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Fred Drake 1998-09-10 20:21:00 +00:00
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Doc/lib/libre.tex
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@ -33,8 +33,7 @@ while \code{"\e n"} is a one-character string containing a newline.
Usually patterns will be expressed in Python code using this raw Usually patterns will be expressed in Python code using this raw
string notation. string notation.
\subsection{Regular Expression Syntax} \subsection{Regular Expression Syntax \label{re-syntax}}
\label{re-syntax}
A regular expression (or RE) specifies a set of strings that matches 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 it; the functions in this module let you check if a particular string
@ -70,29 +69,31 @@ The special characters are:
% define these since they're used twice: % define these since they're used twice:
\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[\character{.}] (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[\character{\^}] (Caret.) Matches the start of the string, and in \item[\character{\^}] (Caret.) Matches the start of the string, and in
\constant{MULTILINE} mode also matches immediately after each newline. \constant{MULTILINE} mode also matches immediately after each newline.
%
\item[\character{\$}] 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.
\regexp{foo} matches both 'foo' and 'foobar', while the regular \regexp{foo} matches both 'foo' and 'foobar', while the regular
expression \regexp{foo\$} matches only 'foo'. expression \regexp{foo\$} matches only 'foo'.
%
\item[\character{*}] 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. \regexp{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[\character{+}] 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.
\regexp{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[\character{?}] Causes the resulting RE to \item[\character{?}] Causes the resulting RE to
match 0 or 1 repetitions of the preceding RE. \regexp{ab?} will match 0 or 1 repetitions of the preceding RE. \regexp{ab?} will
match either 'a' or 'ab'. match either 'a' or 'ab'.
@ -105,24 +106,26 @@ Adding \character{?} after the qualifier makes it perform the match in
\dfn{non-greedy} or \dfn{minimal} fashion; as \emph{few} characters as \dfn{non-greedy} or \dfn{minimal} fashion; as \emph{few} characters as
possible will be matched. Using \regexp{.*?} 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, \regexp{a\{3,5\}} match as many repetitions as possible. For example, \regexp{a\{3,5\}}
will match from 3 to 5 \character{a} characters. Omitting \var{m} is the same 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 as specifying 0 for the lower bound; omitting \var{n} specifies an
infinite upper bound. 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 \code{'aaaaaa'}, \regexp{a\{3,5\}} will match 5 \character{a} 6-character string \code{'aaaaaa'}, \regexp{a\{3,5\}} will match 5
characters, while \regexp{a\{3,5\}?} will only match 3 characters. \character{a} characters, while \regexp{a\{3,5\}?} will only match 3
% characters.
\item[\character{\e}] Either escapes special characters (permitting you to match
characters like \character{*}, \character{?}, and so forth), or \item[\character{\e}] Either escapes special characters (permitting
signals a special sequence; special sequences are discussed below. you to match characters like \character{*}, \character{?}, and so
forth), or 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
@ -133,7 +136,7 @@ if Python would recognize the resulting sequence, the backslash should
be repeated twice. This is complicated and hard to understand, so be repeated twice. This is complicated and hard to understand, so
it's highly recommended that you use raw strings for all but the it's highly recommended that you use raw strings for all but the
simplest expressions. 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 \character{-}. Special giving two characters and separating them by a \character{-}. Special
@ -153,28 +156,27 @@ the set. This is indicated by including a
simply match the \character{\^} character. For example, \regexp{[\^5]} simply match the \character{\^} character. For example, \regexp{[\^5]}
will match any character except \character{5}. will match any character except \character{5}.
%
\item[\character{|}]\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 \character{|}, be used inside groups (see below) as well. To match a literal \character{|},
use \regexp{\e|}, or enclose it inside a character class, as in \regexp{[|]}. 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 \regexp{\e \var{number}} special be matched later in the string with the \regexp{\e \var{number}} special
sequence, described below. To match the literals \character{(} or \character{')}, sequence, described below. To match the literals \character{(} or
use \regexp{\e(} or \regexp{\e)}, or enclose them inside a character \character{')}, use \regexp{\e(} or \regexp{\e)}, or enclose them
class: \regexp{[(] [)]}. inside a character class: \regexp{[(] [)]}.
%
\item[\code{(?...)}] This is an extension notation (a \character{?} following a \item[\code{(?...)}] This is an extension notation (a \character{?}
\character{(} is not meaningful otherwise). The first character after following a \character{(} is not meaningful otherwise). The first
the \character{?} 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;
\regexp{(?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 \character{i}, \item[\code{(?iLmsx)}] (One or more letters from the set \character{i},
\character{L}, \character{m}, \character{s}, \character{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
@ -182,13 +184,13 @@ the empty string; the letters set the corresponding flags
\constant{re.X}) for the entire regular expression. This is useful if \constant{re.X}) for the entire regular expression. This is useful if
you wish to include the flags as part of the regular expression, instead 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 regular expression is inside the parentheses, but the Matches whatever regular expression is inside the parentheses, but the
substring matched by 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.
%
\item[\code{(?P<\var{name}>...)}] Similar to regular parentheses, but \item[\code{(?P<\var{name}>...)}] Similar to regular parentheses, but
the substring matched by the group is accessible via the symbolic group the substring matched by the group is accessible via the symbolic group
name \var{name}. Group names must be valid Python identifiers. A name \var{name}. Group names must be valid Python identifiers. A
@ -201,18 +203,18 @@ For example, if the pattern is
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. \regexp{(?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}.
%
\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 \regexp{...} 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, \regexp{Isaac (?=Asimov)} will match \code{'Isaac~'} only if it's example, \regexp{Isaac (?=Asimov)} will match \code{'Isaac~'} only if it's
followed by \code{'Asimov'}. followed by \code{'Asimov'}.
%
\item[\code{(?!...)}] Matches if \regexp{...} 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,
\regexp{Isaac (?!Asimov)} will match \code{'Isaac~'} only if it's \emph{not} \regexp{Isaac (?!Asimov)} will match \code{'Isaac~'} only if it's \emph{not}
@ -474,8 +476,7 @@ Perform the same operation as \function{sub()}, but return a tuple
\end{excdesc} \end{excdesc}
\subsection{Regular Expression Objects} \subsection{Regular Expression Objects \label{re-objects}}
\label{re-objects}
Compiled regular expression objects support the following methods and Compiled regular expression objects support the following methods and
attributes: attributes:
@ -547,8 +548,7 @@ The pattern string from which the regex object was compiled.
\end{memberdesc} \end{memberdesc}
\subsection{Match Objects} \subsection{Match Objects \label{match-objects}}
\label{match-objects}
\class{MatchObject} instances support the following methods and attributes: \class{MatchObject} instances support the following methods and attributes: