`dis` — Disassembler for Python bytecode¶

Source code: Lib/dis.py

The dis module supports the analysis of CPython bytecode by disassembling it. The CPython bytecode which this module takes as an input is defined in the file Include/opcode.h and used by the compiler and the interpreter.

CPython implementation detail: Bytecode is an implementation detail of the CPython interpreter. No guarantees are made that bytecode will not be added, removed, or changed between versions of Python. Use of this module should not be considered to work across Python VMs or Python releases.

Changed in version 3.6: Use 2 bytes for each instruction. Previously the number of bytes varied by instruction.

Changed in version 3.10: The argument of jump, exception handling and loop instructions is now the instruction offset rather than the byte offset.

Changed in version 3.11: Some instructions are accompanied by one or more inline cache entries, which take the form of CACHE instructions. These instructions are hidden by default, but can be shown by passing show_caches=True to any dis utility. Furthermore, the interpreter now adapts the bytecode to specialize it for different runtime conditions. The adaptive bytecode can be shown by passing adaptive=True.

Changed in version 3.12: The argument of a jump is the offset of the target instruction relative to the instruction that appears immediately after the jump instruction’s CACHE entries.

As a consequence, the presence of the CACHE instructions is transparent for forward jumps but needs to be taken into account when reasoning about backward jumps.

Changed in version 3.13: The output shows logical labels rather than instruction offsets for jump targets and exception handlers. The -O command line option and the show_offsets argument were added.

Changed in version 3.14: The -P command-line option and the show_positions argument were added.

The -S command-line option is added.

Example: Given the function myfunc():

def myfunc(alist):
    return len(alist)

the following command can be used to display the disassembly of myfunc():

>>> dis.dis(myfunc)
  2           RESUME                   0

  3           LOAD_GLOBAL              1 (len + NULL)
              LOAD_FAST_BORROW         0 (alist)
              CALL                     1
              RETURN_VALUE

(The “2” is a line number).

Command-line interface¶

The dis module can be invoked as a script from the command line:

python -m dis [-h] [-C] [-O] [-P] [-S] [infile]

The following options are accepted:

-h, --help¶: Display usage and exit.

-C, --show-caches¶: Show inline caches.

Added in version 3.13.

-O, --show-offsets¶: Show offsets of instructions.

Added in version 3.13.

-P, --show-positions¶: Show positions of instructions in the source code.

Added in version 3.14.

-S, --specialized¶: Show specialized bytecode.

Added in version 3.14.

If infile is specified, its disassembled code will be written to stdout. Otherwise, disassembly is performed on compiled source code received from stdin.

Bytecode analysis¶

Added in version 3.4.

The bytecode analysis API allows pieces of Python code to be wrapped in a Bytecode object that provides easy access to details of the compiled code.

class dis.Bytecode(x, *, first_line=None, current_offset=None, show_caches=False, adaptive=False, show_offsets=False, show_positions=False)¶

Analyse the bytecode corresponding to a function, generator, asynchronous generator, coroutine, method, string of source code, or a code object (as returned by compile()).

This is a convenience wrapper around many of the functions listed below, most notably get_instructions(), as iterating over a Bytecode instance yields the bytecode operations as Instruction instances.

If first_line is not None, it indicates the line number that should be reported for the first source line in the disassembled code. Otherwise, the source line information (if any) is taken directly from the disassembled code object.

If current_offset is not None, it refers to an instruction offset in the disassembled code. Setting this means dis() will display a “current instruction” marker against the specified opcode.

If show_caches is True, dis() will display inline cache entries used by the interpreter to specialize the bytecode.

If adaptive is True, dis() will display specialized bytecode that may be different from the original bytecode.

If show_offsets is True, dis() will include instruction offsets in the output.

If show_positions is True, dis() will include instruction source code positions in the output.

classmethod from_traceback(tb, *, show_caches=False)¶: Construct a Bytecode instance from the given traceback, setting current_offset to the instruction responsible for the exception.

codeobj¶: The compiled code object.

first_line¶: The first source line of the code object (if available)

dis()¶: Return a formatted view of the bytecode operations (the same as printed by dis.dis(), but returned as a multi-line string).

info()¶: Return a formatted multi-line string with detailed information about the code object, like code_info().

Changed in version 3.7: This can now handle coroutine and asynchronous generator objects.

Changed in version 3.11: Added the show_caches and adaptive parameters.

Changed in version 3.13: Added the show_offsets parameter

Changed in version 3.14: Added the show_positions parameter.

Example:

>>> bytecode = dis.Bytecode(myfunc)
>>> for instr in bytecode:
...     print(instr.opname)
...
RESUME
LOAD_GLOBAL
LOAD_FAST_BORROW
CALL
RETURN_VALUE

Analysis functions¶

The dis module also defines the following analysis functions that convert the input directly to the desired output. They can be useful if only a single operation is being performed, so the intermediate analysis object isn’t useful:

dis.code_info(x)¶

Return a formatted multi-line string with detailed code object information for the supplied function, generator, asynchronous generator, coroutine, method, source code string or code object.

Note that the exact contents of code info strings are highly implementation dependent and they may change arbitrarily across Python VMs or Python releases.

Added in version 3.2.

Changed in version 3.7: This can now handle coroutine and asynchronous generator objects.

dis.show_code(x, *, file=None)¶

Print detailed code object information for the supplied function, method, source code string or code object to file (or sys.stdout if file is not specified).

This is a convenient shorthand for print(code_info(x), file=file), intended for interactive exploration at the interpreter prompt.

Added in version 3.2.

Changed in version 3.4: Added file parameter.

dis.dis(x=None, *, file=None, depth=None, show_caches=False, adaptive=False, show_offsets=False, show_positions=False)¶

Disassemble the x object. x can denote either a module, a class, a method, a function, a generator, an asynchronous generator, a coroutine, a code object, a string of source code or a byte sequence of raw bytecode. For a module, it disassembles all functions. For a class, it disassembles all methods (including class and static methods). For a code object or sequence of raw bytecode, it prints one line per bytecode instruction. It also recursively disassembles nested code objects. These can include generator expressions, nested functions, the bodies of nested classes, and the code objects used for annotation scopes. Strings are first compiled to code objects with the compile() built-in function before being disassembled. If no object is provided, this function disassembles the last traceback.

The disassembly is written as text to the supplied file argument if provided and to sys.stdout otherwise.

The maximal depth of recursion is limited by depth unless it is None. depth=0 means no recursion.

If show_caches is True, this function will display inline cache entries used by the interpreter to specialize the bytecode.

If adaptive is True, this function will display specialized bytecode that may be different from the original bytecode.

Changed in version 3.4: Added file parameter.

Changed in version 3.7: Implemented recursive disassembling and added depth parameter.

Changed in version 3.7: This can now handle coroutine and asynchronous generator objects.

Changed in version 3.11: Added the show_caches and adaptive parameters.

Changed in version 3.13: Added the show_offsets parameter.

Changed in version 3.14: Added the show_positions parameter.

dis.distb(tb=None, *, file=None, show_caches=False, adaptive=False, show_offset=False, show_positions=False)¶

Disassemble the top-of-stack function of a traceback, using the last traceback if none was passed. The instruction causing the exception is indicated.

The disassembly is written as text to the supplied file argument if provided and to sys.stdout otherwise.

Changed in version 3.4: Added file parameter.

Changed in version 3.11: Added the show_caches and adaptive parameters.

Changed in version 3.13: Added the show_offsets parameter.

Changed in version 3.14: Added the show_positions parameter.

dis.disassemble(code, lasti=-1, *, file=None, show_caches=False, adaptive=False, show_offsets=False, show_positions=False)¶

dis.disco(code, lasti=-1, *, file=None, show_caches=False, adaptive=False, show_offsets=False, show_positions=False)¶

Disassemble a code object, indicating the last instruction if lasti was provided. The output is divided in the following columns:

the source code location of the instruction. Complete location information is shown if show_positions is true. Otherwise (the default) only the line number is displayed.
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.

The disassembly is written as text to the supplied file argument if provided and to sys.stdout otherwise.

Changed in version 3.4: Added file parameter.

Changed in version 3.11: Added the show_caches and adaptive parameters.

Changed in version 3.13: Added the show_offsets parameter.

Changed in version 3.14: Added the show_positions parameter.

dis.get_instructions(x, *, first_line=None, show_caches=False, adaptive=False)¶

Return an iterator over the instructions in the supplied function, method, source code string or code object.

The iterator generates a series of Instruction named tuples giving the details of each operation in the supplied code.

The

dis — Disassembler for Python bytecode¶

Command-line interface¶

Bytecode analysis¶

Analysis functions¶

`dis` — Disassembler for Python bytecode¶