[\code{(...)}] Matches whatever regular expression is inside the \item[\code{(...)}] Matches whatever regular expression is inside the
parentheses, and indicates the start and end of a group; the contents 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 of a group can be retrieved after a match has been performed, and can
be matched later in the string with the \code{\e \var{number}} special be matched later in the string with the \regexp{\e \var{number}} special
sequence, described below. To match the literals '(' or ')', sequence, described below. To match the literals \character{(} or \character{')},
use \code{\e(} or \code{\e)}, or enclose them inside a character use \regexp{\e(} or \regexp{\e)}, or enclose them inside a character
class: \code{[(] [)]}. class: \regexp{[(] [)]}.
% %
\item[\code{(?...)}] This is an extension notation (a '?' following a \item[\code{(?...)}] This is an extension notation (a \character{?} following a
'(' is not meaningful otherwise). The first character after the '?' \character{(} is not meaningful otherwise). The first character after
the \character{?}
determines what the meaning and further syntax of the construct is. determines what the meaning and further syntax of the construct is.
Extensions usually do not create a new group; Extensions usually do not create a new group;
\code{(?P<\var{name}>...)} is the only exception to this rule. \regexp{(?P<\var{name}>...)} is the only exception to this rule.
Following are the currently supported extensions. Following are the currently supported extensions.
% %
\item[\code{(?iLmsx)}] (One or more letters from the set \samp{i}, \item[\code{(?iLmsx)}] (One or more letters from the set \character{i},
\samp{L}, \samp{m}, \samp{s}, \samp{x}.) The group matches \character{L}, \character{m}, \character{s}, \character{x}.) The group matches
the empty string; the letters set the corresponding flags the empty string; the letters set the corresponding flags
(\constant{re.I}, \constant{re.L}, \constant{re.M}, \constant{re.S}, (\constant{re.I}, \constant{re.L}, \constant{re.M}, \constant{re.S},
\constant{re.X}) for the entire regular expression. This is useful if \constant{re.X}) for the entire regular expression. This is useful if
@ -167,7 +177,8 @@ you wish to include the flags as part of the regular expression, instead
of passing a \var{flag} argument to the \function{compile()} function. of passing a \var{flag} argument to the \function{compile()} function.
% %
\item[\code{(?:...)}] A non-grouping version of regular parentheses. \item[\code{(?:...)}] A non-grouping version of regular parentheses.
Matches whatever's inside the parentheses, but the substring matched by the Matches whatever regular expression is inside the parentheses, but the
substring matched by the
group \emph{cannot} be retrieved after performing a match or group \emph{cannot} be retrieved after performing a match or
referenced later in the pattern. referenced later in the pattern.
% %
@ -179,10 +190,10 @@ named. So the group named 'id' in the example above can also be
referenced as the numbered group 1. referenced as the numbered group 1.
For example, if the pattern is For example, if the pattern is
\code{(?P<id>[a-zA-Z_]\e w*)}, the group can be referenced by its \regexp{(?P<id>[a-zA-Z_]\e w*)}, the group can be referenced by its
name in arguments to methods of match objects, such as \code{m.group('id')} name in arguments to methods of match objects, such as \code{m.group('id')}
or \code{m.end('id')}, and also by name in pattern text or \code{m.end('id')}, and also by name in pattern text
(e.g. \code{(?P=id)}) and replacement text (e.g. \code{\e g<id>}). (e.g. \regexp{(?P=id)}) and replacement text (e.g. \code{\e g<id>}).
% %
\item[\code{(?P=\var{name})}] Matches whatever text was matched by the \item[\code{(?P=\var{name})}] Matches whatever text was matched by the
earlier group named \var{name}. earlier group named \var{name}.
@ -190,34 +201,35 @@ earlier group named \var{name}.
\item[\code{(?\#...)}] A comment; the contents of the parentheses are \item[\code{(?\#...)}] A comment; the contents of the parentheses are
simply ignored. simply ignored.
% %
\item[\code{(?=...)}] Matches if \code{...} matches next, but doesn't \item[\code{(?=...)}] Matches if \regexp{...} matches next, but doesn't
consume any of the string. This is called a lookahead assertion. For consume any of the string. This is called a lookahead assertion. For
example, \code{Isaac (?=Asimov)} will match 'Isaac~' only if it's example, \regexp{Isaac (?=Asimov)} will match \code{'Isaac~'} only if it's
followed by 'Asimov'. followed by \code{'Asimov'}.
% %
\item[\code{(?!...)}] Matches if \code{...} doesn't match next. This \item[\code{(?!...)}] Matches if \regexp{...} doesn't match next. This
is a negative lookahead assertion. For example, is a negative lookahead assertion. For example,
\code{Isaac (?!Asimov)} will match 'Isaac~' only if it's \emph{not} \regexp{Isaac (?!Asimov)} will match \code{'Isaac~'} only if it's \emph{not}
followed by 'Asimov'. followed by \code{'Asimov'}.
\end{list} \end{list}
The special sequences consist of \samp{\e} and a character from the The special sequences consist of \character{\e} and a character from the
list below. If the ordinary character is not on the list, then the list below. If the ordinary character is not on the list, then the
resulting RE will match the second character. For example, resulting RE will match the second character. For example,
\code{\e\$} matches the character \samp{\$}. \regexp{\e\$} matches the character \character{\$}.
\begin{list}{}{\leftmargin \MyLeftMargin \labelwidth \MyLabelWidth} \begin{list}{}{\leftmargin \MyLeftMargin \labelwidth \MyLabelWidth}
% %
\item[\code{\e \var{number}}] Matches the contents of the group of the \item[\code{\e \var{number}}] Matches the contents of the group of the
same number. Groups are numbered starting from 1. For example, same number. Groups are numbered starting from 1. For example,
\code{(.+) \e 1} matches 'the the' or '55 55', but not 'the end' (note \regexp{(.+) \e 1} matches \code{'the the'} or \code{'55 55'}, but not
\code{'the end'} (note
the space after the group). This special sequence can only be used to 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 \var{number} match one of the first 99 groups. If the first digit of \var{number}
is 0, or \var{number} is 3 octal digits long, it will not be interpreted is 0, or \var{number} is 3 octal digits long, it will not be interpreted
as a group match, but as the character with octal value \var{number}. as a group match, but as the character with octal value \var{number}.
Inside the \code{[} and \code{]} of a character class, all numeric Inside the \character{[} and \character{]} of a character class, all numeric
escapes are treated as characters. escapes are treated as characters.
% %
\item[\code{\e A}] Matches only at the start of the string. \item[\code{\e A}] Matches only at the start of the string.
@ -226,34 +238,34 @@ escapes are treated as characters.
beginning or end of a word. A word is defined as a sequence of beginning or end of a word. A word is defined as a sequence of
alphanumeric characters, so the end of a word is indicated by alphanumeric characters, so the end of a word is indicated by
whitespace or a non-alphanumeric character. Inside a character range, whitespace or a non-alphanumeric character. Inside a character range,
\code{\e b} represents the backspace character, for compatibility with \regexp{\e b} represents the backspace character, for compatibility with
Python's string literals. Python's string literals.
% %
\item[\code{\e B}] Matches the empty string, but only when it is \item[\code{\e B}] Matches the empty string, but only when it is
\emph{not} at the beginning or end of a word. \emph{not} at the beginning or end of a word.
% %
\item[\code{\e d}]Matches any decimal digit; this is \item[\code{\e d}]Matches any decimal digit; this is
equivalent to the set \code{[0-9]}. equivalent to the set \regexp{[0-9]}.
% %
\item[\code{\e D}]Matches any non-digit character; this is \item[\code{\e D}]Matches any non-digit character; this is
equivalent to the set \code{[\^0-9]}. equivalent to the set \regexp{[\^0-9]}.
% %
\item[\code{\e s}]Matches any whitespace character; this is \item[\code{\e s}]Matches any whitespace character; this is
equivalent to the set \code{[ \e t\e n\e r\e f\e v]}. equivalent to the set \regexp{[ \e t\e n\e r\e f\e v]}.
% %
\item[\code{\e S}]Matches any non-whitespace character; this is \item[\code{\e S}]Matches any non-whitespace character; this is
equivalent to the set \code{[\^\ \e t\e n\e r\e f\e v]}. equivalent to the set \regexp{[\^\ \e t\e n\e r\e f\e v]}.
% %
\item[\code{\e w}]When the \constant{LOCALE} flag is not specified, \item[\code{\e w}]When the \constant{LOCALE} flag is not specified,
matches any alphanumeric character; this is equivalent to the set matches any alphanumeric character; this is equivalent to the set
\code{[a-zA-Z0-9_]}. With \constant{LOCALE}, it will match the set \regexp{[a-zA-Z0-9_]}. With \constant{LOCALE}, it will match the set
\code{[0-9_]} plus whatever characters are defined as letters for the \regexp{[0-9_]} plus whatever characters are defined as letters for the
current locale. current locale.
% %
\item[\code{\e W}]When the \constant{LOCALE} flag is not specified, \item[\code{\e W}]When the \constant{LOCALE} flag is not specified,
matches any non-alphanumeric character; this is equivalent to the set matches any non-alphanumeric character; this is equivalent to the set
\code{[\^a-zA-Z0-9_]}. With \constant{LOCALE}, it will match any \regexp{[\^a-zA-Z0-9_]}. With \constant{LOCALE}, it will match any
character not in the set \code{[0-9_]}, and not defined as a letter character not in the set \regexp{[0-9_]}, and not defined as a letter
for the current locale. for the current locale.
\item[\code{\e Z}]Matches only at the end of the string. \item[\code{\e Z}]Matches only at the end of the string.
@ -301,42 +313,44 @@ expression will be used several times in a single program.
\begin{datadesc}{I} \begin{datadesc}{I}
\dataline{IGNORECASE} \dataline{IGNORECASE}
Perform case-insensitive matching; expressions like \code{[A-Z]} will match Perform case-insensitive matching; expressions like \regexp{[A-Z]} will match
lowercase letters, too. This is not affected by the current locale. lowercase letters, too. This is not affected by the current locale.
\end{datadesc} \end{datadesc}
\begin{datadesc}{L} \begin{datadesc}{L}
\dataline{LOCALE} \dataline{LOCALE}
Make \code{\e w}, \code{\e W}, \code{\e b}, Make \regexp{\e w}, \regexp{\e W}, \regexp{\e b},
\code{\e B}, dependent on the current locale. \regexp{\e B}, dependent on the current locale.
\end{datadesc} \end{datadesc}
\begin{datadesc}{M} \begin{datadesc}{M}
\dataline{MULTILINE} \dataline{MULTILINE}
When specified, the pattern character \code{\^} matches at the When specified, the pattern character \character{\^} matches at the
beginning of the string and at the beginning of each line beginning of the string and at the beginning of each line
(immediately following each newline); and the pattern character (immediately following each newline); and the pattern character
\code{\$} matches at the end of the string and at the end of each line \character{\$} matches at the end of the string and at the end of each line
(immediately preceding each newline). (immediately preceding each newline).
By default, \code{\^} matches only at the beginning of the string, and By default, \character{\^} matches only at the beginning of the string, and
\code{\$} only at the end of the string and immediately before the \character{\$} only at the end of the string and immediately before the
newline (if any) at the end of the string. newline (if any) at the end of the string.
\end{datadesc} \end{datadesc}
\begin{datadesc}{S} \begin{datadesc}{S}
\dataline{DOTALL} \dataline{DOTALL}
Make the \code{.} special character match any character at all, including a Make the \character{.} special character match any character at all, including a
newline; without this flag, \code{.} will match anything \emph{except} newline; without this flag, \character{.} will match anything \emph{except}
a newline. a newline.
\end{datadesc} \end{datadesc}
\begin{datadesc}{X} \begin{datadesc}{X}
\dataline{VERBOSE} \dataline{VERBOSE}
Ignore whitespace within the pattern 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 except when in a character class or preceded by an unescaped
backslash, and, when a line contains a \code{\#} neither in a character backslash, and, when a line contains a \character{\#} neither in a character
class or preceded by an unescaped backslash, all characters from the class or preceded by an unescaped backslash, all characters from the
leftmost such \code{\#} through the end of the line are ignored. leftmost such \character{\#} through the end of the line are ignored.
% XXX should add an example here
\end{datadesc} \end{datadesc}
@ -410,7 +424,7 @@ embedded modifiers in a pattern; e.g.
\samp{sub("(?i)b+", "x", "bbbb BBBB")} returns \code{'x x'}. \samp{sub("(?i)b+", "x", "bbbb BBBB")} returns \code{'x x'}.
The optional argument \var{count} is the maximum number of pattern The optional argument \var{count} is the maximum number of pattern
occurrences to be replaced; count must be a non-negative integer, and occurrences to be replaced; \var{count} must be a non-negative integer, and
the default value of 0 means to replace all occurrences. the default value of 0 means to replace all occurrences.
Empty matches for the pattern are replaced only when not adjacent to a Empty matches for the pattern are replaced only when not adjacent to a
@ -419,17 +433,17 @@ previous match, so \samp{sub('x*', '-', 'abc')} returns \code{'-a-b-c-'}.
If \var{repl} is a string, any backslash escapes in it are processed. If \var{repl} is a string, any backslash escapes in it are processed.
That is, \samp{\e n} is converted to a single newline character, That is, \samp{\e n} is converted to a single newline character,
\samp{\e r} is converted to a linefeed, and so forth. Unknown escapes \samp{\e r} is converted to a linefeed, and so forth. Unknown escapes
such as \samp{\e j} are left alone. Backreferences, such as \samp{\e 6} are such as \samp{\e j} are left alone. Backreferences, such as \samp{\e 6}, are
replaced with the substring matched by group 6 in the pattern. replaced with the substring matched by group 6 in the pattern.
In addition to character escapes and backreferences as described In addition to character escapes and backreferences as described
above, \samp{\e g<name>} will use the substring matched by the group above, \samp{\e g<name>} will use the substring matched by the group
named \samp{name}, as defined by the \samp{(?P<name>...)} syntax. named \samp{name}, as defined by the \regexp{(?P<name>...)} syntax.
\samp{\e g<number>} uses the corresponding group number; \samp{\e \samp{\e g<number>} uses the corresponding group number; \samp{\e
g<2>} is therefore equivalent to \samp{\e 2}, but isn't ambiguous in a g<2>} is therefore equivalent to \samp{\e 2}, but isn't ambiguous in a
replacement such as \samp{\e g<2>0}. \samp{\e 20} would be replacement such as \samp{\e g<2>0}. \samp{\e 20} would be
interpreted as a reference to group 20, not a reference to group 2 interpreted as a reference to group 20, not a reference to group 2
followed by the literal character \samp{0}. followed by the literal character \character{0}.
\end{funcdesc} \end{funcdesc}
\begin{funcdesc}{subn}{pattern, repl, string\optional{, count\code{ = 0}}} \begin{funcdesc}{subn}{pattern, repl, string\optional{, count\code{ = 0}}}
@ -458,7 +472,7 @@ attributes:
The optional second parameter \var{pos} gives an index in the string The optional second parameter \var{pos} gives an index in the string
where the search is to start; it defaults to \code{0}. The where the search is to start; it defaults to \code{0}. The
\samp{\^} pattern character will match at the index where the \character{\^} pattern character will not match at the index where the
search is to start. search is to start.
The optional parameter \var{endpos} limits how far the string will The optional parameter \var{endpos} limits how far the string will
@ -500,7 +514,7 @@ The flags argument used when the regex object was compiled, or
\begin{memberdesc}[RegexObject]{groupindex} \begin{memberdesc}[RegexObject]{groupindex}
A dictionary mapping any symbolic group names defined by A dictionary mapping any symbolic group names defined by
\code{(?P<\var{id}>)} to group numbers. The dictionary is empty if no \regexp{(?P<\var{id}>)} to group numbers. The dictionary is empty if no
symbolic groups were used in the pattern. symbolic groups were used in the pattern.
\end{memberdesc} \end{memberdesc}
@ -528,7 +542,7 @@ the corresponding result is \code{None}. If a group is contained in a
part of the pattern that matched multiple times, the last match is part of the pattern that matched multiple times, the last match is
returned. returned.
If the regular expression uses the \code{(?P<\var{name}>...)} syntax, If the regular expression uses the \regexp{(?P<\var{name}>...)} syntax,
the \var{groupN} arguments may also be strings identifying groups by the \var{groupN} arguments may also be strings identifying groups by
their group name. If a string argument is not used as a group name in their group name. If a string argument is not used as a group name in
the pattern, an \exception{IndexError} exception is raised. the pattern, an \exception{IndexError} exception is raised.
@ -610,3 +624,4 @@ O'Reilly. The Python material in this book dates from before the
\module{re} module, but it covers writing good regular expression \module{re} module, but it covers writing good regular expression
patterns in great detail.} patterns in great detail.}
\end{seealso} \end{seealso}

221
Doc/libre.tex
View File

@ -4,25 +4,28 @@
\bimodindex{re} \bimodindex{re}
This module provides regular expression matching operations similar to This module provides regular expression matching operations similar to
those found in Perl. It's 8-bit clean: both patterns and strings may those found in Perl. It's 8-bit clean: the strings being processed
contain null bytes and characters whose high bit is set. It is always may contain both null bytes and characters whose high bit is set. Regular
expression patterns may not contain null bytes, but they may contain
characters with the high bit set. The \module{re} module is always
available. available.
Regular expressions use the backslash character (\samp{\e}) to Regular expressions use the backslash character (\character{\e}) to
indicate special forms or to allow special characters to be used indicate special forms or to allow special characters to be used
without invoking their special meaning. This collides with Python's without invoking their special meaning. This collides with Python's
usage of the same character for the same purpose in string literals; usage of the same character for the same purpose in string literals;
for example, to match a literal backslash, one might have to write for example, to match a literal backslash, one might have to write
\samp{\e\e\e\e} as the pattern string, because the regular expression \code{'\e\e\e\e'} as the pattern string, because the regular expression
must be \samp{\e\e}, and each backslash must be expressed as must be \samp{\e\e}, and each backslash must be expressed as
\samp{\e\e} inside a regular Python string literal. \samp{\e\e} inside a regular Python string literal.
The solution is to use Python's raw string notation for regular The solution is to use Python's raw string notation for regular
expression patterns; backslashes are not handled in any special way in expression patterns; backslashes are not handled in any special way in
a string literal prefixed with 'r'. So \code{r"\e n"} is a two a string literal prefixed with \character{r}. So \code{r"\e n"} is a
character string containing a backslash and the letter 'n', while two-character string containing \character{\e} and \character{n},
\code{"\e n"} is a one-character string containing a newline. Usually while \code{"\e n"} is a one-character string containing a newline.
patterns will be expressed in Python code using this raw string notation. Usually patterns will be expressed in Python code using this raw
string notation.
\subsection{Regular Expression Syntax} \subsection{Regular Expression Syntax}
@ -45,14 +48,14 @@ A brief explanation of the format of regular expressions follows.
%For further information and a gentler presentation, consult XXX somewhere. %For further information and a gentler presentation, consult XXX somewhere.
Regular expressions can contain both special and ordinary characters. Regular expressions can contain both special and ordinary characters.
Most ordinary characters, like \samp{A}, \samp{a}, or \samp{0}, Most ordinary characters, like \character{A}, \character{a}, or \character{0},
are the simplest regular expressions; they simply match themselves. are the simplest regular expressions; they simply match themselves.
You can concatenate ordinary characters, so \samp{last} matches the You can concatenate ordinary characters, so \regexp{last} matches the
characters 'last'. (In the rest of this section, we'll write RE's in string \code{'last'}. (In the rest of this section, we'll write RE's in
\code{this special font}, usually without quotes, and strings to be \regexp{this special style}, usually without quotes, and strings to be
matched 'in single quotes'.) matched \code{'in single quotes'}.)
Some characters, like \samp{|} or \samp{(}, are special. Special Some characters, like \character{|} or \character{(}, are special. Special
characters either stand for classes of ordinary characters, or affect characters either stand for classes of ordinary characters, or affect
how the regular expressions around them are interpreted. how the regular expressions around them are interpreted.
@ -61,56 +64,58 @@ The special characters are:
\newcommand{\MyLeftMargin}{0.7in} \newcommand{\MyLeftMargin}{0.7in}
\newcommand{\MyLabelWidth}{0.65in} \newcommand{\MyLabelWidth}{0.65in}
\begin{list}{}{\leftmargin \MyLeftMargin \labelwidth \MyLabelWidth} \begin{list}{}{\leftmargin \MyLeftMargin \labelwidth \MyLabelWidth}
\item[\code{.}] (Dot.) In the default mode, this matches any \item[\character{.}] (Dot.) In the default mode, this matches any
character except a newline. If the \constant{DOTALL} flag has been character except a newline. If the \constant{DOTALL} flag has been
specified, this matches any character including a newline. specified, this matches any character including a newline.
% %
\item[\code{\^}] (Caret.) Matches the start of the string, and in \item[\character{\^}] (Caret.) Matches the start of the string, and in
\constant{MULTILINE} mode also immediately after each newline. \constant{MULTILINE} mode also matches immediately after each newline.
% %
\item[\code{\$}] Matches the end of the string, and in \item[\character{\$}] Matches the end of the string, and in
\constant{MULTILINE} mode also matches before a newline. \constant{MULTILINE} mode also matches before a newline.
\code{foo} matches both 'foo' and 'foobar', while the regular \regexp{foo} matches both 'foo' and 'foobar', while the regular
expression \code{foo\$} matches only 'foo'. expression \regexp{foo\$} matches only 'foo'.
% %
\item[\code{*}] Causes the resulting RE to \item[\character{*}] Causes the resulting RE to
match 0 or more repetitions of the preceding RE, as many repetitions match 0 or more repetitions of the preceding RE, as many repetitions
as are possible. \code{ab*} will as are possible. \regexp{ab*} will
match 'a', 'ab', or 'a' followed by any number of 'b's. match 'a', 'ab', or 'a' followed by any number of 'b's.
% %
\item[\code{+}] Causes the \item[\character{+}] Causes the
resulting RE to match 1 or more repetitions of the preceding RE. resulting RE to match 1 or more repetitions of the preceding RE.
\code{ab+} will match 'a' followed by any non-zero number of 'b's; it \regexp{ab+} will match 'a' followed by any non-zero number of 'b's; it
will not match just 'a'. will not match just 'a'.
% %
\item[\code{?}] Causes the resulting RE to \item[\character{?}] Causes the resulting RE to
match 0 or 1 repetitions of the preceding RE. \code{ab?} will match 0 or 1 repetitions of the preceding RE. \regexp{ab?} will
match either 'a' or 'ab'. match either 'a' or 'ab'.
\item[\code{*?}, \code{+?}, \code{??}] The \code{*}, \code{+}, and \item[\code{*?}, \code{+?}, \code{??}] The \character{*}, \character{+}, and
\code{?} qualifiers are all \dfn{greedy}; they match as much text as \character{?} qualifiers are all \dfn{greedy}; they match as much text as
possible. Sometimes this behaviour isn't desired; if the RE possible. Sometimes this behaviour isn't desired; if the RE
\code{<.*>} is matched against \code{<H1>title</H1>}, it will match the \regexp{<.*>} is matched against \code{'<H1>title</H1>'}, it will match the
entire string, and not just \code{<H1>}. entire string, and not just \code{'<H1>'}.
Adding \code{?} after the qualifier makes it perform the match in Adding \character{?} after the qualifier makes it perform the match in
\dfn{non-greedy} or \dfn{minimal} fashion; as few characters as \dfn{non-greedy} or \dfn{minimal} fashion; as \emph{few} characters as
possible will be matched. Using \code{.*?} in the previous possible will be matched. Using \regexp{.*?} in the previous
expression will match only \code{<H1>}. expression will match only \code{'<H1>'}.
% %
\item[\code{\{\var{m},\var{n}\}}] Causes the resulting RE to match from \item[\code{\{\var{m},\var{n}\}}] Causes the resulting RE to match from
\var{m} to \var{n} repetitions of the preceding RE, attempting to \var{m} to \var{n} repetitions of the preceding RE, attempting to
match as many repetitions as possible. For example, \code{a\{3,5\}} match as many repetitions as possible. For example, \regexp{a\{3,5\}}
will match from 3 to 5 'a' characters. will match from 3 to 5 \character{a} characters. Omitting \var{m} is the same
as specifying 0 for the lower bound; omitting \var{n} specifies an
infinite upper bound.
% %
\item[\code{\{\var{m},\var{n}\}?}] Causes the resulting RE to \item[\code{\{\var{m},\var{n}\}?}] Causes the resulting RE to
match from \var{m} to \var{n} repetitions of the preceding RE, match from \var{m} to \var{n} repetitions of the preceding RE,
attempting to match as \emph{few} repetitions as possible. This is attempting to match as \emph{few} repetitions as possible. This is
the non-greedy version of the previous qualifier. For example, on the the non-greedy version of the previous qualifier. For example, on the
6-character string 'aaaaaa', \code{a\{3,5\}} will match 5 'a' 6-character string \code{'aaaaaa'}, \regexp{a\{3,5\}} will match 5 \character{a}
characters, while \code{a\{3,5\}?} will only match 3 characters. characters, while \regexp{a\{3,5\}?} will only match 3 characters.
% %
\item[\code{\e}] Either escapes special characters (permitting you to match \item[\character{\e}] Either escapes special characters (permitting you to match
characters like '*?+\&\$'), or signals a special sequence; special characters like \character{*}, \character{?}, and so forth), or
sequences are discussed below. signals a special sequence; special sequences are discussed below.
If you're not using a raw string to If you're not using a raw string to
express the pattern, remember that Python also uses the express the pattern, remember that Python also uses the
@ -124,42 +129,47 @@ simplest expressions.
% %
\item[\code{[]}] Used to indicate a set of characters. Characters can \item[\code{[]}] Used to indicate a set of characters. Characters can
be listed individually, or a range of characters can be indicated by be listed individually, or a range of characters can be indicated by
giving two characters and separating them by a '-'. Special giving two characters and separating them by a \character{-}. Special
characters are not active inside sets. For example, \code{[akm\$]} characters are not active inside sets. For example, \regexp{[akm\$]}
will match any of the characters \character{a}, \character{k}, will match any of the characters \character{a}, \character{k},
\character{m}, or \character{\$}; \code{[a-z]} \character{m}, or \character{\$}; \regexp{[a-z]}
will match any lowercase letter and \code{[a-zA-Z0-9]} matches any will match any lowercase letter, and \code{[a-zA-Z0-9]} matches any
letter or digit. Character classes such as \code{\e w} or \code {\e letter or digit. Character classes such as \code{\e w} or \code {\e
S} (defined below) are also acceptable inside a range. If you want to S} (defined below) are also acceptable inside a range. If you want to
include a \samp{]} or a \samp{-} inside a set, precede it with a include a \character{]} or a \character{-} inside a set, precede it with a
backslash. backslash, or place it as the first character. The
pattern \regexp{[]]} will match \code{']'}, for example.
You can match the characters not within a range by \dfn{complementing}
the set. This is indicated by including a
\character{\^} as the first character of the set; \character{\^} elsewhere will
simply match the \character{\^} character. For example, \regexp{[\^5]}
will match any character except \character{5}.
Characters \emph{not} within a range can be matched by including a
\code{\^} as the first character of the set; \code{\^} elsewhere will
simply match the \samp{\^} character.
% %
\item[\code{|}]\code{A|B}, where A and B can be arbitrary REs, \item[\character{|}]\code{A|B}, where A and B can be arbitrary REs,
creates a regular expression that will match either A or B. This can creates a regular expression that will match either A or B. This can
be used inside groups (see below) as well. To match a literal \samp{|}, be used inside groups (see below) as well. To match a literal \character{|},
use \code{\e|}, or enclose it inside a character class, like \code{[|]}. use \regexp{\e|}, or enclose it inside a character class, as in \regexp{[|]}.
% %
\item[\code{(...)}] Matches whatever regular expression is inside the \item[\code{(...)}] Matches whatever regular expression is inside the
parentheses, and indicates the start and end of a group; the contents 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 of a group can be retrieved after a match has been performed, and can
be matched later in the string with the \code{\e \var{number}} special be matched later in the string with the \regexp{\e \var{number}} special
sequence, described below. To match the literals '(' or ')', sequence, described below. To match the literals \character{(} or \character{')},
use \code{\e(} or \code{\e)}, or enclose them inside a character use \regexp{\e(} or \regexp{\e)}, or enclose them inside a character
class: \code{[(] [)]}. class: \regexp{[(] [)]}.
% %
\item[\code{(?...)}] This is an extension notation (a '?' following a \item[\code{(?...)}] This is an extension notation (a \character{?} following a
'(' is not meaningful otherwise). The first character after the '?' \character{(} is not meaningful otherwise). The first character after
the \character{?}
determines what the meaning and further syntax of the construct is. determines what the meaning and further syntax of the construct is.
Extensions usually do not create a new group; Extensions usually do not create a new group;
\code{(?P<\var{name}>...)} is the only exception to this rule. \regexp{(?P<\var{name}>...)} is the only exception to this rule.
Following are the currently supported extensions. Following are the currently supported extensions.
% %
\item[\code{(?iLmsx)}] (One or more letters from the set \samp{i}, \item[\code{(?iLmsx)}] (One or more letters from the set \character{i},
\samp{L}, \samp{m}, \samp{s}, \samp{x}.) The group matches \character{L}, \character{m}, \character{s}, \character{x}.) The group matches
the empty string; the letters set the corresponding flags the empty string; the letters set the corresponding flags
(\constant{re.I}, \constant{re.L}, \constant{re.M}, \constant{re.S}, (\constant{re.I}, \constant{re.L}, \constant{re.M}, \constant{re.S},
\constant{re.X}) for the entire regular expression. This is useful if \constant{re.X}) for the entire regular expression. This is useful if
@ -167,7 +177,8 @@ you wish to include the flags as part of the regular expression, instead
of passing a \var{flag} argument to the \function{compile()} function. of passing a \var{flag} argument to the \function{compile()} function.
% %
\item[\code{(?:...)}] A non-grouping version of regular parentheses. \item[\code{(?:...)}] A non-grouping version of regular parentheses.
Matches whatever's inside the parentheses, but the substring matched by the Matches whatever regular expression is inside the parentheses, but the
substring matched by the
group \emph{cannot} be retrieved after performing a match or group \emph{cannot} be retrieved after performing a match or
referenced later in the pattern. referenced later in the pattern.
% %
@ -179,10 +190,10 @@ named. So the group named 'id' in the example above can also be
referenced as the numbered group 1. referenced as the numbered group 1.
For example, if the pattern is For example, if the pattern is
\code{(?P<id>[a-zA-Z_]\e w*)}, the group can be referenced by its \regexp{(?P<id>[a-zA-Z_]\e w*)}, the group can be referenced by its
name in arguments to methods of match objects, such as \code{m.group('id')} name in arguments to methods of match objects, such as \code{m.group('id')}
or \code{m.end('id')}, and also by name in pattern text or \code{m.end('id')}, and also by name in pattern text
(e.g. \code{(?P=id)}) and replacement text (e.g. \code{\e g<id>}). (e.g. \regexp{(?P=id)}) and replacement text (e.g. \code{\e g<id>}).
% %
\item[\code{(?P=\var{name})}] Matches whatever text was matched by the \item[\code{(?P=\var{name})}] Matches whatever text was matched by the
earlier group named \var{name}. earlier group named \var{name}.
@ -190,34 +201,35 @@ earlier group named \var{name}.
\item[\code{(?\#...)}] A comment; the contents of the parentheses are \item[\code{(?\#...)}] A comment; the contents of the parentheses are
simply ignored. simply ignored.
% %
\item[\code{(?=...)}] Matches if \code{...} matches next, but doesn't \item[\code{(?=...)}] Matches if \regexp{...} matches next, but doesn't
consume any of the string. This is called a lookahead assertion. For consume any of the string. This is called a lookahead assertion. For
example, \code{Isaac (?=Asimov)} will match 'Isaac~' only if it's example, \regexp{Isaac (?=Asimov)} will match \code{'Isaac~'} only if it's
followed by 'Asimov'. followed by \code{'Asimov'}.
% %
\item[\code{(?!...)}] Matches if \code{...} doesn't match next. This \item[\code{(?!...)}] Matches if \regexp{...} doesn't match next. This
is a negative lookahead assertion. For example, is a negative lookahead assertion. For example,
\code{Isaac (?!Asimov)} will match 'Isaac~' only if it's \emph{not} \regexp{Isaac (?!Asimov)} will match \code{'Isaac~'} only if it's \emph{not}
followed by 'Asimov'. followed by \code{'Asimov'}.
\end{list} \end{list}
The special sequences consist of \samp{\e} and a character from the The special sequences consist of \character{\e} and a character from the
list below. If the ordinary character is not on the list, then the list below. If the ordinary character is not on the list, then the
resulting RE will match the second character. For example, resulting RE will match the second character. For example,
\code{\e\$} matches the character \samp{\$}. \regexp{\e\$} matches the character \character{\$}.
\begin{list}{}{\leftmargin \MyLeftMargin \labelwidth \MyLabelWidth} \begin{list}{}{\leftmargin \MyLeftMargin \labelwidth \MyLabelWidth}
% %
\item[\code{\e \var{number}}] Matches the contents of the group of the \item[\code{\e \var{number}}] Matches the contents of the group of the
same number. Groups are numbered starting from 1. For example, same number. Groups are numbered starting from 1. For example,
\code{(.+) \e 1} matches 'the the' or '55 55', but not 'the end' (note \regexp{(.+) \e 1} matches \code{'the the'} or \code{'55 55'}, but not
\code{'the end'} (note
the space after the group). This special sequence can only be used to 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 \var{number} match one of the first 99 groups. If the first digit of \var{number}
is 0, or \var{number} is 3 octal digits long, it will not be interpreted is 0, or \var{number} is 3 octal digits long, it will not be interpreted
as a group match, but as the character with octal value \var{number}. as a group match, but as the character with octal value \var{number}.
Inside the \code{[} and \code{]} of a character class, all numeric Inside the \character{[} and \character{]} of a character class, all numeric
escapes are treated as characters. escapes are treated as characters.
% %
\item[\code{\e A}] Matches only at the start of the string. \item[\code{\e A}] Matches only at the start of the string.
@ -226,34 +238,34 @@ escapes are treated as characters.
beginning or end of a word. A word is defined as a sequence of beginning or end of a word. A word is defined as a sequence of
alphanumeric characters, so the end of a word is indicated by alphanumeric characters, so the end of a word is indicated by
whitespace or a non-alphanumeric character. Inside a character range, whitespace or a non-alphanumeric character. Inside a character range,
\code{\e b} represents the backspace character, for compatibility with \regexp{\e b} represents the backspace character, for compatibility with
Python's string literals. Python's string literals.
% %
\item[\code{\e B}] Matches the empty string, but only when it is \item[\code{\e B}] Matches the empty string, but only when it is
\emph{not} at the beginning or end of a word. \emph{not} at the beginning or end of a word.
% %
\item[\code{\e d}]Matches any decimal digit; this is \item[\code{\e d}]Matches any decimal digit; this is
equivalent to the set \code{[0-9]}. equivalent to the set \regexp{[0-9]}.
% %
\item[\code{\e D}]Matches any non-digit character; this is \item[\code{\e D}]Matches any non-digit character; this is
equivalent to the set \code{[\^0-9]}. equivalent to the set \regexp{[\^0-9]}.
% %
\item[\code{\e s}]Matches any whitespace character; this is \item[\code{\e s}]Matches any whitespace character; this is
equivalent to the set \code{[ \e t\e n\e r\e f\e v]}. equivalent to the set \regexp{[ \e t\e n\e r\e f\e v]}.
% %
\item[\code{\e S}]Matches any non-whitespace character; this is \item[\code{\e S}]Matches any non-whitespace character; this is
equivalent to the set \code{[\^\ \e t\e n\e r\e f\e v]}. equivalent to the set \regexp{[\^\ \e t\e n\e r\e f\e v]}.
% %
\item[\code{\e w}]When the \constant{LOCALE} flag is not specified, \item[\code{\e w}]When the \constant{LOCALE} flag is not specified,
matches any alphanumeric character; this is equivalent to the set matches any alphanumeric character; this is equivalent to the set
\code{[a-zA-Z0-9_]}. With \constant{LOCALE}, it will match the set \regexp{[a-zA-Z0-9_]}. With \constant{LOCALE}, it will match the set
\code{[0-9_]} plus whatever characters are defined as letters for the \regexp{[0-9_]} plus whatever characters are defined as letters for the
current locale. current locale.
% %
\item[\code{\e W}]When the \constant{LOCALE} flag is not specified, \item[\code{\e W}]When the \constant{LOCALE} flag is not specified,
matches any non-alphanumeric character; this is equivalent to the set matches any non-alphanumeric character; this is equivalent to the set
\code{[\^a-zA-Z0-9_]}. With \constant{LOCALE}, it will match any \regexp{[\^a-zA-Z0-9_]}. With \constant{LOCALE}, it will match any
character not in the set \code{[0-9_]}, and not defined as a letter character not in the set \regexp{[0-9_]}, and not defined as a letter
for the current locale. for the current locale.
\item[\code{\e Z}]Matches only at the end of the string. \item[\code{\e Z}]Matches only at the end of the string.
@ -301,42 +313,44 @@ expression will be used several times in a single program.
\begin{datadesc}{I} \begin{datadesc}{I}
\dataline{IGNORECASE} \dataline{IGNORECASE}
Perform case-insensitive matching; expressions like \code{[A-Z]} will match Perform case-insensitive matching; expressions like \regexp{[A-Z]} will match
lowercase letters, too. This is not affected by the current locale. lowercase letters, too. This is not affected by the current locale.
\end{datadesc} \end{datadesc}
\begin{datadesc}{L} \begin{datadesc}{L}
\dataline{LOCALE} \dataline{LOCALE}
Make \code{\e w}, \code{\e W}, \code{\e b}, Make \regexp{\e w}, \regexp{\e W}, \regexp{\e b},
\code{\e B}, dependent on the current locale. \regexp{\e B}, dependent on the current locale.
\end{datadesc} \end{datadesc}
\begin{datadesc}{M} \begin{datadesc}{M}
\dataline{MULTILINE} \dataline{MULTILINE}
When specified, the pattern character \code{\^} matches at the When specified, the pattern character \character{\^} matches at the
beginning of the string and at the beginning of each line beginning of the string and at the beginning of each line
(immediately following each newline); and the pattern character (immediately following each newline); and the pattern character
\code{\$} matches at the end of the string and at the end of each line \character{\$} matches at the end of the string and at the end of each line
(immediately preceding each newline). (immediately preceding each newline).
By default, \code{\^} matches only at the beginning of the string, and By default, \character{\^} matches only at the beginning of the string, and
\code{\$} only at the end of the string and immediately before the \character{\$} only at the end of the string and immediately before the
newline (if any) at the end of the string. newline (if any) at the end of the string.
\end{datadesc} \end{datadesc}
\begin{datadesc}{S} \begin{datadesc}{S}
\dataline{DOTALL} \dataline{DOTALL}
Make the \code{.} special character match any character at all, including a Make the \character{.} special character match any character at all, including a
newline; without this flag, \code{.} will match anything \emph{except} newline; without this flag, \character{.} will match anything \emph{except}
a newline. a newline.
\end{datadesc} \end{datadesc}
\begin{datadesc}{X} \begin{datadesc}{X}
\dataline{VERBOSE} \dataline{VERBOSE}
Ignore whitespace within the pattern 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 except when in a character class or preceded by an unescaped
backslash, and, when a line contains a \code{\#} neither in a character backslash, and, when a line contains a \character{\#} neither in a character
class or preceded by an unescaped backslash, all characters from the class or preceded by an unescaped backslash, all characters from the
leftmost such \code{\#} through the end of the line are ignored. leftmost such \character{\#} through the end of the line are ignored.
% XXX should add an example here
\end{datadesc} \end{datadesc}
@ -410,7 +424,7 @@ embedded modifiers in a pattern; e.g.
\samp{sub("(?i)b+", "x", "bbbb BBBB")} returns \code{'x x'}. \samp{sub("(?i)b+", "x", "bbbb BBBB")} returns \code{'x x'}.
The optional argument \var{count} is the maximum number of pattern The optional argument \var{count} is the maximum number of pattern
occurrences to be replaced; count must be a non-negative integer, and occurrences to be replaced; \var{count} must be a non-negative integer, and
the default value of 0 means to replace all occurrences. the default value of 0 means to replace all occurrences.
Empty matches for the pattern are replaced only when not adjacent to a Empty matches for the pattern are replaced only when not adjacent to a
@ -419,17 +433,17 @@ previous match, so \samp{sub('x*', '-', 'abc')} returns \code{'-a-b-c-'}.
If \var{repl} is a string, any backslash escapes in it are processed. If \var{repl} is a string, any backslash escapes in it are processed.
That is, \samp{\e n} is converted to a single newline character, That is, \samp{\e n} is converted to a single newline character,
\samp{\e r} is converted to a linefeed, and so forth. Unknown escapes \samp{\e r} is converted to a linefeed, and so forth. Unknown escapes
such as \samp{\e j} are left alone. Backreferences, such as \samp{\e 6} are such as \samp{\e j} are left alone. Backreferences, such as \samp{\e 6}, are
replaced with the substring matched by group 6 in the pattern. replaced with the substring matched by group 6 in the pattern.
In addition to character escapes and backreferences as described In addition to character escapes and backreferences as described
above, \samp{\e g<name>} will use the substring matched by the group above, \samp{\e g<name>} will use the substring matched by the group
named \samp{name}, as defined by the \samp{(?P<name>...)} syntax. named \samp{name}, as defined by the \regexp{(?P<name>...)} syntax.
\samp{\e g<number>} uses the corresponding group number; \samp{\e \samp{\e g<number>} uses the corresponding group number; \samp{\e
g<2>} is therefore equivalent to \samp{\e 2}, but isn't ambiguous in a g<2>} is therefore equivalent to \samp{\e 2}, but isn't ambiguous in a
replacement such as \samp{\e g<2>0}. \samp{\e 20} would be replacement such as \samp{\e g<2>0}. \samp{\e 20} would be
interpreted as a reference to group 20, not a reference to group 2 interpreted as a reference to group 20, not a reference to group 2
followed by the literal character \samp{0}. followed by the literal character \character{0}.
\end{funcdesc} \end{funcdesc}
\begin{funcdesc}{subn}{pattern, repl, string\optional{, count\code{ = 0}}} \begin{funcdesc}{subn}{pattern, repl, string\optional{, count\code{ = 0}}}
@ -458,7 +472,7 @@ attributes:
The optional second parameter \var{pos} gives an index in the string The optional second parameter \var{pos} gives an index in the string
where the search is to start; it defaults to \code{0}. The where the search is to start; it defaults to \code{0}. The
\samp{\^} pattern character will match at the index where the \character{\^} pattern character will not match at the index where the
search is to start. search is to start.
The optional parameter \var{endpos} limits how far the string will The optional parameter \var{endpos} limits how far the string will
@ -500,7 +514,7 @@ The flags argument used when the regex object was compiled, or
\begin{memberdesc}[RegexObject]{groupindex} \begin{memberdesc}[RegexObject]{groupindex}
A dictionary mapping any symbolic group names defined by A dictionary mapping any symbolic group names defined by
\code{(?P<\var{id}>)} to group numbers. The dictionary is empty if no \regexp{(?P<\var{id}>)} to group numbers. The dictionary is empty if no
symbolic groups were used in the pattern. symbolic groups were used in the pattern.
\end{memberdesc} \end{memberdesc}
@ -528,7 +542,7 @@ the corresponding result is \code{None}. If a group is contained in a
part of the pattern that matched multiple times, the last match is part of the pattern that matched multiple times, the last match is
returned. returned.
If the regular expression uses the \code{(?P<\var{name}>...)} syntax, If the regular expression uses the \regexp{(?P<\var{name}>...)} syntax,
the \var{groupN} arguments may also be strings identifying groups by the \var{groupN} arguments may also be strings identifying groups by
their group name. If a string argument is not used as a group name in their group name. If a string argument is not used as a group name in
the pattern, an \exception{IndexError} exception is raised. the pattern, an \exception{IndexError} exception is raised.
@ -610,3 +624,4 @@ O'Reilly. The Python material in this book dates from before the
\module{re} module, but it covers writing good regular expression \module{re} module, but it covers writing good regular expression
patterns in great detail.} patterns in great detail.}
\end{seealso} \end{seealso}