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:mod:`dis` --- Disassembler for Python bytecode
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===============================================
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:synopsis: Disassembler for Python bytecode.
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**Source code:** :source:`Lib/dis.py`
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The :mod:`dis` module supports the analysis of CPython :term:`bytecode` by
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disassembling it. The CPython bytecode which this module takes as an input is
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defined in the file :file:`Include/opcode.h` and used by the compiler and the
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Bytecode is an implementation detail of the CPython interpreter! No
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guarantees are made that bytecode will not be added, removed, or changed
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between versions of Python. Use of this module should not be considered to
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work across Python VMs or Python releases.
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Example: Given the function :func:`myfunc`::
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the following command can be used to get the disassembly of :func:`myfunc`::
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2 0 LOAD_GLOBAL 0 (len)
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(The "2" is a line number).
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The :mod:`dis` module defines the following functions and constants:
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.. function:: dis([bytesource])
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Disassemble the *bytesource* object. *bytesource* can denote either a module,
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a class, a method, a function, or a code object. For a module, it
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disassembles all functions. For a class, it disassembles all methods. For a
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single code sequence, it prints one line per bytecode instruction. If no
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object is provided, it disassembles the last traceback.
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.. function:: distb([tb])
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Disassembles the top-of-stack function of a traceback, using the last
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traceback if none was passed. The instruction causing the exception is
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.. function:: disassemble(code[, lasti])
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Disassembles a code object, indicating the last instruction if *lasti* was
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provided. The output is divided in the following columns:
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#. the line number, for the first instruction of each line
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#. the current instruction, indicated as ``-->``,
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#. a labelled instruction, indicated with ``>>``,
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#. the address of the instruction,
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#. the operation code name,
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#. operation parameters, and
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#. interpretation of the parameters in parentheses.
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The parameter interpretation recognizes local and global variable names,
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constant values, branch targets, and compare operators.
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.. function:: disco(code[, lasti])
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A synonym for :func:`disassemble`. It is more convenient to type, and kept
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for compatibility with earlier Python releases.
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.. function:: findlinestarts(code)
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This generator function uses the ``co_firstlineno`` and ``co_lnotab``
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attributes of the code object *code* to find the offsets which are starts of
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lines in the source code. They are generated as ``(offset, lineno)`` pairs.
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.. function:: findlabels(code)
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Detect all offsets in the code object *code* which are jump targets, and
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return a list of these offsets.
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Sequence of operation names, indexable using the bytecode.
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Dictionary mapping operation names to bytecodes.
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Sequence of all compare operation names.
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Sequence of bytecodes that have a constant parameter.
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Sequence of bytecodes that access a free variable.
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Sequence of bytecodes that access an attribute by name.
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Sequence of bytecodes that have a relative jump target.
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Sequence of bytecodes that have an absolute jump target.
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Sequence of bytecodes that access a local variable.
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Sequence of bytecodes of Boolean operations.
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Python Bytecode Instructions
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----------------------------
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The Python compiler currently generates the following bytecode instructions.
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.. opcode:: STOP_CODE ()
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Indicates end-of-code to the compiler, not used by the interpreter.
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Do nothing code. Used as a placeholder by the bytecode optimizer.
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.. opcode:: POP_TOP ()
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Removes the top-of-stack (TOS) item.
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.. opcode:: ROT_TWO ()
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Swaps the two top-most stack items.
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.. opcode:: ROT_THREE ()
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Lifts second and third stack item one position up, moves top down to position
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.. opcode:: ROT_FOUR ()
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Lifts second, third and forth stack item one position up, moves top down to
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.. opcode:: DUP_TOP ()
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Duplicates the reference on top of the stack.
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Unary Operations take the top of the stack, apply the operation, and push the
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result back on the stack.
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.. opcode:: UNARY_POSITIVE ()
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Implements ``TOS = +TOS``.
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.. opcode:: UNARY_NEGATIVE ()
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Implements ``TOS = -TOS``.
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.. opcode:: UNARY_NOT ()
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Implements ``TOS = not TOS``.
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.. opcode:: UNARY_CONVERT ()
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Implements ``TOS = `TOS```.
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.. opcode:: UNARY_INVERT ()
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Implements ``TOS = ~TOS``.
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.. opcode:: GET_ITER ()
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Implements ``TOS = iter(TOS)``.
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Binary operations remove the top of the stack (TOS) and the second top-most
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stack item (TOS1) from the stack. They perform the operation, and put the
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result back on the stack.
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.. opcode:: BINARY_POWER ()
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Implements ``TOS = TOS1 ** TOS``.
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.. opcode:: BINARY_MULTIPLY ()
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Implements ``TOS = TOS1 * TOS``.
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.. opcode:: BINARY_DIVIDE ()
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Implements ``TOS = TOS1 / TOS`` when ``from __future__ import division`` is
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.. opcode:: BINARY_FLOOR_DIVIDE ()
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Implements ``TOS = TOS1 // TOS``.
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.. opcode:: BINARY_TRUE_DIVIDE ()
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Implements ``TOS = TOS1 / TOS`` when ``from __future__ import division`` is
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.. opcode:: BINARY_MODULO ()
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Implements ``TOS = TOS1 % TOS``.
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.. opcode:: BINARY_ADD ()
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Implements ``TOS = TOS1 + TOS``.
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.. opcode:: BINARY_SUBTRACT ()
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Implements ``TOS = TOS1 - TOS``.
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.. opcode:: BINARY_SUBSCR ()
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Implements ``TOS = TOS1[TOS]``.
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.. opcode:: BINARY_LSHIFT ()
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Implements ``TOS = TOS1 << TOS``.
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.. opcode:: BINARY_RSHIFT ()
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Implements ``TOS = TOS1 >> TOS``.
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.. opcode:: BINARY_AND ()
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Implements ``TOS = TOS1 & TOS``.
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.. opcode:: BINARY_XOR ()
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Implements ``TOS = TOS1 ^ TOS``.
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.. opcode:: BINARY_OR ()
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Implements ``TOS = TOS1 | TOS``.
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In-place operations are like binary operations, in that they remove TOS and
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TOS1, and push the result back on the stack, but the operation is done in-place
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when TOS1 supports it, and the resulting TOS may be (but does not have to be)
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.. opcode:: INPLACE_POWER ()
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Implements in-place ``TOS = TOS1 ** TOS``.
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.. opcode:: INPLACE_MULTIPLY ()
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Implements in-place ``TOS = TOS1 * TOS``.
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.. opcode:: INPLACE_DIVIDE ()
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Implements in-place ``TOS = TOS1 / TOS`` when ``from __future__ import
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division`` is not in effect.
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.. opcode:: INPLACE_FLOOR_DIVIDE ()
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Implements in-place ``TOS = TOS1 // TOS``.
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.. opcode:: INPLACE_TRUE_DIVIDE ()
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Implements in-place ``TOS = TOS1 / TOS`` when ``from __future__ import
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division`` is in effect.
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.. opcode:: INPLACE_MODULO ()
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Implements in-place ``TOS = TOS1 % TOS``.
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.. opcode:: INPLACE_ADD ()
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Implements in-place ``TOS = TOS1 + TOS``.
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.. opcode:: INPLACE_SUBTRACT ()
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Implements in-place ``TOS = TOS1 - TOS``.
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.. opcode:: INPLACE_LSHIFT ()
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Implements in-place ``TOS = TOS1 << TOS``.
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.. opcode:: INPLACE_RSHIFT ()
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Implements in-place ``TOS = TOS1 >> TOS``.
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.. opcode:: INPLACE_AND ()
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Implements in-place ``TOS = TOS1 & TOS``.
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.. opcode:: INPLACE_XOR ()
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Implements in-place ``TOS = TOS1 ^ TOS``.
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.. opcode:: INPLACE_OR ()
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Implements in-place ``TOS = TOS1 | TOS``.
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The slice opcodes take up to three parameters.
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.. opcode:: SLICE+0 ()
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Implements ``TOS = TOS[:]``.
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.. opcode:: SLICE+1 ()
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Implements ``TOS = TOS1[TOS:]``.
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.. opcode:: SLICE+2 ()
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Implements ``TOS = TOS1[:TOS]``.
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.. opcode:: SLICE+3 ()
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Implements ``TOS = TOS2[TOS1:TOS]``.
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Slice assignment needs even an additional parameter. As any statement, they put
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nothing on the stack.
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.. opcode:: STORE_SLICE+0 ()
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Implements ``TOS[:] = TOS1``.
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.. opcode:: STORE_SLICE+1 ()
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Implements ``TOS1[TOS:] = TOS2``.
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.. opcode:: STORE_SLICE+2 ()
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Implements ``TOS1[:TOS] = TOS2``.
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.. opcode:: STORE_SLICE+3 ()
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Implements ``TOS2[TOS1:TOS] = TOS3``.
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.. opcode:: DELETE_SLICE+0 ()
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Implements ``del TOS[:]``.
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.. opcode:: DELETE_SLICE+1 ()
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Implements ``del TOS1[TOS:]``.
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.. opcode:: DELETE_SLICE+2 ()
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Implements ``del TOS1[:TOS]``.
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.. opcode:: DELETE_SLICE+3 ()
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Implements ``del TOS2[TOS1:TOS]``.
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.. opcode:: STORE_SUBSCR ()
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Implements ``TOS1[TOS] = TOS2``.
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.. opcode:: DELETE_SUBSCR ()
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Implements ``del TOS1[TOS]``.
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Miscellaneous opcodes.
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.. opcode:: PRINT_EXPR ()
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Implements the expression statement for the interactive mode. TOS is removed
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from the stack and printed. In non-interactive mode, an expression statement
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is terminated with :opcode:`POP_TOP`.
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.. opcode:: PRINT_ITEM ()
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Prints TOS to the file-like object bound to ``sys.stdout``. There is one
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such instruction for each item in the :keyword:`print` statement.
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.. opcode:: PRINT_ITEM_TO ()
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Like ``PRINT_ITEM``, but prints the item second from TOS to the file-like
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object at TOS. This is used by the extended print statement.
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.. opcode:: PRINT_NEWLINE ()
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Prints a new line on ``sys.stdout``. This is generated as the last operation
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of a :keyword:`print` statement, unless the statement ends with a comma.
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.. opcode:: PRINT_NEWLINE_TO ()
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Like ``PRINT_NEWLINE``, but prints the new line on the file-like object on
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the TOS. This is used by the extended print statement.
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.. opcode:: BREAK_LOOP ()
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Terminates a loop due to a :keyword:`break` statement.
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.. opcode:: CONTINUE_LOOP (target)
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Continues a loop due to a :keyword:`continue` statement. *target* is the
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address to jump to (which should be a :opcode:`FOR_ITER` instruction).
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.. opcode:: LIST_APPEND (i)
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Calls ``list.append(TOS[-i], TOS)``. Used to implement list comprehensions.
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While the appended value is popped off, the list object remains on the stack
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so that it is available for further iterations of the loop.
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.. opcode:: LOAD_LOCALS ()
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Pushes a reference to the locals of the current scope on the stack. This is
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used in the code for a class definition: After the class body is evaluated,
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the locals are passed to the class definition.
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.. opcode:: RETURN_VALUE ()
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Returns with TOS to the caller of the function.
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.. opcode:: YIELD_VALUE ()
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Pops ``TOS`` and yields it from a :term:`generator`.
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.. opcode:: IMPORT_STAR ()
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Loads all symbols not starting with ``'_'`` directly from the module TOS to
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the local namespace. The module is popped after loading all names. This
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opcode implements ``from module import *``.
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.. opcode:: EXEC_STMT ()
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Implements ``exec TOS2,TOS1,TOS``. The compiler fills missing optional
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parameters with ``None``.
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.. opcode:: POP_BLOCK ()
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Removes one block from the block stack. Per frame, there is a stack of
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blocks, denoting nested loops, try statements, and such.
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.. opcode:: END_FINALLY ()
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Terminates a :keyword:`finally` clause. The interpreter recalls whether the
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exception has to be re-raised, or whether the function returns, and continues
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with the outer-next block.
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.. opcode:: BUILD_CLASS ()
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Creates a new class object. TOS is the methods dictionary, TOS1 the tuple of
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the names of the base classes, and TOS2 the class name.
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.. opcode:: SETUP_WITH (delta)
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This opcode performs several operations before a with block starts. First,
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it loads :meth:`~object.__exit__` from the context manager and pushes it onto
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the stack for later use by :opcode:`WITH_CLEANUP`. Then,
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:meth:`~object.__enter__` is called, and a finally block pointing to *delta*
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is pushed. Finally, the result of calling the enter method is pushed onto
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the stack. The next opcode will either ignore it (:opcode:`POP_TOP`), or
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store it in (a) variable(s) (:opcode:`STORE_FAST`, :opcode:`STORE_NAME`, or
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:opcode:`UNPACK_SEQUENCE`).
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.. opcode:: WITH_CLEANUP ()
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Cleans up the stack when a :keyword:`with` statement block exits. On top of
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the stack are 1--3 values indicating how/why the finally clause was entered:
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* (TOP, SECOND) = (``WHY_{RETURN,CONTINUE}``), retval
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* TOP = ``WHY_*``; no retval below it
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* (TOP, SECOND, THIRD) = exc_info()
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Under them is EXIT, the context manager's :meth:`__exit__` bound method.
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In the last case, ``EXIT(TOP, SECOND, THIRD)`` is called, otherwise
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``EXIT(None, None, None)``.
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EXIT is removed from the stack, leaving the values above it in the same
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order. In addition, if the stack represents an exception, *and* the function
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call returns a 'true' value, this information is "zapped", to prevent
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``END_FINALLY`` from re-raising the exception. (But non-local gotos should
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.. XXX explain the WHY stuff!
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All of the following opcodes expect arguments. An argument is two bytes, with
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the more significant byte last.
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.. opcode:: STORE_NAME (namei)
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Implements ``name = TOS``. *namei* is the index of *name* in the attribute
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:attr:`co_names` of the code object. The compiler tries to use ``STORE_FAST``
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or ``STORE_GLOBAL`` if possible.
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.. opcode:: DELETE_NAME (namei)
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Implements ``del name``, where *namei* is the index into :attr:`co_names`
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attribute of the code object.
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.. opcode:: UNPACK_SEQUENCE (count)
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Unpacks TOS into *count* individual values, which are put onto the stack
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.. opcode:: DUP_TOPX (count)
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Duplicate *count* items, keeping them in the same order. Due to
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implementation limits, *count* should be between 1 and 5 inclusive.
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.. opcode:: STORE_ATTR (namei)
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Implements ``TOS.name = TOS1``, where *namei* is the index of name in
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.. opcode:: DELETE_ATTR (namei)
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Implements ``del TOS.name``, using *namei* as index into :attr:`co_names`.
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.. opcode:: STORE_GLOBAL (namei)
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Works as ``STORE_NAME``, but stores the name as a global.
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.. opcode:: DELETE_GLOBAL (namei)
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Works as ``DELETE_NAME``, but deletes a global name.
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.. opcode:: LOAD_CONST (consti)
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Pushes ``co_consts[consti]`` onto the stack.
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.. opcode:: LOAD_NAME (namei)
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Pushes the value associated with ``co_names[namei]`` onto the stack.
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.. opcode:: BUILD_TUPLE (count)
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Creates a tuple consuming *count* items from the stack, and pushes the
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resulting tuple onto the stack.
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.. opcode:: BUILD_LIST (count)
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Works as ``BUILD_TUPLE``, but creates a list.
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.. opcode:: BUILD_SET (count)
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Works as ``BUILD_TUPLE``, but creates a set.
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.. versionadded:: 2.7
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.. opcode:: BUILD_MAP (count)
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Pushes a new dictionary object onto the stack. The dictionary is pre-sized
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to hold *count* entries.
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.. opcode:: LOAD_ATTR (namei)
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Replaces TOS with ``getattr(TOS, co_names[namei])``.
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.. opcode:: COMPARE_OP (opname)
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Performs a Boolean operation. The operation name can be found in
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.. opcode:: IMPORT_NAME (namei)
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Imports the module ``co_names[namei]``. TOS and TOS1 are popped and provide
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the *fromlist* and *level* arguments of :func:`__import__`. The module
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object is pushed onto the stack. The current namespace is not affected: for
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a proper import statement, a subsequent ``STORE_FAST`` instruction modifies
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.. opcode:: IMPORT_FROM (namei)
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Loads the attribute ``co_names[namei]`` from the module found in TOS. The
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resulting object is pushed onto the stack, to be subsequently stored by a
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``STORE_FAST`` instruction.
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.. opcode:: JUMP_FORWARD (delta)
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Increments bytecode counter by *delta*.
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.. opcode:: POP_JUMP_IF_TRUE (target)
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If TOS is true, sets the bytecode counter to *target*. TOS is popped.
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.. opcode:: POP_JUMP_IF_FALSE (target)
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If TOS is false, sets the bytecode counter to *target*. TOS is popped.
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.. opcode:: JUMP_IF_TRUE_OR_POP (target)
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If TOS is true, sets the bytecode counter to *target* and leaves TOS on the
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stack. Otherwise (TOS is false), TOS is popped.
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.. opcode:: JUMP_IF_FALSE_OR_POP (target)
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If TOS is false, sets the bytecode counter to *target* and leaves TOS on the
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stack. Otherwise (TOS is true), TOS is popped.
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.. opcode:: JUMP_ABSOLUTE (target)
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Set bytecode counter to *target*.
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.. opcode:: FOR_ITER (delta)
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``TOS`` is an :term:`iterator`. Call its :meth:`!next` method. If this
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yields a new value, push it on the stack (leaving the iterator below it). If
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the iterator indicates it is exhausted ``TOS`` is popped, and the bytecode
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counter is incremented by *delta*.
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.. opcode:: LOAD_GLOBAL (namei)
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Loads the global named ``co_names[namei]`` onto the stack.
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.. opcode:: SETUP_LOOP (delta)
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Pushes a block for a loop onto the block stack. The block spans from the
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current instruction with a size of *delta* bytes.
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.. opcode:: SETUP_EXCEPT (delta)
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Pushes a try block from a try-except clause onto the block stack. *delta*
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points to the first except block.
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.. opcode:: SETUP_FINALLY (delta)
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Pushes a try block from a try-except clause onto the block stack. *delta*
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points to the finally block.
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.. opcode:: STORE_MAP ()
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Store a key and value pair in a dictionary. Pops the key and value while
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leaving the dictionary on the stack.
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.. opcode:: LOAD_FAST (var_num)
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Pushes a reference to the local ``co_varnames[var_num]`` onto the stack.
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.. opcode:: STORE_FAST (var_num)
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Stores TOS into the local ``co_varnames[var_num]``.
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.. opcode:: DELETE_FAST (var_num)
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Deletes local ``co_varnames[var_num]``.
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.. opcode:: LOAD_CLOSURE (i)
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Pushes a reference to the cell contained in slot *i* of the cell and free
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variable storage. The name of the variable is ``co_cellvars[i]`` if *i* is
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less than the length of *co_cellvars*. Otherwise it is ``co_freevars[i -
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.. opcode:: LOAD_DEREF (i)
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Loads the cell contained in slot *i* of the cell and free variable storage.
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Pushes a reference to the object the cell contains on the stack.
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.. opcode:: STORE_DEREF (i)
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Stores TOS into the cell contained in slot *i* of the cell and free variable
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.. opcode:: SET_LINENO (lineno)
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This opcode is obsolete.
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.. opcode:: RAISE_VARARGS (argc)
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Raises an exception. *argc* indicates the number of parameters to the raise
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statement, ranging from 0 to 3. The handler will find the traceback as TOS2,
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the parameter as TOS1, and the exception as TOS.
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.. opcode:: CALL_FUNCTION (argc)
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Calls a function. The low byte of *argc* indicates the number of positional
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parameters, the high byte the number of keyword parameters. On the stack, the
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opcode finds the keyword parameters first. For each keyword argument, the
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value is on top of the key. Below the keyword parameters, the positional
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parameters are on the stack, with the right-most parameter on top. Below the
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parameters, the function object to call is on the stack. Pops all function
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arguments, and the function itself off the stack, and pushes the return
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.. opcode:: MAKE_FUNCTION (argc)
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Pushes a new function object on the stack. TOS is the code associated with
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the function. The function object is defined to have *argc* default
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parameters, which are found below TOS.
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.. opcode:: MAKE_CLOSURE (argc)
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Creates a new function object, sets its *func_closure* slot, and pushes it on
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the stack. TOS is the code associated with the function, TOS1 the tuple
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containing cells for the closure's free variables. The function also has
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*argc* default parameters, which are found below the cells.
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.. opcode:: BUILD_SLICE (argc)
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.. index:: builtin: slice
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Pushes a slice object on the stack. *argc* must be 2 or 3. If it is 2,
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``slice(TOS1, TOS)`` is pushed; if it is 3, ``slice(TOS2, TOS1, TOS)`` is
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pushed. See the :func:`slice` built-in function for more information.
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.. opcode:: EXTENDED_ARG (ext)
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Prefixes any opcode which has an argument too big to fit into the default two
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bytes. *ext* holds two additional bytes which, taken together with the
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subsequent opcode's argument, comprise a four-byte argument, *ext* being the
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two most-significant bytes.
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.. opcode:: CALL_FUNCTION_VAR (argc)
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Calls a function. *argc* is interpreted as in :opcode:`CALL_FUNCTION`. The
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top element on the stack contains the variable argument list, followed by
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keyword and positional arguments.
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.. opcode:: CALL_FUNCTION_KW (argc)
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Calls a function. *argc* is interpreted as in :opcode:`CALL_FUNCTION`. The
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top element on the stack contains the keyword arguments dictionary, followed
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by explicit keyword and positional arguments.
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.. opcode:: CALL_FUNCTION_VAR_KW (argc)
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Calls a function. *argc* is interpreted as in :opcode:`CALL_FUNCTION`. The
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top element on the stack contains the keyword arguments dictionary, followed
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by the variable-arguments tuple, followed by explicit keyword and positional
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.. opcode:: HAVE_ARGUMENT ()
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This is not really an opcode. It identifies the dividing line between
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opcodes which don't take arguments ``< HAVE_ARGUMENT`` and those which do
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``>= HAVE_ARGUMENT``.
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python-2.7.12-docs-html/_sources/library/dis.txt
