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<title>18.10 dis -- Disassembler for Python byte code</title>
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<H1><A NAME="SECTION00201000000000000000000">
18.10 <tt class="module">dis</tt> --
         Disassembler for Python byte code</A>
</H1>

<P>
<A NAME="module-dis"></A>

<P>
The <tt class="module">dis</tt> module supports the analysis of Python byte code by
disassembling it.  Since there is no Python assembler, this module
defines the Python assembly language.  The Python byte code which
this module takes as an input is defined in the file
<span class="file">Include/opcode.h</span> and used by the compiler and the interpreter.

<P>
Example: Given the function <tt class="function">myfunc</tt>:

<P>
<div class="verbatim"><pre>
def myfunc(alist):
    return len(alist)
</pre></div>

<P>
the following command can be used to get the disassembly of
<tt class="function">myfunc()</tt>:

<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; dis.dis(myfunc)
  2           0 LOAD_GLOBAL              0 (len)
              3 LOAD_FAST                0 (alist)
              6 CALL_FUNCTION            1
              9 RETURN_VALUE
             10 LOAD_CONST               0 (None)
             13 RETURN_VALUE
</pre></div>

<P>
(The ``2'' is a line number).

<P>
The <tt class="module">dis</tt> module defines the following functions and constants:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5001' xml:id='l2h-5001' class="function">dis</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>bytesource</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Disassemble the <var>bytesource</var> object. <var>bytesource</var> can denote
either a module, a class, a method, a function, or a code object.
For a module, it disassembles all functions.  For a class,
it disassembles all methods.  For a single code sequence, it prints
one line per byte code instruction.  If no object is provided, it
disassembles the last traceback.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5002' xml:id='l2h-5002' class="function">distb</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>tb</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Disassembles the top-of-stack function of a traceback, using the last
traceback if none was passed.  The instruction causing the exception
is indicated.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5003' xml:id='l2h-5003' class="function">disassemble</tt></b>(</nobr></td>
  <td><var>code</var><big>[</big><var>, lasti</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Disassembles a code object, indicating the last instruction if <var>lasti</var>
was provided.  The output is divided in the following columns:

<P>

<OL>
<LI>the line number, for the first instruction of each line
</LI>
<LI>the current instruction, indicated as "<tt class="samp">-&#45;&gt;</tt>",
</LI>
<LI>a labelled instruction, indicated with "<tt class="samp">&gt;<code>&gt;</code></tt>",
</LI>
<LI>the address of the instruction,
</LI>
<LI>the operation code name,
</LI>
<LI>operation parameters, and
</LI>
<LI>interpretation of the parameters in parentheses.
</LI>
</OL>

<P>
The parameter interpretation recognizes local and global
variable names, constant values, branch targets, and compare
operators.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5004' xml:id='l2h-5004' class="function">disco</tt></b>(</nobr></td>
  <td><var>code</var><big>[</big><var>, lasti</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
A synonym for disassemble.  It is more convenient to type, and kept
for compatibility with earlier Python releases.
</dl>

<P>
<dl><dt><b><tt id='l2h-5005' xml:id='l2h-5005'>opname</tt></b></dt>
<dd>
Sequence of operation names, indexable using the byte code.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-5006' xml:id='l2h-5006'>cmp_op</tt></b></dt>
<dd>
Sequence of all compare operation names.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-5007' xml:id='l2h-5007'>hasconst</tt></b></dt>
<dd>
Sequence of byte codes that have a constant parameter.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-5008' xml:id='l2h-5008'>hasfree</tt></b></dt>
<dd>
Sequence of byte codes that access a free variable.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-5009' xml:id='l2h-5009'>hasname</tt></b></dt>
<dd>
Sequence of byte codes that access an attribute by name.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-5010' xml:id='l2h-5010'>hasjrel</tt></b></dt>
<dd>
Sequence of byte codes that have a relative jump target.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-5011' xml:id='l2h-5011'>hasjabs</tt></b></dt>
<dd>
Sequence of byte codes that have an absolute jump target.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-5012' xml:id='l2h-5012'>haslocal</tt></b></dt>
<dd>
Sequence of byte codes that access a local variable.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-5013' xml:id='l2h-5013'>hascompare</tt></b></dt>
<dd>
Sequence of byte codes of Boolean operations.
</dd></dl>

<P>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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