projects / OpenSPARC-T2-SAM / blame
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| 55 | <H2><A NAME="SECTION0020120000000000000000"></A><A NAME="Converting_ASTs"></A> | |
| 56 | <BR> | |
| 57 | 18.1.2 Converting AST Objects | |
| 58 | </H2> | |
| 59 | ||
| 60 | <P> | |
| 61 | AST objects, regardless of the input used to create them, may be | |
| 62 | converted to parse trees represented as list- or tuple- trees, or may | |
| 63 | be compiled into executable code objects. Parse trees may be | |
| 64 | extracted with or without line numbering information. | |
| 65 | ||
| 66 | <P> | |
| 67 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 68 | <td><nobr><b><tt id='l2h-4942' xml:id='l2h-4942' class="function">ast2list</tt></b>(</nobr></td> | |
| 69 | <td><var>ast</var><big>[</big><var>, line_info</var><big>]</big><var></var>)</td></tr></table></dt> | |
| 70 | <dd> | |
| 71 | This function accepts an AST object from the caller in | |
| 72 | <var>ast</var> and returns a Python list representing the | |
| 73 | equivalent parse tree. The resulting list representation can be used | |
| 74 | for inspection or the creation of a new parse tree in list form. This | |
| 75 | function does not fail so long as memory is available to build the | |
| 76 | list representation. If the parse tree will only be used for | |
| 77 | inspection, <tt class="function">ast2tuple()</tt> should be used instead to reduce memory | |
| 78 | consumption and fragmentation. When the list representation is | |
| 79 | required, this function is significantly faster than retrieving a | |
| 80 | tuple representation and converting that to nested lists. | |
| 81 | ||
| 82 | <P> | |
| 83 | If <var>line_info</var> is true, line number information will be | |
| 84 | included for all terminal tokens as a third element of the list | |
| 85 | representing the token. Note that the line number provided specifies | |
| 86 | the line on which the token <em>ends</em>. This information is | |
| 87 | omitted if the flag is false or omitted. | |
| 88 | </dl> | |
| 89 | ||
| 90 | <P> | |
| 91 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 92 | <td><nobr><b><tt id='l2h-4943' xml:id='l2h-4943' class="function">ast2tuple</tt></b>(</nobr></td> | |
| 93 | <td><var>ast</var><big>[</big><var>, line_info</var><big>]</big><var></var>)</td></tr></table></dt> | |
| 94 | <dd> | |
| 95 | This function accepts an AST object from the caller in | |
| 96 | <var>ast</var> and returns a Python tuple representing the | |
| 97 | equivalent parse tree. Other than returning a tuple instead of a | |
| 98 | list, this function is identical to <tt class="function">ast2list()</tt>. | |
| 99 | ||
| 100 | <P> | |
| 101 | If <var>line_info</var> is true, line number information will be | |
| 102 | included for all terminal tokens as a third element of the list | |
| 103 | representing the token. This information is omitted if the flag is | |
| 104 | false or omitted. | |
| 105 | </dl> | |
| 106 | ||
| 107 | <P> | |
| 108 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 109 | <td><nobr><b><tt id='l2h-4944' xml:id='l2h-4944' class="function">compileast</tt></b>(</nobr></td> | |
| 110 | <td><var>ast</var><big>[</big><var>, filename<code> = '<ast>'</code></var><big>]</big><var></var>)</td></tr></table></dt> | |
| 111 | <dd> | |
| 112 | The Python byte compiler can be invoked on an AST object to produce | |
| 113 | code objects which can be used as part of an <tt class="keyword">exec</tt> statement or | |
| 114 | a call to the built-in <tt class="function">eval()</tt><a id='l2h-4945' xml:id='l2h-4945'></a> function. | |
| 115 | This function provides the interface to the compiler, passing the | |
| 116 | internal parse tree from <var>ast</var> to the parser, using the | |
| 117 | source file name specified by the <var>filename</var> parameter. | |
| 118 | The default value supplied for <var>filename</var> indicates that | |
| 119 | the source was an AST object. | |
| 120 | ||
| 121 | <P> | |
| 122 | Compiling an AST object may result in exceptions related to | |
| 123 | compilation; an example would be a <tt class="exception">SyntaxError</tt> caused by the | |
| 124 | parse tree for <code>del f(0)</code>: this statement is considered legal | |
| 125 | within the formal grammar for Python but is not a legal language | |
| 126 | construct. The <tt class="exception">SyntaxError</tt> raised for this condition is | |
| 127 | actually generated by the Python byte-compiler normally, which is why | |
| 128 | it can be raised at this point by the <tt class="module">parser</tt> module. Most | |
| 129 | causes of compilation failure can be diagnosed programmatically by | |
| 130 | inspection of the parse tree. | |
| 131 | </dl> | |
| 132 | ||
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| 169 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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