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diff --git a/Tools/compiler/doc/compiler.tex b/Tools/compiler/doc/compiler.tex new file mode 100644 index 0000000..98ac5f2 --- /dev/null +++ b/Tools/compiler/doc/compiler.tex @@ -0,0 +1,305 @@ +% Complete documentation on the extended LaTeX markup used for Python +% documentation is available in ``Documenting Python'', which is part +% of the standard documentation for Python. It may be found online +% at: +% +% http://www.python.org/doc/current/doc/doc.html + +\documentclass{manual} + +\title{Python compiler package} + +\author{Jeremy Hylton} + +% Please at least include a long-lived email address; +% the rest is at your discretion. +\authoraddress{ + PythonLabs \\ + Zope Corp. \\ + Email: \email{jeremy@zope.com} +} + +\date{August 15, 2001} % update before release! + % Use an explicit date so that reformatting + % doesn't cause a new date to be used. Setting + % the date to \today can be used during draft + % stages to make it easier to handle versions. + +\release{2.2} % release version; this is used to define the + % \version macro + +\makeindex % tell \index to actually write the .idx file +\makemodindex % If this contains a lot of module sections. + + +\begin{document} + +\maketitle + +% This makes the contents more accessible from the front page of the HTML. +\ifhtml +\chapter*{Front Matter\label{front}} +\fi + +%\input{copyright} + +\begin{abstract} + +\noindent +The Python compiler package is a tool for analyzing Python source code +and generating Python bytecode. The compiler contains libraries to +generate an abstract syntax tree from Python source code and to +generate Python bytecode from the tree. + +\end{abstract} + +\tableofcontents + +\chapter{Introduction\label{Introduction}} + +XXX Need basic intro + +XXX what are the major advantages... the abstract syntax is much +closer to the python source... + +\section{The basic interface} + +The top-level of the package defines four functions. + +\begin{funcdesc}{parse}{buf} +Returns an abstract syntax tree for the Python source code in \var{buf}. +The function raises SyntaxError if there is an error in the source +code. The return value is a \class{compiler.ast.Module} instance that +contains the tree. +\end{funcdesc} + +\begin{funcdesc}{parseFile}{path} +Return an abstract syntax tree for the Python source code in the file +specified by \var{path}. It is equivalent to \code{parse(open(path))}. +\end{funcdesc} + +\begin{funcdesc}{walk}{ast, visitor, \optional{verbose=None}} +Do a pre-order walk over the abstract syntax tree \var{ast}. Call the +appropriate method on the \var{visitor} instance for each node +encountered. +\end{funcdesc} + +\begin{funcdesc}{compile}{filename} +Compile the file \var{filename} and generated \var{filename}.pyc. +\end{funcdesc} + +The \module{compiler} package contains the following modules: +\module{ast}, \module{consts}, \module{future}, \module{misc}, +\module{pyassem}, \module{pycodegen}, \module{symbols}, +\module{transformer}, and \module{visitor}. + +\section{Limitations} + +There are some problems with the error checking of the compiler +package. The interpreter detects syntax errors in two distinct +phases. One set of errors is detected by the interpreter's parser, +the other set by the compiler. The compiler package relies on the +interpreter's parser, so it get the first phases of error checking for +free. It implements the second phase itself, and that implement is +incomplete. For example, the compiler package does not raise an error +if a name appears more than once in an argument list: +\code{def f(x, x): ...} + +\chapter{Python Abstract Syntax} + +\section{Introduction} + +The \module{compiler.ast} module defines an abstract syntax for +Python. In the abstract syntax tree, each node represents a syntactic +construct. The root of the tree is \class{Module} object. + +The abstract syntax offers a higher level interface to parsed Python +source code. The \module{parser} module and the compiler written in C +for the Python interpreter use a concrete syntax tree. The concrete +syntax is tied closely to the grammar description used for the Python +parser. Instead of a single node for a construct, there are often +several levels of nested nodes that are introduced by Python's +precedence rules. + +The abstract syntax tree is created by the +\module{compiler.transformer} module. The transformer relies on the +builtin Python parser to generate a concrete syntax tree. It +generates an abstract syntax tree from the concrete tree. + +The \module{transformer} module was created by Greg Stein and Bill +Tutt for the Python-to-C compiler. The current version contains a +number of modifications and improvements, but the basic form of the +abstract syntax and of the transformer are due to Stein and Tutt. + +\section{AST Nodes} + +The \module{ast} module is generated from a text file that describes +each node type and its elements. Each node type is represented as a +class that inherits from the abstract base class \class{ast.Node} and +defines a set of named attributes for child nodes. + +\begin{classdesc}{Node}{} + + The \class{Node} instances are created automatically by the parser + generator. The recommended interface for specific \class{Node} + instances is to use the public attributes to access child nodes. A + public attribute may be bound to a single node or to a sequence of + nodes, depending on the \class{Node} type. For example, the + \member{bases} attribute of the \class{Class} node, is bound to a + list of base class nodes, and the \member{doc} attribute is bound to + a single node. + + Each \class{Node} instance has a \member{lineno} attribute which may + be \code{None}. XXX Not sure what the rules are for which nodes + will have a useful lineno. + + \begin{methoddesc}{getChildren}{} + Returns a flattened list of the child nodes and objects in the + order they occur. Specifically, the order of the nodes is the + order in which they appear in the Python grammar. Not all of the + children are \class{Node} instances. The names of functions and + classes, for example, are plain strings. + \end{methoddesc} + + \begin{methoddesc}{getChildNodes}{} + Returns a flattened list of the child nodes in the order they + occur. This method is like \method{getChildNodes}, except that it + only returns those children that are \class{Node} instances. + \end{methoddesc} + +\end{classdesc} + +Two examples illustrate the general structure of \class{Node} +classes. The while statement is defined by the following grammar +production: + +\begin{verbatim} +while_stmt: "while" expression ":" suite + ["else" ":" suite] +\end{verbatim} + +The \class{While} node has three attributes: \member{test}, +\member{body}, and \member{else_}. (If the natural name for an +attribute is also a Python reserved word, it can't be used as an +attribute name. An underscore is appended to the word to make it +legal, hence \code{else_} instead of \code{else}.) + +The if statement is more complicated because it can include several +tests. + +\begin{verbatim} +if_stmt: 'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite] +\end{verbatim} + +The \class{If} node only defines two attributes: \member{tests} and +\member{else_}. The \member{tests} attribute is a sequence of test +expression, consequent body pairs. There is one pair of each if/elif +clause. The first element of the pair is the test expression. The +second elements is a \class{Stmt} node that contains the code to +execute if the test is true. + +The \method{getChildren()} method of \class{If} returns a flat list of +child nodes. If there are three if/elif clauses and no else clause, +then \method{getChildren()} will return a list of six elements: the +first test expression, the first \class{Stmt}, the second text +expression, etc. + +The following table lists each of the \class{Node} subclasses defined +in \module{compiler.ast} and each of the public attributes available +on their instances. The values of most of the attributes are +themselves \class{Node} instances or sequences of instances. When the +value is something other than an instance, the type is noted in the +comment. The attributes are listed in the order in which they are +returned by \method{getChildren} and \method{getChildNodes}. + +\input{asttable} + +\section{Assignment nodes} + +There is a collection of nodes used to represent assignments. Each +assignment statement in the source code becomes a single +\class{Assign} node in the AST. The \member{nodes} attribute is a +list that contains a node for each assignment target. This is +necessary because assignment can be chained, e.g. \code{a = b = 2}. +Each \class{Node} in the list will be one of the following classes: +\class{AssAttr}, \class{AssList}, \class{AssName}, or +\class{AssTuple}. + +XXX Explain what the AssXXX nodes are for. Mention \code{a.b.c = 2} +as an example. Explain what the flags are for. + +\chapter{Using Visitors to Walk ASTs} + +The visitor pattern is ... The \module{compiler} package uses a +variant on the visitor pattern that takes advantage of Python's +introspection features to elminiate the need for much of the visitor's +infrastructure. + +The classes being visited do not need to be programmed to accept +visitors. The visitor need only define visit methods for classes it +is specifically interested in; a default visit method can handle the +rest. + +XXX The magic \method{visit()} method for visitors. + +\begin{classdesc}{ASTVisitor}{} + +The \class{ASTVisitor} is responsible for walking over the tree in the +correct order. A walk begins with a call to \method{preorder()}. For +each node, it checks the \var{visitor} argument to \method{preorder{}} +for a method named `visitNodeType,' where NodeType is the name of the +node's class, e.g. for a \class{While} node a \method{visitWhile} +would be called . If the method exists, it is called with the node as +its first argument. + +The visitor method for a particular node type can control how child +nodes are visited during the walk. The \class{ASTVisitor} modifies +the visitor argument by adding a visit method to the visitor; this +method can be used to visit a particular child node. If no visitor is +found for a particular node type, the \method{default} method is +called. + +XXX describe extra arguments + +\begin{methoddesc}{default}{node\optional{, *args}} +\end{methoddesc} + +\begin{methoddesc}{dispatch}{node\optional{, *args}} +\end{methoddesc} + +\begin{methoddesc}{preorder}{tree, visitor} +\end{methoddesc} + +\end{classdesc} + +\begin{funcdesc}{walk}{tree, visitor\optional{, verbose=None}} +\end{funcdesc} + +\chapter{Bytecode Generation} + +The code generator is a visit that emits bytecodes. Each visit method +can call the \method{emit} method to emit a new bytecode. The basic +code generator is specialized for modules, classes, and functions. An +assembler converts that emitted instructions to the low-level bytecode +format. It handles things like generator of constant lists of code +objects and calculation of jump offsets. + +% +% The ugly "%begin{latexonly}" pseudo-environments are really just to +% keep LaTeX2HTML quiet during the \renewcommand{} macros; they're +% not really valuable. +% +% If you don't want the Module Index, you can remove all of this up +% until the second \input line. +% +%begin{latexonly} +\renewcommand{\indexname}{Module Index} +%end{latexonly} +\input{mod\jobname.ind} % Module Index + +%begin{latexonly} +\renewcommand{\indexname}{Index} +%end{latexonly} +\input{\jobname.ind} % Index + +\end{document} |