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<H1><A NAME="SECTION0021300000000000000000">
19.3 Python Abstract Syntax</A>
</H1>

<P>
The <tt class="module">compiler.ast</tt> module defines an abstract syntax for
Python.  In the abstract syntax tree, each node represents a syntactic
construct.  The root of the tree is <tt class="class">Module</tt> object.

<P>
The abstract syntax offers a higher level interface to parsed Python
source code.  The <a class="ulink" href="http://www.python.org/doc/current/lib/module-parser.html"
  ><tt class="module">parser</tt></a>
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.

<P>
The abstract syntax tree is created by the
<tt class="module">compiler.transformer</tt> 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.  

<P>
The <tt class="module">transformer</tt> module was created by Greg
Stein<a id='l2h-5025' xml:id='l2h-5025'></a> and Bill Tutt<a id='l2h-5026' xml:id='l2h-5026'></a> for an
experimental 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.

<P>

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	54
	55	<H1><A NAME="SECTION0021300000000000000000">
	56	19.3 Python Abstract Syntax</A>
	57	</H1>
	58
	59	<P>
	60	The <tt class="module">compiler.ast</tt> module defines an abstract syntax for
	61	Python. In the abstract syntax tree, each node represents a syntactic
	62	construct. The root of the tree is <tt class="class">Module</tt> object.
	63
	64	<P>
65	The abstract syntax offers a higher level interface to parsed Python
66	source code. The <a class="ulink" href="http://www.python.org/doc/current/lib/module-parser.html"
67	><tt class="module">parser</tt></a>
68	module and the compiler written in C for the Python interpreter use a
69	concrete syntax tree. The concrete syntax is tied closely to the
70	grammar description used for the Python parser. Instead of a single
71	node for a construct, there are often several levels of nested nodes
72	that are introduced by Python's precedence rules.
73
74	<P>
75	The abstract syntax tree is created by the
76	<tt class="module">compiler.transformer</tt> module. The transformer relies on the
77	builtin Python parser to generate a concrete syntax tree. It
78	generates an abstract syntax tree from the concrete tree.
79
80	<P>
81	The <tt class="module">transformer</tt> module was created by Greg
82	Stein<a id='l2h-5025' xml:id='l2h-5025'></a> and Bill Tutt<a id='l2h-5026' xml:id='l2h-5026'></a> for an
83	experimental Python-to-C compiler. The current version contains a
84	number of modifications and improvements, but the basic form of the
85	abstract syntax and of the transformer are due to Stein and Tutt.
86
87	<P>
88
89	<p><br /></p><hr class='online-navigation' />
90	<div class='online-navigation'>
91	<!--Table of Child-Links-->
92	<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
93
94	<UL CLASS="ChildLinks">
95	<LI><A href="module-compiler.ast.html">19.3.1 AST Nodes</a>
96	<LI><A href="node794.html">19.3.2 Assignment nodes</a>
97	<LI><A href="node795.html">19.3.3 Examples</a>
98	</ul>
99	<!--End of Table of Child-Links-->
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