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:mod:`dis` --- Disassembler for Python bytecode
===============================================
.. module:: dis
:synopsis: Disassembler for Python bytecode.
The :mod:`dis` module supports the analysis of Python :term:`bytecode` by disassembling
it. Since there is no Python assembler, this module defines the Python assembly
language. The Python bytecode which this module takes as an input is defined
in the file :file:`Include/opcode.h` and used by the compiler and the
interpreter.
Example: Given the function :func:`myfunc`::
def myfunc(alist):
return len(alist)
the following command can be used to get the disassembly of :func:`myfunc`::
>>> dis.dis(myfunc)
2 0 LOAD_GLOBAL 0 (len)
3 LOAD_FAST 0 (alist)
6 CALL_FUNCTION 1
9 RETURN_VALUE
(The "2" is a line number).
The :mod:`dis` module defines the following functions and constants:
.. function:: dis([bytesource])
Disassemble the *bytesource* object. *bytesource* 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 bytecode instruction. If no object is
provided, it disassembles the last traceback.
.. function:: distb([tb])
Disassembles the top-of-stack function of a traceback, using the last traceback
if none was passed. The instruction causing the exception is indicated.
.. function:: disassemble(code[, lasti])
Disassembles a code object, indicating the last instruction if *lasti* was
provided. The output is divided in the following columns:
#. the line number, for the first instruction of each line
#. the current instruction, indicated as ``-->``,
#. a labelled instruction, indicated with ``>>``,
#. the address of the instruction,
#. the operation code name,
#. operation parameters, and
#. interpretation of the parameters in parentheses.
The parameter interpretation recognizes local and global variable names,
constant values, branch targets, and compare operators.
.. function:: disco(code[, lasti])
A synonym for disassemble. It is more convenient to type, and kept for
compatibility with earlier Python releases.
.. data:: opname
Sequence of operation names, indexable using the bytecode.
.. data:: opmap
Dictionary mapping bytecodes to operation names.
.. data:: cmp_op
Sequence of all compare operation names.
.. data:: hasconst
Sequence of bytecodes that have a constant parameter.
.. data:: hasfree
Sequence of bytecodes that access a free variable.
.. data:: hasname
Sequence of bytecodes that access an attribute by name.
.. data:: hasjrel
Sequence of bytecodes that have a relative jump target.
.. data:: hasjabs
Sequence of bytecodes that have an absolute jump target.
.. data:: haslocal
Sequence of bytecodes that access a local variable.
.. data:: hascompare
Sequence of bytecodes of Boolean operations.
.. _bytecodes:
Python Bytecode Instructions
----------------------------
The Python compiler currently generates the following bytecode instructions.
.. opcode:: STOP_CODE ()
Indicates end-of-code to the compiler, not used by the interpreter.
.. opcode:: NOP ()
Do nothing code. Used as a placeholder by the bytecode optimizer.
.. opcode:: POP_TOP ()
Removes the top-of-stack (TOS) item.
.. opcode:: ROT_TWO ()
Swaps the two top-most stack items.
.. opcode:: ROT_THREE ()
Lifts second and third stack item one position up, moves top down to position
three.
.. opcode:: ROT_FOUR ()
Lifts second, third and forth stack item one position up, moves top down to
position four.
.. opcode:: DUP_TOP ()
Duplicates the reference on top of the stack.
Unary Operations take the top of the stack, apply the operation, and push the
result back on the stack.
.. opcode:: UNARY_POSITIVE ()
Implements ``TOS = +TOS``.
.. opcode:: UNARY_NEGATIVE ()
Implements ``TOS = -TOS``.
.. opcode:: UNARY_NOT ()
Implements ``TOS = not TOS``.
.. opcode:: UNARY_CONVERT ()
Implements ``TOS = `TOS```.
.. opcode:: UNARY_INVERT ()
Implements ``TOS = ~TOS``.
.. opcode:: GET_ITER ()
Implements ``TOS = iter(TOS)``.
Binary operations remove the top of the stack (TOS) and the second top-most
stack item (TOS1) from the stack. They perform the operation, and put the
result back on the stack.
.. opcode:: BINARY_POWER ()
Implements ``TOS = TOS1 ** TOS``.
.. opcode:: BINARY_MULTIPLY ()
Implements ``TOS = TOS1 * TOS``.
.. opcode:: BINARY_DIVIDE ()
Implements ``TOS = TOS1 / TOS`` when ``from __future__ import division`` is not
in effect.
.. opcode:: BINARY_FLOOR_DIVIDE ()
Implements ``TOS = TOS1 // TOS``.
.. opcode:: BINARY_TRUE_DIVIDE ()
Implements ``TOS = TOS1 / TOS`` when ``from __future__ import division`` is in
effect.
.. opcode:: BINARY_MODULO ()
Implements ``TOS = TOS1 % TOS``.
.. opcode:: BINARY_ADD ()
Implements ``TOS = TOS1 + TOS``.
.. opcode:: BINARY_SUBTRACT ()
Implements ``TOS = TOS1 - TOS``.
.. opcode:: BINARY_SUBSCR ()
Implements ``TOS = TOS1[TOS]``.
.. opcode:: BINARY_LSHIFT ()
Implements ``TOS = TOS1 << TOS``.
.. opcode:: BINARY_RSHIFT ()
Implements ``TOS = TOS1 >> TOS``.
.. opcode:: BINARY_AND ()
Implements ``TOS = TOS1 & TOS``.
.. opcode:: BINARY_XOR ()
Implements ``TOS = TOS1 ^ TOS``.
.. opcode:: BINARY_OR ()
Implements ``TOS = TOS1 | TOS``.
In-place operations are like binary operations, in that they remove TOS and
TOS1, and push the result back on the stack, but the operation is done in-place
when TOS1 supports it, and the resulting TOS may be (but does not have to be)
the original TOS1.
.. opcode:: INPLACE_POWER ()
Implements in-place ``TOS = TOS1 ** TOS``.
.. opcode:: INPLACE_MULTIPLY ()
Implements in-place ``TOS = TOS1 * TOS``.
.. opcode:: INPLACE_DIVIDE ()
Implements in-place ``TOS = TOS1 / TOS`` when ``from __future__ import
division`` is not in effect.
.. opcode:: INPLACE_FLOOR_DIVIDE ()
Implements in-place ``TOS = TOS1 // TOS``.
.. opcode:: INPLACE_TRUE_DIVIDE ()
Implements in-place ``TOS = TOS1 / TOS`` when ``from __future__ import
division`` is in effect.
.. opcode:: INPLACE_MODULO ()
Implements in-place ``TOS = TOS1 % TOS``.
.. opcode:: INPLACE_ADD ()
Implements in-place ``TOS = TOS1 + TOS``.
.. opcode:: INPLACE_SUBTRACT ()
Implements in-place ``TOS = TOS1 - TOS``.
.. opcode:: INPLACE_LSHIFT ()
Implements in-place ``TOS = TOS1 << TOS``.
.. opcode:: INPLACE_RSHIFT ()
Implements in-place ``TOS = TOS1 >> TOS``.
.. opcode:: INPLACE_AND ()
Implements in-place ``TOS = TOS1 & TOS``.
.. opcode:: INPLACE_XOR ()
Implements in-place ``TOS = TOS1 ^ TOS``.
.. opcode:: INPLACE_OR ()
Implements in-place ``TOS = TOS1 | TOS``.
The slice opcodes take up to three parameters.
.. opcode:: SLICE+0 ()
Implements ``TOS = TOS[:]``.
.. opcode:: SLICE+1 ()
Implements ``TOS = TOS1[TOS:]``.
.. opcode:: SLICE+2 ()
Implements ``TOS = TOS1[:TOS]``.
.. opcode:: SLICE+3 ()
Implements ``TOS = TOS2[TOS1:TOS]``.
Slice assignment needs even an additional parameter. As any statement, they put
nothing on the stack.
.. opcode:: STORE_SLICE+0 ()
Implements ``TOS[:] = TOS1``.
.. opcode:: STORE_SLICE+1 ()
Implements ``TOS1[TOS:] = TOS2``.
.. opcode:: STORE_SLICE+2 ()
Implements ``TOS1[:TOS] = TOS2``.
.. opcode:: STORE_SLICE+3 ()
Implements ``TOS2[TOS1:TOS] = TOS3``.
.. opcode:: DELETE_SLICE+0 ()
Implements ``del TOS[:]``.
.. opcode:: DELETE_SLICE+1 ()
Implements ``del TOS1[TOS:]``.
.. opcode:: DELETE_SLICE+2 ()
Implements ``del TOS1[:TOS]``.
.. opcode:: DELETE_SLICE+3 ()
Implements ``del TOS2[TOS1:TOS]``.
.. opcode:: STORE_SUBSCR ()
Implements ``TOS1[TOS] = TOS2``.
.. opcode:: DELETE_SUBSCR ()
Implements ``del TOS1[TOS]``.
Miscellaneous opcodes.
.. opcode:: PRINT_EXPR ()
Implements the expression statement for the interactive mode. TOS is removed
from the stack and printed. In non-interactive mode, an expression statement is
terminated with ``POP_STACK``.
.. opcode:: PRINT_ITEM ()
Prints TOS to the file-like object bound to ``sys.stdout``. There is one such
instruction for each item in the :keyword:`print` statement.
.. opcode:: PRINT_ITEM_TO ()
Like ``PRINT_ITEM``, but prints the item second from TOS to the file-like object
at TOS. This is used by the extended print statement.
.. opcode:: PRINT_NEWLINE ()
Prints a new line on ``sys.stdout``. This is generated as the last operation of
a :keyword:`print` statement, unless the statement ends with a comma.
.. opcode:: PRINT_NEWLINE_TO ()
Like ``PRINT_NEWLINE``, but prints the new line on the file-like object on the
TOS. This is used by the extended print statement.
.. opcode:: BREAK_LOOP ()
Terminates a loop due to a :keyword:`break` statement.
.. opcode:: CONTINUE_LOOP (target)
Continues a loop due to a :keyword:`continue` statement. *target* is the
address to jump to (which should be a ``FOR_ITER`` instruction).
.. opcode:: LIST_APPEND ()
Calls ``list.append(TOS1, TOS)``. Used to implement list comprehensions.
.. opcode:: LOAD_LOCALS ()
Pushes a reference to the locals of the current scope on the stack. This is used
in the code for a class definition: After the class body is evaluated, the
locals are passed to the class definition.
.. opcode:: RETURN_VALUE ()
Returns with TOS to the caller of the function.
.. opcode:: YIELD_VALUE ()
Pops ``TOS`` and yields it from a :term:`generator`.
.. opcode:: IMPORT_STAR ()
Loads all symbols not starting with ``'_'`` directly from the module TOS to the
local namespace. The module is popped after loading all names. This opcode
implements ``from module import *``.
.. opcode:: EXEC_STMT ()
Implements ``exec TOS2,TOS1,TOS``. The compiler fills missing optional
parameters with ``None``.
.. opcode:: POP_BLOCK ()
Removes one block from the block stack. Per frame, there is a stack of blocks,
denoting nested loops, try statements, and such.
.. opcode:: END_FINALLY ()
Terminates a :keyword:`finally` clause. The interpreter recalls whether the
exception has to be re-raised, or whether the function returns, and continues
with the outer-next block.
.. opcode:: BUILD_CLASS ()
Creates a new class object. TOS is the methods dictionary, TOS1 the tuple of
the names of the base classes, and TOS2 the class name.
.. opcode:: WITH_CLEANUP ()
Cleans up the stack when a :keyword:`with` statement block exits. TOS is the
context manager's :meth:`__exit__` bound method. Below that are 1--3 values
indicating how/why the finally clause was entered:
* SECOND = ``None``
* (SECOND, THIRD) = (``WHY_{RETURN,CONTINUE}``), retval
* SECOND = ``WHY_*``; no retval below it
* (SECOND, THIRD, FOURTH) = exc_info()
In the last case, ``TOS(SECOND, THIRD, FOURTH)`` is called, otherwise
``TOS(None, None, None)``.
In addition, if the stack represents an exception, *and* the function call
returns a 'true' value, this information is "zapped", to prevent ``END_FINALLY``
from re-raising the exception. (But non-local gotos should still be resumed.)
.. XXX explain the WHY stuff!
All of the following opcodes expect arguments. An argument is two bytes, with
the more significant byte last.
.. opcode:: STORE_NAME (namei)
Implements ``name = TOS``. *namei* is the index of *name* in the attribute
:attr:`co_names` of the code object. The compiler tries to use ``STORE_LOCAL``
or ``STORE_GLOBAL`` if possible.
.. opcode:: DELETE_NAME (namei)
Implements ``del name``, where *namei* is the index into :attr:`co_names`
attribute of the code object.
.. opcode:: UNPACK_SEQUENCE (count)
Unpacks TOS into *count* individual values, which are put onto the stack
right-to-left.
.. % \begin{opcodedesc}{UNPACK_LIST}{count}
.. % This opcode is obsolete.
.. % \end{opcodedesc}
.. % \begin{opcodedesc}{UNPACK_ARG}{count}
.. % This opcode is obsolete.
.. % \end{opcodedesc}
.. opcode:: DUP_TOPX (count)
Duplicate *count* items, keeping them in the same order. Due to implementation
limits, *count* should be between 1 and 5 inclusive.
.. opcode:: STORE_ATTR (namei)
Implements ``TOS.name = TOS1``, where *namei* is the index of name in
:attr:`co_names`.
.. opcode:: DELETE_ATTR (namei)
Implements ``del TOS.name``, using *namei* as index into :attr:`co_names`.
.. opcode:: STORE_GLOBAL (namei)
Works as ``STORE_NAME``, but stores the name as a global.
.. opcode:: DELETE_GLOBAL (namei)
Works as ``DELETE_NAME``, but deletes a global name.
.. % \begin{opcodedesc}{UNPACK_VARARG}{argc}
.. % This opcode is obsolete.
.. % \end{opcodedesc}
.. opcode:: LOAD_CONST (consti)
Pushes ``co_consts[consti]`` onto the stack.
.. opcode:: LOAD_NAME (namei)
Pushes the value associated with ``co_names[namei]`` onto the stack.
.. opcode:: BUILD_TUPLE (count)
Creates a tuple consuming *count* items from the stack, and pushes the resulting
tuple onto the stack.
.. opcode:: BUILD_LIST (count)
Works as ``BUILD_TUPLE``, but creates a list.
.. opcode:: BUILD_MAP (zero)
Pushes a new empty dictionary object onto the stack. The argument is ignored
and set to zero by the compiler.
.. opcode:: LOAD_ATTR (namei)
Replaces TOS with ``getattr(TOS, co_names[namei])``.
.. opcode:: COMPARE_OP (opname)
Performs a Boolean operation. The operation name can be found in
``cmp_op[opname]``.
.. opcode:: IMPORT_NAME (namei)
Imports the module ``co_names[namei]``. The module object is pushed onto the
stack. The current namespace is not affected: for a proper import statement, a
subsequent ``STORE_FAST`` instruction modifies the namespace.
.. opcode:: IMPORT_FROM (namei)
Loads the attribute ``co_names[namei]`` from the module found in TOS. The
resulting object is pushed onto the stack, to be subsequently stored by a
``STORE_FAST`` instruction.
.. opcode:: JUMP_FORWARD (delta)
Increments bytecode counter by *delta*.
.. opcode:: JUMP_IF_TRUE (delta)
If TOS is true, increment the bytecode counter by *delta*. TOS is left on the
stack.
.. opcode:: JUMP_IF_FALSE (delta)
If TOS is false, increment the bytecode counter by *delta*. TOS is not
changed.
.. opcode:: JUMP_ABSOLUTE (target)
Set bytecode counter to *target*.
.. opcode:: FOR_ITER (delta)
``TOS`` is an :term:`iterator`. Call its :meth:`next` method. If this
yields a new value, push it on the stack (leaving the iterator below it). If
the iterator indicates it is exhausted ``TOS`` is popped, and the bytecode
counter is incremented by *delta*.
.. % \begin{opcodedesc}{FOR_LOOP}{delta}
.. % This opcode is obsolete.
.. % \end{opcodedesc}
.. % \begin{opcodedesc}{LOAD_LOCAL}{namei}
.. % This opcode is obsolete.
.. % \end{opcodedesc}
.. opcode:: LOAD_GLOBAL (namei)
Loads the global named ``co_names[namei]`` onto the stack.
.. % \begin{opcodedesc}{SET_FUNC_ARGS}{argc}
.. % This opcode is obsolete.
.. % \end{opcodedesc}
.. opcode:: SETUP_LOOP (delta)
Pushes a block for a loop onto the block stack. The block spans from the
current instruction with a size of *delta* bytes.
.. opcode:: SETUP_EXCEPT (delta)
Pushes a try block from a try-except clause onto the block stack. *delta* points
to the first except block.
.. opcode:: SETUP_FINALLY (delta)
Pushes a try block from a try-except clause onto the block stack. *delta* points
to the finally block.
.. opcode:: LOAD_FAST (var_num)
Pushes a reference to the local ``co_varnames[var_num]`` onto the stack.
.. opcode:: STORE_FAST (var_num)
Stores TOS into the local ``co_varnames[var_num]``.
.. opcode:: DELETE_FAST (var_num)
Deletes local ``co_varnames[var_num]``.
.. opcode:: LOAD_CLOSURE (i)
Pushes a reference to the cell contained in slot *i* of the cell and free
variable storage. The name of the variable is ``co_cellvars[i]`` if *i* is
less than the length of *co_cellvars*. Otherwise it is ``co_freevars[i -
len(co_cellvars)]``.
.. opcode:: LOAD_DEREF (i)
Loads the cell contained in slot *i* of the cell and free variable storage.
Pushes a reference to the object the cell contains on the stack.
.. opcode:: STORE_DEREF (i)
Stores TOS into the cell contained in slot *i* of the cell and free variable
storage.
.. opcode:: SET_LINENO (lineno)
This opcode is obsolete.
.. opcode:: RAISE_VARARGS (argc)
Raises an exception. *argc* indicates the number of parameters to the raise
statement, ranging from 0 to 3. The handler will find the traceback as TOS2,
the parameter as TOS1, and the exception as TOS.
.. opcode:: CALL_FUNCTION (argc)
Calls a function. The low byte of *argc* indicates the number of positional
parameters, the high byte the number of keyword parameters. On the stack, the
opcode finds the keyword parameters first. For each keyword argument, the value
is on top of the key. Below the keyword parameters, the positional parameters
are on the stack, with the right-most parameter on top. Below the parameters,
the function object to call is on the stack.
.. opcode:: MAKE_FUNCTION (argc)
Pushes a new function object on the stack. TOS is the code associated with the
function. The function object is defined to have *argc* default parameters,
which are found below TOS.
.. opcode:: MAKE_CLOSURE (argc)
Creates a new function object, sets its *func_closure* slot, and pushes it on
the stack. TOS is the code associated with the function, TOS1 the tuple
containing cells for the closure's free variables. The function also has
*argc* default parameters, which are found below the cells.
.. opcode:: BUILD_SLICE (argc)
.. index:: builtin: slice
Pushes a slice object on the stack. *argc* must be 2 or 3. If it is 2,
``slice(TOS1, TOS)`` is pushed; if it is 3, ``slice(TOS2, TOS1, TOS)`` is
pushed. See the ``slice()`` built-in function for more information.
.. opcode:: EXTENDED_ARG (ext)
Prefixes any opcode which has an argument too big to fit into the default two
bytes. *ext* holds two additional bytes which, taken together with the
subsequent opcode's argument, comprise a four-byte argument, *ext* being the two
most-significant bytes.
.. opcode:: CALL_FUNCTION_VAR (argc)
Calls a function. *argc* is interpreted as in ``CALL_FUNCTION``. The top element
on the stack contains the variable argument list, followed by keyword and
positional arguments.
.. opcode:: CALL_FUNCTION_KW (argc)
Calls a function. *argc* is interpreted as in ``CALL_FUNCTION``. The top element
on the stack contains the keyword arguments dictionary, followed by explicit
keyword and positional arguments.
.. opcode:: CALL_FUNCTION_VAR_KW (argc)
Calls a function. *argc* is interpreted as in ``CALL_FUNCTION``. The top
element on the stack contains the keyword arguments dictionary, followed by the
variable-arguments tuple, followed by explicit keyword and positional arguments.
.. opcode:: HAVE_ARGUMENT ()
This is not really an opcode. It identifies the dividing line between opcodes
which don't take arguments ``< HAVE_ARGUMENT`` and those which do ``>=
HAVE_ARGUMENT``.
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