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Diffstat (limited to 'Doc/lib/libre.tex')
| -rw-r--r-- | Doc/lib/libre.tex | 89 |
1 files changed, 47 insertions, 42 deletions
diff --git a/Doc/lib/libre.tex b/Doc/lib/libre.tex index 853372d..4cadac1 100644 --- a/Doc/lib/libre.tex +++ b/Doc/lib/libre.tex @@ -74,16 +74,16 @@ further information and a gentler presentation, consult the Regular Expression HOWTO, accessible from \url{http://www.python.org/doc/howto/}. Regular expressions can contain both special and ordinary characters. -Most ordinary characters, like \character{A}, \character{a}, or \character{0}, -are the simplest regular expressions; they simply match themselves. -You can concatenate ordinary characters, so \regexp{last} matches the -string \code{'last'}. (In the rest of this section, we'll write RE's in -\regexp{this special style}, usually without quotes, and strings to be -matched \code{'in single quotes'}.) +Most ordinary characters, like \character{A}, \character{a}, or +\character{0}, are the simplest regular expressions; they simply match +themselves. You can concatenate ordinary characters, so \regexp{last} +matches the string \code{'last'}. (In the rest of this section, we'll +write RE's in \regexp{this special style}, usually without quotes, and +strings to be matched \code{'in single quotes'}.) -Some characters, like \character{|} or \character{(}, are special. Special -characters either stand for classes of ordinary characters, or affect -how the regular expressions around them are interpreted. +Some characters, like \character{|} or \character{(}, are special. +Special characters either stand for classes of ordinary characters, or +affect how the regular expressions around them are interpreted. The special characters are: @@ -114,15 +114,16 @@ 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'. -\item[\code{*?}, \code{+?}, \code{??}] The \character{*}, \character{+}, and -\character{?} qualifiers are all \dfn{greedy}; they match as much text as -possible. Sometimes this behaviour isn't desired; if the RE -\regexp{<.*>} is matched against \code{'<H1>title</H1>'}, it will match the -entire string, and not just \code{'<H1>'}. -Adding \character{?} after the qualifier makes it perform the match in -\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{*?}, \code{+?}, \code{??}] The \character{*}, +\character{+}, and \character{?} qualifiers are all \dfn{greedy}; they +match as much text as possible. Sometimes this behaviour isn't +desired; if the RE \regexp{<.*>} is matched against +\code{'<H1>title</H1>'}, it will match the entire string, and not just +\code{'<H1>'}. Adding \character{?} after the qualifier makes it +perform the match in \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 @@ -167,10 +168,10 @@ 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}. +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}. \item[\character{|}]\code{A|B}, where A and B can be arbitrary REs, creates a regular expression that will match either A or B. An @@ -399,8 +400,9 @@ expression will be used several times in a single program. \begin{datadesc}{I} \dataline{IGNORECASE} -Perform case-insensitive matching; expressions like \regexp{[A-Z]} will match -lowercase letters, too. This is not affected by the current locale. +Perform case-insensitive matching; expressions like \regexp{[A-Z]} +will match lowercase letters, too. This is not affected by the +current locale. \end{datadesc} \begin{datadesc}{L} @@ -414,11 +416,11 @@ Make \regexp{\e w}, \regexp{\e W}, \regexp{\e b}, and When specified, the pattern character \character{\^} matches at the beginning of the string and at the beginning of each line (immediately following each newline); and the pattern character -\character{\$} matches at the end of the string and at the end of each line -(immediately preceding each newline). -By default, \character{\^} matches only at the beginning of the string, and -\character{\$} only at the end of the string and immediately before the -newline (if any) at the end of the string. +\character{\$} matches at the end of the string and at the end of each +line (immediately preceding each newline). By default, \character{\^} +matches only at the beginning of the string, and \character{\$} only +at the end of the string and immediately before the newline (if any) +at the end of the string. \end{datadesc} \begin{datadesc}{S} @@ -440,9 +442,10 @@ Make \regexp{\e w}, \regexp{\e W}, \regexp{\e b}, and This flag allows you to write regular expressions that look nicer. Whitespace within the pattern is ignored, except when in a character class or preceded by an unescaped -backslash, and, when a line contains a \character{\#} neither in a character -class or preceded by an unescaped backslash, all characters from the -leftmost such \character{\#} through the end of the line are ignored. +backslash, and, when a line contains a \character{\#} neither in a +character class or preceded by an unescaped backslash, all characters +from the leftmost such \character{\#} through the end of the line are +ignored. % XXX should add an example here \end{datadesc} @@ -521,17 +524,18 @@ embedded modifiers in a pattern; for example, \samp{sub("(?i)b+", "x", "bbbb BBBB")} returns \code{'x x'}. The optional argument \var{count} is the maximum number of pattern -occurrences to be replaced; \var{count} must be a non-negative integer, and -the default value of 0 means to replace all occurrences. +occurrences to be replaced; \var{count} must be a non-negative +integer, and the default value of 0 means to replace all occurrences. Empty matches for the pattern are replaced only when not adjacent to a -previous match, so \samp{sub('x*', '-', 'abc')} returns \code{'-a-b-c-'}. +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. 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 -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. +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. In addition to character escapes and backreferences as described above, \samp{\e g<name>} will use the substring matched by the group @@ -641,15 +645,16 @@ The pattern string from which the RE object was compiled. \subsection{Match Objects \label{match-objects}} -\class{MatchObject} instances support the following methods and attributes: +\class{MatchObject} instances support the following methods and +attributes: \begin{methoddesc}[MatchObject]{expand}{template} Return the string obtained by doing backslash substitution on the template string \var{template}, as done by the \method{sub()} method. Escapes such as \samp{\e n} are converted to the appropriate -characters, and numeric backreferences (\samp{\e 1}, \samp{\e 2}) and named -backreferences (\samp{\e g<1>}, \samp{\e g<name>}) are replaced by the contents of the -corresponding group. +characters, and numeric backreferences (\samp{\e 1}, \samp{\e 2}) and +named backreferences (\samp{\e g<1>}, \samp{\e g<name>}) are replaced +by the contents of the corresponding group. \end{methoddesc} \begin{methoddesc}[MatchObject]{group}{\optional{group1, \moreargs}} @@ -664,7 +669,7 @@ the string matching the the corresponding parenthesized group. If a group number is negative or larger than the number of groups defined in the pattern, an \exception{IndexError} exception is raised. If a group is contained in a part of the pattern that did not match, -the corresponding result is \code{-1}. If a group is contained in a +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 returned. |