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| 55 | <H1><A NAME="SECTION0051200000000000000000"> |
| 56 | 3.12 <tt class="module">traceback</tt> -- |
| 57 | Print or retrieve a stack traceback</A> |
| 58 | </H1> |
| 59 | |
| 60 | <P> |
| 61 | <A NAME="module-traceback"></A> |
| 62 | |
| 63 | <P> |
| 64 | This module provides a standard interface to extract, format and print |
| 65 | stack traces of Python programs. It exactly mimics the behavior of |
| 66 | the Python interpreter when it prints a stack trace. This is useful |
| 67 | when you want to print stack traces under program control, such as in a |
| 68 | ``wrapper'' around the interpreter. |
| 69 | |
| 70 | <P> |
| 71 | The module uses traceback objects -- this is the object type that is |
| 72 | stored in the variables <code>sys.exc_traceback</code> (deprecated) and |
| 73 | <code>sys.last_traceback</code> and returned as the third item from |
| 74 | <tt class="function">sys.exc_info()</tt>. |
| 75 | <a id='l2h-605' xml:id='l2h-605'></a> |
| 76 | <P> |
| 77 | The module defines the following functions: |
| 78 | |
| 79 | <P> |
| 80 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 81 | <td><nobr><b><tt id='l2h-606' xml:id='l2h-606' class="function">print_tb</tt></b>(</nobr></td> |
| 82 | <td><var>traceback</var><big>[</big><var>, limit</var><big>[</big><var>, file</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 83 | <dd> |
| 84 | Print up to <var>limit</var> stack trace entries from <var>traceback</var>. If |
| 85 | <var>limit</var> is omitted or <code>None</code>, all entries are printed. |
| 86 | If <var>file</var> is omitted or <code>None</code>, the output goes to |
| 87 | <code>sys.stderr</code>; otherwise it should be an open file or file-like |
| 88 | object to receive the output. |
| 89 | </dl> |
| 90 | |
| 91 | <P> |
| 92 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 93 | <td><nobr><b><tt id='l2h-607' xml:id='l2h-607' class="function">print_exception</tt></b>(</nobr></td> |
| 94 | <td><var>type, value, traceback</var><big>[</big><var>, |
| 95 | limit</var><big>[</big><var>, file</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 96 | <dd> |
| 97 | Print exception information and up to <var>limit</var> stack trace entries |
| 98 | from <var>traceback</var> to <var>file</var>. |
| 99 | This differs from <tt class="function">print_tb()</tt> in the |
| 100 | following ways: (1) if <var>traceback</var> is not <code>None</code>, it prints a |
| 101 | header "<tt class="samp">Traceback (most recent call last):</tt>"; (2) it prints the |
| 102 | exception <var>type</var> and <var>value</var> after the stack trace; (3) if |
| 103 | <var>type</var> is <tt class="exception">SyntaxError</tt> and <var>value</var> has the |
| 104 | appropriate format, it prints the line where the syntax error occurred |
| 105 | with a caret indicating the approximate position of the error. |
| 106 | </dl> |
| 107 | |
| 108 | <P> |
| 109 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 110 | <td><nobr><b><tt id='l2h-608' xml:id='l2h-608' class="function">print_exc</tt></b>(</nobr></td> |
| 111 | <td><var></var><big>[</big><var>limit</var><big>[</big><var>, file</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 112 | <dd> |
| 113 | This is a shorthand for <code>print_exception(sys.exc_type, |
| 114 | sys.exc_value, sys.exc_traceback, <var>limit</var>, <var>file</var>)</code>. (In |
| 115 | fact, it uses <tt class="function">sys.exc_info()</tt> to retrieve the same |
| 116 | information in a thread-safe way instead of using the deprecated |
| 117 | variables.) |
| 118 | </dl> |
| 119 | |
| 120 | <P> |
| 121 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 122 | <td><nobr><b><tt id='l2h-609' xml:id='l2h-609' class="function">format_exc</tt></b>(</nobr></td> |
| 123 | <td><var></var><big>[</big><var>limit</var><big>[</big><var>, file</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 124 | <dd> |
| 125 | This is like <code>print_exc(<var>limit</var>)</code> but returns a string |
| 126 | instead of printing to a file. |
| 127 | |
| 128 | <span class="versionnote">New in version 2.4.</span> |
| 129 | |
| 130 | </dl> |
| 131 | |
| 132 | <P> |
| 133 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 134 | <td><nobr><b><tt id='l2h-610' xml:id='l2h-610' class="function">print_last</tt></b>(</nobr></td> |
| 135 | <td><var></var><big>[</big><var>limit</var><big>[</big><var>, file</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 136 | <dd> |
| 137 | This is a shorthand for <code>print_exception(sys.last_type, |
| 138 | sys.last_value, sys.last_traceback, <var>limit</var>, <var>file</var>)</code>. |
| 139 | </dl> |
| 140 | |
| 141 | <P> |
| 142 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 143 | <td><nobr><b><tt id='l2h-611' xml:id='l2h-611' class="function">print_stack</tt></b>(</nobr></td> |
| 144 | <td><var></var><big>[</big><var>f</var><big>[</big><var>, limit</var><big>[</big><var>, file</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 145 | <dd> |
| 146 | This function prints a stack trace from its invocation point. The |
| 147 | optional <var>f</var> argument can be used to specify an alternate stack |
| 148 | frame to start. The optional <var>limit</var> and <var>file</var> arguments have the |
| 149 | same meaning as for <tt class="function">print_exception()</tt>. |
| 150 | </dl> |
| 151 | |
| 152 | <P> |
| 153 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 154 | <td><nobr><b><tt id='l2h-612' xml:id='l2h-612' class="function">extract_tb</tt></b>(</nobr></td> |
| 155 | <td><var>traceback</var><big>[</big><var>, limit</var><big>]</big><var></var>)</td></tr></table></dt> |
| 156 | <dd> |
| 157 | Return a list of up to <var>limit</var> ``pre-processed'' stack trace |
| 158 | entries extracted from the traceback object <var>traceback</var>. It is |
| 159 | useful for alternate formatting of stack traces. If <var>limit</var> is |
| 160 | omitted or <code>None</code>, all entries are extracted. A |
| 161 | ``pre-processed'' stack trace entry is a quadruple (<var>filename</var>, |
| 162 | <var>line number</var>, <var>function name</var>, <var>text</var>) representing |
| 163 | the information that is usually printed for a stack trace. The |
| 164 | <var>text</var> is a string with leading and trailing whitespace |
| 165 | stripped; if the source is not available it is <code>None</code>. |
| 166 | </dl> |
| 167 | |
| 168 | <P> |
| 169 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 170 | <td><nobr><b><tt id='l2h-613' xml:id='l2h-613' class="function">extract_stack</tt></b>(</nobr></td> |
| 171 | <td><var></var><big>[</big><var>f</var><big>[</big><var>, limit</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 172 | <dd> |
| 173 | Extract the raw traceback from the current stack frame. The return |
| 174 | value has the same format as for <tt class="function">extract_tb()</tt>. The |
| 175 | optional <var>f</var> and <var>limit</var> arguments have the same meaning as |
| 176 | for <tt class="function">print_stack()</tt>. |
| 177 | </dl> |
| 178 | |
| 179 | <P> |
| 180 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 181 | <td><nobr><b><tt id='l2h-614' xml:id='l2h-614' class="function">format_list</tt></b>(</nobr></td> |
| 182 | <td><var>list</var>)</td></tr></table></dt> |
| 183 | <dd> |
| 184 | Given a list of tuples as returned by <tt class="function">extract_tb()</tt> or |
| 185 | <tt class="function">extract_stack()</tt>, return a list of strings ready for |
| 186 | printing. Each string in the resulting list corresponds to the item |
| 187 | with the same index in the argument list. Each string ends in a |
| 188 | newline; the strings may contain internal newlines as well, for those |
| 189 | items whose source text line is not <code>None</code>. |
| 190 | </dl> |
| 191 | |
| 192 | <P> |
| 193 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 194 | <td><nobr><b><tt id='l2h-615' xml:id='l2h-615' class="function">format_exception_only</tt></b>(</nobr></td> |
| 195 | <td><var>type, value</var>)</td></tr></table></dt> |
| 196 | <dd> |
| 197 | Format the exception part of a traceback. The arguments are the |
| 198 | exception type and value such as given by <code>sys.last_type</code> and |
| 199 | <code>sys.last_value</code>. The return value is a list of strings, each |
| 200 | ending in a newline. Normally, the list contains a single string; |
| 201 | however, for <tt class="exception">SyntaxError</tt> exceptions, it contains several |
| 202 | lines that (when printed) display detailed information about where the |
| 203 | syntax error occurred. The message indicating which exception |
| 204 | occurred is the always last string in the list. |
| 205 | </dl> |
| 206 | |
| 207 | <P> |
| 208 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 209 | <td><nobr><b><tt id='l2h-616' xml:id='l2h-616' class="function">format_exception</tt></b>(</nobr></td> |
| 210 | <td><var>type, value, tb</var><big>[</big><var>, limit</var><big>]</big><var></var>)</td></tr></table></dt> |
| 211 | <dd> |
| 212 | Format a stack trace and the exception information. The arguments |
| 213 | have the same meaning as the corresponding arguments to |
| 214 | <tt class="function">print_exception()</tt>. The return value is a list of strings, |
| 215 | each ending in a newline and some containing internal newlines. When |
| 216 | these lines are concatenated and printed, exactly the same text is |
| 217 | printed as does <tt class="function">print_exception()</tt>. |
| 218 | </dl> |
| 219 | |
| 220 | <P> |
| 221 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 222 | <td><nobr><b><tt id='l2h-617' xml:id='l2h-617' class="function">format_tb</tt></b>(</nobr></td> |
| 223 | <td><var>tb</var><big>[</big><var>, limit</var><big>]</big><var></var>)</td></tr></table></dt> |
| 224 | <dd> |
| 225 | A shorthand for <code>format_list(extract_tb(<var>tb</var>, <var>limit</var>))</code>. |
| 226 | </dl> |
| 227 | |
| 228 | <P> |
| 229 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 230 | <td><nobr><b><tt id='l2h-618' xml:id='l2h-618' class="function">format_stack</tt></b>(</nobr></td> |
| 231 | <td><var></var><big>[</big><var>f</var><big>[</big><var>, limit</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 232 | <dd> |
| 233 | A shorthand for <code>format_list(extract_stack(<var>f</var>, <var>limit</var>))</code>. |
| 234 | </dl> |
| 235 | |
| 236 | <P> |
| 237 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 238 | <td><nobr><b><tt id='l2h-619' xml:id='l2h-619' class="function">tb_lineno</tt></b>(</nobr></td> |
| 239 | <td><var>tb</var>)</td></tr></table></dt> |
| 240 | <dd> |
| 241 | This function returns the current line number set in the traceback |
| 242 | object. This function was necessary because in versions of Python |
| 243 | prior to 2.3 when the <b class="programopt">-O</b> flag was passed to Python the |
| 244 | <code><var>tb</var>.tb_lineno</code> was not updated correctly. This function |
| 245 | has no use in versions past 2.3. |
| 246 | </dl> |
| 247 | |
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