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| 54 | ||
| 55 | <H1><A NAME="SECTION0052600000000000000000"> | |
| 56 | 3.26 <tt class="module">codeop</tt> -- | |
| 57 | Compile Python code</A> | |
| 58 | </H1> | |
| 59 | ||
| 60 | <P> | |
| 61 | <A NAME="module-codeop"></A> | |
| 62 | ||
| 63 | <P> | |
| 64 | The <tt class="module">codeop</tt> module provides utilities upon which the Python | |
| 65 | read-eval-print loop can be emulated, as is done in the | |
| 66 | <tt class="module"><a href="module-code.html">code</a></tt> module. As a result, you probably don't want to use | |
| 67 | the module directly; if you want to include such a loop in your | |
| 68 | program you probably want to use the <tt class="module"><a href="module-code.html">code</a></tt> module instead. | |
| 69 | ||
| 70 | <P> | |
| 71 | There are two parts to this job: | |
| 72 | ||
| 73 | <P> | |
| 74 | ||
| 75 | <OL> | |
| 76 | <LI>Being able to tell if a line of input completes a Python | |
| 77 | statement: in short, telling whether to print | |
| 78 | `<code>><code>></code>> </code>' or `<code>... </code>' next. | |
| 79 | </LI> | |
| 80 | <LI>Remembering which future statements the user has entered, so | |
| 81 | subsequent input can be compiled with these in effect. | |
| 82 | </LI> | |
| 83 | </OL> | |
| 84 | ||
| 85 | <P> | |
| 86 | The <tt class="module">codeop</tt> module provides a way of doing each of these | |
| 87 | things, and a way of doing them both. | |
| 88 | ||
| 89 | <P> | |
| 90 | To do just the former: | |
| 91 | ||
| 92 | <P> | |
| 93 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 94 | <td><nobr><b><tt id='l2h-758' xml:id='l2h-758' class="function">compile_command</tt></b>(</nobr></td> | |
| 95 | <td><var>source</var><big>[</big><var>, filename</var><big>[</big><var>, symbol</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> | |
| 96 | <dd> | |
| 97 | Tries to compile <var>source</var>, which should be a string of Python | |
| 98 | code and return a code object if <var>source</var> is valid | |
| 99 | Python code. In that case, the filename attribute of the code object | |
| 100 | will be <var>filename</var>, which defaults to <code>'<input>'</code>. | |
| 101 | Returns <code>None</code> if <var>source</var> is <em>not</em> valid Python | |
| 102 | code, but is a prefix of valid Python code. | |
| 103 | ||
| 104 | <P> | |
| 105 | If there is a problem with <var>source</var>, an exception will be raised. | |
| 106 | <tt class="exception">SyntaxError</tt> is raised if there is invalid Python syntax, | |
| 107 | and <tt class="exception">OverflowError</tt> or <tt class="exception">ValueError</tt> if there is an | |
| 108 | invalid literal. | |
| 109 | ||
| 110 | <P> | |
| 111 | The <var>symbol</var> argument determines whether <var>source</var> is compiled | |
| 112 | as a statement (<code>'single'</code>, the default) or as an expression | |
| 113 | (<code>'eval'</code>). Any other value will cause <tt class="exception">ValueError</tt> to | |
| 114 | be raised. | |
| 115 | ||
| 116 | <P> | |
| 117 | <strong>Caveat:</strong> | |
| 118 | It is possible (but not likely) that the parser stops parsing | |
| 119 | with a successful outcome before reaching the end of the source; | |
| 120 | in this case, trailing symbols may be ignored instead of causing an | |
| 121 | error. For example, a backslash followed by two newlines may be | |
| 122 | followed by arbitrary garbage. This will be fixed once the API | |
| 123 | for the parser is better. | |
| 124 | </dl> | |
| 125 | ||
| 126 | <P> | |
| 127 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 128 | <td><nobr><b><span class="typelabel">class</span> <tt id='l2h-759' xml:id='l2h-759' class="class">Compile</tt></b>(</nobr></td> | |
| 129 | <td><var></var>)</td></tr></table></dt> | |
| 130 | <dd> | |
| 131 | Instances of this class have <tt class="method">__call__()</tt> methods identical in | |
| 132 | signature to the built-in function <tt class="function">compile()</tt>, but with the | |
| 133 | difference that if the instance compiles program text containing a | |
| 134 | <tt class="module">__future__</tt> statement, the instance 'remembers' and compiles | |
| 135 | all subsequent program texts with the statement in force. | |
| 136 | </dl> | |
| 137 | ||
| 138 | <P> | |
| 139 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 140 | <td><nobr><b><span class="typelabel">class</span> <tt id='l2h-760' xml:id='l2h-760' class="class">CommandCompiler</tt></b>(</nobr></td> | |
| 141 | <td><var></var>)</td></tr></table></dt> | |
| 142 | <dd> | |
| 143 | Instances of this class have <tt class="method">__call__()</tt> methods identical in | |
| 144 | signature to <tt class="function">compile_command()</tt>; the difference is that if | |
| 145 | the instance compiles program text containing a <code>__future__</code> | |
| 146 | statement, the instance 'remembers' and compiles all subsequent | |
| 147 | program texts with the statement in force. | |
| 148 | </dl> | |
| 149 | ||
| 150 | <P> | |
| 151 | A note on version compatibility: the <tt class="class">Compile</tt> and | |
| 152 | <tt class="class">CommandCompiler</tt> are new in Python 2.2. If you want to enable | |
| 153 | the future-tracking features of 2.2 but also retain compatibility with | |
| 154 | 2.1 and earlier versions of Python you can either write | |
| 155 | ||
| 156 | <P> | |
| 157 | <div class="verbatim"><pre> | |
| 158 | try: | |
| 159 | from codeop import CommandCompiler | |
| 160 | compile_command = CommandCompiler() | |
| 161 | del CommandCompiler | |
| 162 | except ImportError: | |
| 163 | from codeop import compile_command | |
| 164 | </pre></div> | |
| 165 | ||
| 166 | <P> | |
| 167 | which is a low-impact change, but introduces possibly unwanted global | |
| 168 | state into your program, or you can write: | |
| 169 | ||
| 170 | <P> | |
| 171 | <div class="verbatim"><pre> | |
| 172 | try: | |
| 173 | from codeop import CommandCompiler | |
| 174 | except ImportError: | |
| 175 | def CommandCompiler(): | |
| 176 | from codeop import compile_command | |
| 177 | return compile_command | |
| 178 | </pre></div> | |
| 179 | ||
| 180 | <P> | |
| 181 | and then call <code>CommandCompiler</code> every time you need a fresh | |
| 182 | compiler object. | |
| 183 | ||
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| 218 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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