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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(x=None)
Disassemble the *x* object. *x* 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=None)
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=-1)
disco(code, lasti=-1)
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:: findlinestarts(code)
This generator function uses the ``co_firstlineno`` and ``co_lnotab``
attributes of the code object *code* to find the offsets which are starts of
lines in the source code. They are generated as ``(offset, lineno)`` pairs.
.. function:: findlabels(code)
Detect all offsets in the code object *code* which are jump targets, and
return a list of these offsets.
.. 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_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_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_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``.
.. 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:: 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:: SET_ADD (i)
Calls ``set.add(TOS1[-i], TOS)``. Used to implement set comprehensions.
.. opcode:: LIST_APPEND (i)
Calls ``list.append(TOS[-i], TOS)``. Used to implement list comprehensions.
.. opcode:: MAP_ADD (i)
Calls ``dict.setitem(TOS1[-i], TOS, TOS1)``. Used to implement dict
comprehensions.
For all of the SET_ADD, LIST_APPEND and MAP_ADD instructions, while the
added value or key/value pair is popped off, the container object remains on
the stack so that it is available for further iterations of the loop.
.. 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:: 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:: POP_EXCEPT ()
Removes one block from the block stack. The popped block must be an exception
handler block, as implicitly created when entering an except handler.
In addition to popping extraneous values from the frame stack, the
last three popped values are used to restore the exception state.
.. 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:: LOAD_BUILD_CLASS ()
Pushes :func:`builtins.__build_class__` onto the stack. It is later called
by ``CALL_FUNCTION`` to construct a class.
.. 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 TOS 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, TOS is removed from the stack.
If the stack represents an exception, *and* the function call returns
a 'true' value, this information is "zapped" and replaced with a single
``WHY_SILENCED`` to prevent ``END_FINALLY`` from re-raising the exception.
(But non-local gotos will still be resumed.)
.. XXX explain the WHY stuff!
.. opcode:: STORE_LOCALS
Pops TOS from the stack and stores it as the current frame's ``f_locals``.
This is used in class construction.
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_FAST``
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.
.. opcode:: UNPACK_EX (counts)
Implements assignment with a starred target: Unpacks an iterable in TOS into
individual values, where the total number of values can be smaller than the
number of items in the iterable: one the new values will be a list of all
leftover items.
The low byte of *counts* is the number of values before the list value, the
high byte of *counts* the number of values after it. The resulting values
are put onto the stack right-to-left.
.. 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.
.. 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_SET (count)
Works as ``BUILD_TUPLE``, but creates a set.
.. opcode:: BUILD_MAP (count)
Pushes a new dictionary object onto the stack. The dictionary is pre-sized
to hold *count* entries.
.. 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]``. TOS and TOS1 are popped and provide
the *fromlist* and *level* arguments of :func:`__import__`. 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:: POP_JUMP_IF_TRUE (target)
If TOS is true, sets the bytecode counter to *target*. TOS is popped.
.. opcode:: POP_JUMP_IF_FALSE (target)
If TOS is false, sets the bytecode counter to *target*. TOS is popped.
.. opcode:: JUMP_IF_TRUE_OR_POP (target)
If TOS is true, sets the bytecode counter to *target* and leaves TOS
on the stack. Otherwise (TOS is false), TOS is popped.
.. opcode:: JUMP_IF_FALSE_OR_POP (target)
If TOS is false, sets the bytecode counter to *target* and leaves
TOS on the stack. Otherwise (TOS is true), TOS is popped.
.. 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 byte code
counter is incremented by *delta*.
.. opcode:: LOAD_GLOBAL (namei)
Loads the global named ``co_names[namei]`` onto the stack.
.. 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:: STORE_MAP ()
Store a key and value pair in a dictionary. Pops the key and value while leaving
the dictionary on the stack.
.. 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. Pops all function arguments, and
the function itself off the stack, and pushes the return value.
.. 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 *__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 :func:`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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