Usually patterns will be expressed in Python code using this raw
string notation.
-\subsection{Regular Expression Syntax}
-\label{re-syntax}
+\subsection{Regular Expression Syntax \label{re-syntax}}
A regular expression (or RE) specifies a set of strings that matches
it; the functions in this module let you check if a particular string
% define these since they're used twice:
\newcommand{\MyLeftMargin}{0.7in}
\newcommand{\MyLabelWidth}{0.65in}
+
\begin{list}{}{\leftmargin \MyLeftMargin \labelwidth \MyLabelWidth}
+
\item[\character{.}] (Dot.) In the default mode, this matches any
character except a newline. If the \constant{DOTALL} flag has been
specified, this matches any character including a newline.
-%
+
\item[\character{\^}] (Caret.) Matches the start of the string, and in
\constant{MULTILINE} mode also matches immediately after each newline.
-%
+
\item[\character{\$}] Matches the end of the string, and in
\constant{MULTILINE} mode also matches before a newline.
\regexp{foo} matches both 'foo' and 'foobar', while the regular
expression \regexp{foo\$} matches only 'foo'.
-%
+
\item[\character{*}] Causes the resulting RE to
match 0 or more repetitions of the preceding RE, as many repetitions
as are possible. \regexp{ab*} will
match 'a', 'ab', or 'a' followed by any number of 'b's.
-%
+
\item[\character{+}] Causes the
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
will not match just 'a'.
-%
+
\item[\character{?}] Causes the resulting RE to
match 0 or 1 repetitions of the preceding RE. \regexp{ab?} will
match either 'a' or 'ab'.
\dfn{non-greedy} or \dfn{minimal} fashion; as \emph{few} characters as
possible will be matched. Using \regexp{.*?} in the previous
expression will match only \code{'<H1>'}.
-%
+
\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
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
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
match from \var{m} to \var{n} repetitions of the preceding RE,
attempting to match as \emph{few} repetitions as possible. This is
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}
-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
-signals a special sequence; special sequences are discussed below.
+6-character string \code{'aaaaaa'}, \regexp{a\{3,5\}} will match 5
+\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 signals a special sequence; special sequences are discussed
+below.
If you're not using a raw string to
express the pattern, remember that Python also uses the
be repeated twice. This is complicated and hard to understand, so
it's highly recommended that you use raw strings for all but the
simplest expressions.
-%
+
\item[\code{[]}] Used to indicate a set of characters. Characters can
be listed individually, or a range of characters can be indicated by
giving two characters and separating them by a \character{-}. Special
simply match the \character{\^} character. For example, \regexp{[\^5]}
will match any character except \character{5}.
-%
\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
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{[|]}.
-%
+
\item[\code{(...)}] Matches whatever regular expression is inside the
parentheses, and indicates the start and end of a group; the contents
of a group can be retrieved after a match has been performed, and can
be matched later in the string with the \regexp{\e \var{number}} special
-sequence, described below. To match the literals \character{(} or \character{')},
-use \regexp{\e(} or \regexp{\e)}, or enclose them inside a character
-class: \regexp{[(] [)]}.
-%
-\item[\code{(?...)}] This is an extension notation (a \character{?} following a
-\character{(} is not meaningful otherwise). The first character after
-the \character{?}
+sequence, described below. To match the literals \character{(} or
+\character{')}, use \regexp{\e(} or \regexp{\e)}, or enclose them
+inside a character class: \regexp{[(] [)]}.
+
+\item[\code{(?...)}] This is an extension notation (a \character{?}
+following a \character{(} is not meaningful otherwise). The first
+character after the \character{?}
determines what the meaning and further syntax of the construct is.
Extensions usually do not create a new group;
\regexp{(?P<\var{name}>...)} is the only exception to this rule.
Following are the currently supported extensions.
-%
+
\item[\code{(?iLmsx)}] (One or more letters from the set \character{i},
\character{L}, \character{m}, \character{s}, \character{x}.) The group matches
the empty string; the letters set the corresponding flags
\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
of passing a \var{flag} argument to the \function{compile()} function.
-%
+
\item[\code{(?:...)}] A non-grouping version of regular parentheses.
Matches whatever regular expression is inside the parentheses, but the
substring matched by the
group \emph{cannot} be retrieved after performing a match or
referenced later in the pattern.
-%
+
\item[\code{(?P<\var{name}>...)}] Similar to regular parentheses, but
the substring matched by the group is accessible via the symbolic group
name \var{name}. Group names must be valid Python identifiers. A
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
(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
earlier group named \var{name}.
-%
+
\item[\code{(?\#...)}] A comment; the contents of the parentheses are
simply ignored.
-%
+
\item[\code{(?=...)}] Matches if \regexp{...} matches next, but doesn't
consume any of the string. This is called a lookahead assertion. For
example, \regexp{Isaac (?=Asimov)} will match \code{'Isaac~'} only if it's
followed by \code{'Asimov'}.
-%
+
\item[\code{(?!...)}] Matches if \regexp{...} doesn't match next. This
is a negative lookahead assertion. For example,
\regexp{Isaac (?!Asimov)} will match \code{'Isaac~'} only if it's \emph{not}
\end{excdesc}
-\subsection{Regular Expression Objects}
-\label{re-objects}
+\subsection{Regular Expression Objects \label{re-objects}}
Compiled regular expression objects support the following methods and
attributes:
\end{memberdesc}
-\subsection{Match Objects}
-\label{match-objects}
+\subsection{Match Objects \label{match-objects}}
\class{MatchObject} instances support the following methods and attributes:
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