projects / OpenSPARC-T2-SAM / blame
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| 54 | ||
| 55 | <H2><A NAME="SECTION0020110000000000000000"></A><A NAME="Creating_ASTs"></A> | |
| 56 | <BR> | |
| 57 | 18.1.1 Creating AST Objects | |
| 58 | </H2> | |
| 59 | ||
| 60 | <P> | |
| 61 | AST objects may be created from source code or from a parse tree. | |
| 62 | When creating an AST object from source, different functions are used | |
| 63 | to create the <code>'eval'</code> and <code>'exec'</code> forms. | |
| 64 | ||
| 65 | <P> | |
| 66 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 67 | <td><nobr><b><tt id='l2h-4938' xml:id='l2h-4938' class="function">expr</tt></b>(</nobr></td> | |
| 68 | <td><var>source</var>)</td></tr></table></dt> | |
| 69 | <dd> | |
| 70 | The <tt class="function">expr()</tt> function parses the parameter <var>source</var> | |
| 71 | as if it were an input to "<tt class="samp">compile(<var>source</var>, 'file.py', | |
| 72 | 'eval')</tt>". If the parse succeeds, an AST object is created to hold the | |
| 73 | internal parse tree representation, otherwise an appropriate exception | |
| 74 | is thrown. | |
| 75 | </dl> | |
| 76 | ||
| 77 | <P> | |
| 78 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 79 | <td><nobr><b><tt id='l2h-4939' xml:id='l2h-4939' class="function">suite</tt></b>(</nobr></td> | |
| 80 | <td><var>source</var>)</td></tr></table></dt> | |
| 81 | <dd> | |
| 82 | The <tt class="function">suite()</tt> function parses the parameter <var>source</var> | |
| 83 | as if it were an input to "<tt class="samp">compile(<var>source</var>, 'file.py', | |
| 84 | 'exec')</tt>". If the parse succeeds, an AST object is created to hold the | |
| 85 | internal parse tree representation, otherwise an appropriate exception | |
| 86 | is thrown. | |
| 87 | </dl> | |
| 88 | ||
| 89 | <P> | |
| 90 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 91 | <td><nobr><b><tt id='l2h-4940' xml:id='l2h-4940' class="function">sequence2ast</tt></b>(</nobr></td> | |
| 92 | <td><var>sequence</var>)</td></tr></table></dt> | |
| 93 | <dd> | |
| 94 | This function accepts a parse tree represented as a sequence and | |
| 95 | builds an internal representation if possible. If it can validate | |
| 96 | that the tree conforms to the Python grammar and all nodes are valid | |
| 97 | node types in the host version of Python, an AST object is created | |
| 98 | from the internal representation and returned to the called. If there | |
| 99 | is a problem creating the internal representation, or if the tree | |
| 100 | cannot be validated, a <tt class="exception">ParserError</tt> exception is thrown. An AST | |
| 101 | object created this way should not be assumed to compile correctly; | |
| 102 | normal exceptions thrown by compilation may still be initiated when | |
| 103 | the AST object is passed to <tt class="function">compileast()</tt>. This may indicate | |
| 104 | problems not related to syntax (such as a <tt class="exception">MemoryError</tt> | |
| 105 | exception), but may also be due to constructs such as the result of | |
| 106 | parsing <code>del f(0)</code>, which escapes the Python parser but is | |
| 107 | checked by the bytecode compiler. | |
| 108 | ||
| 109 | <P> | |
| 110 | Sequences representing terminal tokens may be represented as either | |
| 111 | two-element lists of the form <code>(1, 'name')</code> or as three-element | |
| 112 | lists of the form <code>(1, 'name', 56)</code>. If the third element is | |
| 113 | present, it is assumed to be a valid line number. The line number | |
| 114 | may be specified for any subset of the terminal symbols in the input | |
| 115 | tree. | |
| 116 | </dl> | |
| 117 | ||
| 118 | <P> | |
| 119 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 120 | <td><nobr><b><tt id='l2h-4941' xml:id='l2h-4941' class="function">tuple2ast</tt></b>(</nobr></td> | |
| 121 | <td><var>sequence</var>)</td></tr></table></dt> | |
| 122 | <dd> | |
| 123 | This is the same function as <tt class="function">sequence2ast()</tt>. This entry point | |
| 124 | is maintained for backward compatibility. | |
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