diff options
Diffstat (limited to 'Doc/howto')
| -rw-r--r-- | Doc/howto/TODO | 4 | ||||
| -rw-r--r-- | Doc/howto/curses.tex | 55 | ||||
| -rw-r--r-- | Doc/howto/doanddont.tex | 2 | ||||
| -rw-r--r-- | Doc/howto/regex.tex | 182 |
4 files changed, 129 insertions, 114 deletions
diff --git a/Doc/howto/TODO b/Doc/howto/TODO index b858d58..c229828 100644 --- a/Doc/howto/TODO +++ b/Doc/howto/TODO @@ -1,7 +1,7 @@ Short-term tasks: - Quick revision pass to make HOWTOs match the current state of Python: -curses doanddont regex sockets sorting + Quick revision pass to make HOWTOs match the current state of Python +doanddont regex sockets Medium-term tasks: Revisit the regex howto. diff --git a/Doc/howto/curses.tex b/Doc/howto/curses.tex index 9264c0e..3e4cada 100644 --- a/Doc/howto/curses.tex +++ b/Doc/howto/curses.tex @@ -2,7 +2,7 @@ \title{Curses Programming with Python} -\release{2.01} +\release{2.02} \author{A.M. Kuchling, Eric S. Raymond} \authoraddress{\email{amk@amk.ca}, \email{esr@thyrsus.com}} @@ -147,10 +147,10 @@ makes using the shell difficult. In Python you can avoid these complications and make debugging much easier by importing the module \module{curses.wrapper}. It supplies a -function \function{wrapper} that takes a hook argument. It does the +\function{wrapper()} function that takes a callable. It does the initializations described above, and also initializes colors if color -support is present. It then runs your hook, and then finally -deinitializes appropriately. The hook is called inside a try-catch +support is present. It then runs your provided callable and finally +deinitializes appropriately. The callable is called inside a try-catch clause which catches exceptions, performs curses deinitialization, and then passes the exception upwards. Thus, your terminal won't be left in a funny state on exception. @@ -159,7 +159,7 @@ in a funny state on exception. Windows are the basic abstraction in curses. A window object represents a rectangular area of the screen, and supports various - methods to display text, erase it, allow the user to input strings, +methods to display text, erase it, allow the user to input strings, and so forth. The \code{stdscr} object returned by the \function{initscr()} function @@ -223,14 +223,14 @@ pad.refresh( 0,0, 5,5, 20,75) The \function{refresh()} call displays a section of the pad in the rectangle extending from coordinate (5,5) to coordinate (20,75) on the -screen;the upper left corner of the displayed section is coordinate +screen; the upper left corner of the displayed section is coordinate (0,0) on the pad. Beyond that difference, pads are exactly like ordinary windows and support the same methods. If you have multiple windows and pads on screen there is a more efficient way to go, which will prevent annoying screen flicker at -refresh time. Use the methods \method{noutrefresh()} and/or -\method{noutrefresh()} of each window to update the data structure +refresh time. Use the \method{noutrefresh()} method +of each window to update the data structure representing the desired state of the screen; then change the physical screen to match the desired state in one go with the function \function{doupdate()}. The normal \method{refresh()} method calls @@ -254,9 +254,9 @@ four different forms. \begin{tableii}{|c|l|}{textrm}{Form}{Description} \lineii{\var{str} or \var{ch}}{Display the string \var{str} or -character \var{ch}} +character \var{ch} at the current position} \lineii{\var{str} or \var{ch}, \var{attr}}{Display the string \var{str} or -character \var{ch}, using attribute \var{attr}} +character \var{ch}, using attribute \var{attr} at the current position} \lineii{\var{y}, \var{x}, \var{str} or \var{ch}} {Move to position \var{y,x} within the window, and display \var{str} or \var{ch}} @@ -271,7 +271,7 @@ in more detail in the next subsection. The \function{addstr()} function takes a Python string as the value to be displayed, while the \function{addch()} functions take a character, -which can be either a Python string of length 1, or an integer. If +which can be either a Python string of length 1 or an integer. If it's a string, you're limited to displaying characters between 0 and 255. SVr4 curses provides constants for extension characters; these constants are integers greater than 255. For example, @@ -331,15 +331,15 @@ The curses library also supports color on those terminals that provide it, The most common such terminal is probably the Linux console, followed by color xterms. -To use color, you must call the \function{start_color()} function -soon after calling \function{initscr()}, to initialize the default -color set (the \function{curses.wrapper.wrapper()} function does this +To use color, you must call the \function{start_color()} function soon +after calling \function{initscr()}, to initialize the default color +set (the \function{curses.wrapper.wrapper()} function does this automatically). Once that's done, the \function{has_colors()} function returns TRUE if the terminal in use can actually display -color. (Note from AMK: curses uses the American spelling -'color', instead of the Canadian/British spelling 'colour'. If you're -like me, you'll have to resign yourself to misspelling it for the sake -of these functions.) +color. (Note: curses uses the American spelling 'color', instead of +the Canadian/British spelling 'colour'. If you're used to the British +spelling, you'll have to resign yourself to misspelling it for the +sake of these functions.) The curses library maintains a finite number of color pairs, containing a foreground (or text) color and a background color. You @@ -400,18 +400,19 @@ Python's support adds a text-input widget that makes up some of the lack. The most common way to get input to a window is to use its -\method{getch()} method. that pauses, and waits for the user to hit -a key, displaying it if \function{echo()} has been called earlier. -You can optionally specify a coordinate to which the cursor should be -moved before pausing. +\method{getch()} method. \method{getch()} pauses and waits for the +user to hit a key, displaying it if \function{echo()} has been called +earlier. You can optionally specify a coordinate to which the cursor +should be moved before pausing. It's possible to change this behavior with the method \method{nodelay()}. After \method{nodelay(1)}, \method{getch()} for -the window becomes non-blocking and returns ERR (-1) when no input is -ready. There's also a \function{halfdelay()} function, which can be -used to (in effect) set a timer on each \method{getch()}; if no input -becomes available within the number of milliseconds specified as the -argument to \function{halfdelay()}, curses throws an exception. +the window becomes non-blocking and returns \code{curses.ERR} (a value +of -1) when no input is ready. There's also a \function{halfdelay()} +function, which can be used to (in effect) set a timer on each +\method{getch()}; if no input becomes available within the number of +milliseconds specified as the argument to \function{halfdelay()}, +curses raises an exception. The \method{getch()} method returns an integer; if it's between 0 and 255, it represents the ASCII code of the key pressed. Values greater diff --git a/Doc/howto/doanddont.tex b/Doc/howto/doanddont.tex index d81c374..0cd5d91 100644 --- a/Doc/howto/doanddont.tex +++ b/Doc/howto/doanddont.tex @@ -32,7 +32,7 @@ plain dangerous. \subsubsection{Inside Function Definitions} \code{from module import *} is {\em invalid} inside function definitions. -While many versions of Python do no check for the invalidity, it does not +While many versions of Python do not check for the invalidity, it does not make it more valid, no more then having a smart lawyer makes a man innocent. Do not use it like that ever. Even in versions where it was accepted, it made the function execution slower, because the compiler could not be certain diff --git a/Doc/howto/regex.tex b/Doc/howto/regex.tex index 3c63b3a..62b6daf 100644 --- a/Doc/howto/regex.tex +++ b/Doc/howto/regex.tex @@ -34,17 +34,18 @@ This document is available from The \module{re} module was added in Python 1.5, and provides Perl-style regular expression patterns. Earlier versions of Python came with the \module{regex} module, which provided Emacs-style -patterns. \module{regex} module was removed in Python 2.5. - -Regular expressions (or REs) are essentially a tiny, highly -specialized programming language embedded inside Python and made -available through the \module{re} module. Using this little language, -you specify the rules for the set of possible strings that you want to -match; this set might contain English sentences, or e-mail addresses, -or TeX commands, or anything you like. You can then ask questions -such as ``Does this string match the pattern?'', or ``Is there a match -for the pattern anywhere in this string?''. You can also use REs to -modify a string or to split it apart in various ways. +patterns. The \module{regex} module was removed completely in Python 2.5. + +Regular expressions (called REs, or regexes, or regex patterns) are +essentially a tiny, highly specialized programming language embedded +inside Python and made available through the \module{re} module. +Using this little language, you specify the rules for the set of +possible strings that you want to match; this set might contain +English sentences, or e-mail addresses, or TeX commands, or anything +you like. You can then ask questions such as ``Does this string match +the pattern?'', or ``Is there a match for the pattern anywhere in this +string?''. You can also use REs to modify a string or to split it +apart in various ways. Regular expression patterns are compiled into a series of bytecodes which are then executed by a matching engine written in C. For @@ -80,11 +81,12 @@ example, the regular expression \regexp{test} will match the string would let this RE match \samp{Test} or \samp{TEST} as well; more about this later.) -There are exceptions to this rule; some characters are -special, and don't match themselves. Instead, they signal that some -out-of-the-ordinary thing should be matched, or they affect other -portions of the RE by repeating them. Much of this document is -devoted to discussing various metacharacters and what they do. +There are exceptions to this rule; some characters are special +\dfn{metacharacters}, and don't match themselves. Instead, they +signal that some out-of-the-ordinary thing should be matched, or they +affect other portions of the RE by repeating them or changing their +meaning. Much of this document is devoted to discussing various +metacharacters and what they do. Here's a complete list of the metacharacters; their meanings will be discussed in the rest of this HOWTO. @@ -111,9 +113,10 @@ Metacharacters are not active inside classes. For example, usually a metacharacter, but inside a character class it's stripped of its special nature. -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 class; \character{\^} elsewhere will simply match the +You can match the characters not listed within the class by +\dfn{complementing} the set. This is indicated by including a +\character{\^} as the first character of the class; \character{\^} +outside a character class will simply match the \character{\^} character. For example, \verb|[^5]| will match any character except \character{5}. @@ -176,7 +179,7 @@ or more times, instead of exactly once. For example, \regexp{ca*t} will match \samp{ct} (0 \samp{a} characters), \samp{cat} (1 \samp{a}), \samp{caaat} (3 \samp{a} characters), and so forth. The RE engine has various internal -limitations stemming from the size of C's \code{int} type, that will +limitations stemming from the size of C's \code{int} type that will prevent it from matching over 2 billion \samp{a} characters; you probably don't have enough memory to construct a string that large, so you shouldn't run into that limit. @@ -238,9 +241,9 @@ will match \samp{a/b}, \samp{a//b}, and \samp{a///b}. It won't match You can omit either \var{m} or \var{n}; in that case, a reasonable value is assumed for the missing value. Omitting \var{m} is -interpreted as a lower limit of 0, while omitting \var{n} results in an -upper bound of infinity --- actually, the 2 billion limit mentioned -earlier, but that might as well be infinity. +interpreted as a lower limit of 0, while omitting \var{n} results in +an upper bound of infinity --- actually, the upper bound is the +2-billion limit mentioned earlier, but that might as well be infinity. Readers of a reductionist bent may notice that the three other qualifiers can all be expressed using this notation. \regexp{\{0,\}} is the same @@ -285,7 +288,7 @@ them. (There are applications that don't need REs at all, so there's no need to bloat the language specification by including them.) Instead, the \module{re} module is simply a C extension module included with Python, just like the \module{socket} or \module{zlib} -module. +modules. Putting REs in strings keeps the Python language simpler, but has one disadvantage which is the topic of the next section. @@ -326,7 +329,7 @@ expressions; backslashes are not handled in any special way in a string literal prefixed with \character{r}, so \code{r"\e n"} is a two-character string containing \character{\e} and \character{n}, while \code{"\e n"} is a one-character string containing a newline. -Frequently regular expressions will be expressed in Python +Regular expressions will often be written in Python code using this raw string notation. \begin{tableii}{c|c}{code}{Regular String}{Raw string} @@ -368,9 +371,9 @@ strings, and displays whether the RE matches or fails. \file{redemo.py} can be quite useful when trying to debug a complicated RE. Phil Schwartz's \ulink{Kodos}{http://www.phil-schwartz.com/kodos.spy} is also an interactive -tool for developing and testing RE patterns. This HOWTO will use the -standard Python interpreter for its examples. +tool for developing and testing RE patterns. +This HOWTO uses the standard Python interpreter for its examples. First, run the Python interpreter, import the \module{re} module, and compile a RE: @@ -401,7 +404,7 @@ Now, let's try it on a string that it should match, such as later use. \begin{verbatim} ->>> m = p.match( 'tempo') +>>> m = p.match('tempo') >>> print m <_sre.SRE_Match object at 80c4f68> \end{verbatim} @@ -472,9 +475,9 @@ Two \class{RegexObject} methods return all of the matches for a pattern. \end{verbatim} \method{findall()} has to create the entire list before it can be -returned as the result. In Python 2.2, the \method{finditer()} method -is also available, returning a sequence of \class{MatchObject} instances -as an iterator. +returned as the result. The \method{finditer()} method returns a +sequence of \class{MatchObject} instances as an +iterator.\footnote{Introduced in Python 2.2.2.} \begin{verbatim} >>> iterator = p.finditer('12 drummers drumming, 11 ... 10 ...') @@ -491,13 +494,13 @@ as an iterator. \subsection{Module-Level Functions} -You don't have to produce a \class{RegexObject} and call its methods; +You don't have to create a \class{RegexObject} and call its methods; the \module{re} module also provides top-level functions called -\function{match()}, \function{search()}, \function{sub()}, and so -forth. These functions take the same arguments as the corresponding -\class{RegexObject} method, with the RE string added as the first -argument, and still return either \code{None} or a \class{MatchObject} -instance. +\function{match()}, \function{search()}, \function{findall()}, +\function{sub()}, and so forth. These functions take the same +arguments as the corresponding \class{RegexObject} method, with the RE +string added as the first argument, and still return either +\code{None} or a \class{MatchObject} instance. \begin{verbatim} >>> print re.match(r'From\s+', 'Fromage amk') @@ -514,7 +517,7 @@ RE are faster. Should you use these module-level functions, or should you get the \class{RegexObject} and call its methods yourself? That choice depends on how frequently the RE will be used, and on your personal -coding style. If a RE is being used at only one point in the code, +coding style. If the RE is being used at only one point in the code, then the module functions are probably more convenient. If a program contains a lot of regular expressions, or re-uses the same ones in several locations, then it might be worthwhile to collect all the @@ -537,7 +540,7 @@ as I am. Compilation flags let you modify some aspects of how regular expressions work. Flags are available in the \module{re} module under -two names, a long name such as \constant{IGNORECASE}, and a short, +two names, a long name such as \constant{IGNORECASE} and a short, one-letter form such as \constant{I}. (If you're familiar with Perl's pattern modifiers, the one-letter forms use the same letters; the short form of \constant{re.VERBOSE} is \constant{re.X}, for example.) @@ -617,7 +620,7 @@ that are more readable by granting you more flexibility in how you can format them. When this flag has been specified, whitespace within the RE string is ignored, except when the whitespace is in a character class or preceded by an unescaped backslash; this lets you organize -and indent the RE more clearly. It also enables you to put comments +and indent the RE more clearly. This flag also lets you put comments within a RE that will be ignored by the engine; comments are marked by a \character{\#} that's neither in a character class or preceded by an unescaped backslash. @@ -629,18 +632,19 @@ much easier it is to read? charref = re.compile(r""" &[#] # Start of a numeric entity reference ( - [0-9]+[^0-9] # Decimal form - | 0[0-7]+[^0-7] # Octal form - | x[0-9a-fA-F]+[^0-9a-fA-F] # Hexadecimal form + 0[0-7]+ # Octal form + | [0-9]+ # Decimal form + | x[0-9a-fA-F]+ # Hexadecimal form ) + ; # Trailing semicolon """, re.VERBOSE) \end{verbatim} Without the verbose setting, the RE would look like this: \begin{verbatim} -charref = re.compile("&#([0-9]+[^0-9]" - "|0[0-7]+[^0-7]" - "|x[0-9a-fA-F]+[^0-9a-fA-F])") +charref = re.compile("&#(0[0-7]+" + "|[0-9]+" + "|x[0-9a-fA-F]+);") \end{verbatim} In the above example, Python's automatic concatenation of string @@ -722,12 +726,12 @@ inside a character class, as in \regexp{[\$]}. \item[\regexp{\e A}] Matches only at the start of the string. When not in \constant{MULTILINE} mode, \regexp{\e A} and \regexp{\^} are -effectively the same. In \constant{MULTILINE} mode, however, they're -different; \regexp{\e A} still matches only at the beginning of the +effectively the same. In \constant{MULTILINE} mode, they're +different: \regexp{\e A} still matches only at the beginning of the string, but \regexp{\^} may match at any location inside the string that follows a newline character. -\item[\regexp{\e Z}]Matches only at the end of the string. +\item[\regexp{\e Z}] Matches only at the end of the string. \item[\regexp{\e b}] Word boundary. This is a zero-width assertion that matches only at the @@ -782,14 +786,23 @@ RE matched or not. Regular expressions are often used to dissect strings by writing a RE divided into several subgroups which match different components of interest. For example, an RFC-822 header line is divided into a header name and a value, separated by a -\character{:}. This can be handled by writing a regular expression +\character{:}, like this: + +\begin{verbatim} +From: author@example.com +User-Agent: Thunderbird 1.5.0.9 (X11/20061227) +MIME-Version: 1.0 +To: editor@example.com +\end{verbatim} + +This can be handled by writing a regular expression which matches an entire header line, and has one group which matches the header name, and another group which matches the header's value. Groups are marked by the \character{(}, \character{)} metacharacters. \character{(} and \character{)} have much the same meaning as they do in mathematical expressions; they group together the expressions -contained inside them. For example, you can repeat the contents of a +contained inside them, and you can repeat the contents of a group with a repeating qualifier, such as \regexp{*}, \regexp{+}, \regexp{?}, or \regexp{\{\var{m},\var{n}\}}. For example, \regexp{(ab)*} will match zero or more repetitions of \samp{ab}. @@ -881,12 +894,13 @@ two features which help with this problem. Both of them use a common syntax for regular expression extensions, so we'll look at that first. Perl 5 added several additional features to standard regular -expressions, and the Python \module{re} module supports most of them. -It would have been difficult to choose new single-keystroke -metacharacters or new special sequences beginning with \samp{\e} to -represent the new features without making Perl's regular expressions -confusingly different from standard REs. If you chose \samp{\&} as a -new metacharacter, for example, old expressions would be assuming that +expressions, and the Python \module{re} module supports most of them. +It would have been difficult to choose new +single-keystroke metacharacters or new special sequences beginning +with \samp{\e} to represent the new features without making Perl's +regular expressions confusingly different from standard REs. If you +chose \samp{\&} as a new metacharacter, for example, old expressions +would be assuming that \samp{\&} was a regular character and wouldn't have escaped it by writing \regexp{\e \&} or \regexp{[\&]}. @@ -913,15 +927,15 @@ Now that we've looked at the general extension syntax, we can return to the features that simplify working with groups in complex REs. Since groups are numbered from left to right and a complex expression may use many groups, it can become difficult to keep track of the -correct numbering, and modifying such a complex RE is annoying. -Insert a new group near the beginning, and you change the numbers of +correct numbering. Modifying such a complex RE is annoying, too: +insert a new group near the beginning and you change the numbers of everything that follows it. -First, sometimes you'll want to use a group to collect a part of a -regular expression, but aren't interested in retrieving the group's -contents. You can make this fact explicit by using a non-capturing -group: \regexp{(?:...)}, where you can put any other regular -expression inside the parentheses. +Sometimes you'll want to use a group to collect a part of a regular +expression, but aren't interested in retrieving the group's contents. +You can make this fact explicit by using a non-capturing group: +\regexp{(?:...)}, where you can replace the \regexp{...} +with any other regular expression. \begin{verbatim} >>> m = re.match("([abc])+", "abc") @@ -937,23 +951,23 @@ group matched, a non-capturing group behaves exactly the same as a capturing group; you can put anything inside it, repeat it with a repetition metacharacter such as \samp{*}, and nest it within other groups (capturing or non-capturing). \regexp{(?:...)} is particularly -useful when modifying an existing group, since you can add new groups +useful when modifying an existing pattern, since you can add new groups without changing how all the other groups are numbered. It should be mentioned that there's no performance difference in searching between capturing and non-capturing groups; neither form is any faster than the other. -The second, and more significant, feature is named groups; instead of +A more significant feature is named groups: instead of referring to them by numbers, groups can be referenced by a name. The syntax for a named group is one of the Python-specific extensions: \regexp{(?P<\var{name}>...)}. \var{name} is, obviously, the name of -the group. Except for associating a name with a group, named groups -also behave identically to capturing groups. The \class{MatchObject} -methods that deal with capturing groups all accept either integers, to -refer to groups by number, or a string containing the group name. -Named groups are still given numbers, so you can retrieve information -about a group in two ways: +the group. Named groups also behave exactly like capturing groups, +and additionally associate a name with a group. The +\class{MatchObject} methods that deal with capturing groups all accept +either integers that refer to the group by number or strings that +contain the desired group's name. Named groups are still given +numbers, so you can retrieve information about a group in two ways: \begin{verbatim} >>> p = re.compile(r'(?P<word>\b\w+\b)') @@ -980,11 +994,11 @@ InternalDate = re.compile(r'INTERNALDATE "' It's obviously much easier to retrieve \code{m.group('zonem')}, instead of having to remember to retrieve group 9. -Since the syntax for backreferences, in an expression like -\regexp{(...)\e 1}, refers to the number of the group there's +The syntax for backreferences in an expression such as +\regexp{(...)\e 1} refers to the number of the group. There's naturally a variant that uses the group name instead of the number. -This is also a Python extension: \regexp{(?P=\var{name})} indicates -that the contents of the group called \var{name} should again be found +This is another Python extension: \regexp{(?P=\var{name})} indicates +that the contents of the group called \var{name} should again be matched at the current point. The regular expression for finding doubled words, \regexp{(\e b\e w+)\e s+\e 1} can also be written as \regexp{(?P<word>\e b\e w+)\e s+(?P=word)}: @@ -1014,11 +1028,11 @@ opposite of the positive assertion; it succeeds if the contained expression \emph{doesn't} match at the current position in the string. \end{itemize} -An example will help make this concrete by demonstrating a case -where a lookahead is useful. Consider a simple pattern to match a -filename and split it apart into a base name and an extension, -separated by a \samp{.}. For example, in \samp{news.rc}, \samp{news} -is the base name, and \samp{rc} is the filename's extension. +To make this concrete, let's look at a case where a lookahead is +useful. Consider a simple pattern to match a filename and split it +apart into a base name and an extension, separated by a \samp{.}. For +example, in \samp{news.rc}, \samp{news} is the base name, and +\samp{rc} is the filename's extension. The pattern to match this is quite simple: @@ -1065,12 +1079,12 @@ read and understand. Worse, if the problem changes and you want to exclude both \samp{bat} and \samp{exe} as extensions, the pattern would get even more complicated and confusing. -A negative lookahead cuts through all this: +A negative lookahead cuts through all this confusion: \regexp{.*[.](?!bat\$).*\$} % $ -The lookahead means: if the expression \regexp{bat} doesn't match at +The negative lookahead means: if the expression \regexp{bat} doesn't match at this point, try the rest of the pattern; if \regexp{bat\$} does match, the whole pattern will fail. The trailing \regexp{\$} is required to ensure that something like \samp{sample.batch}, where the extension @@ -1087,7 +1101,7 @@ filenames that end in either \samp{bat} or \samp{exe}: \section{Modifying Strings} Up to this point, we've simply performed searches against a static -string. Regular expressions are also commonly used to modify a string +string. Regular expressions are also commonly used to modify strings in various ways, using the following \class{RegexObject} methods: \begin{tableii}{c|l}{code}{Method/Attribute}{Purpose} |