three.

.. opcode:: ROT_FOUR

Lifts second, third and forth stack items one position up, moves top down

to position four.

.. versionadded:: 3.8

.. opcode:: DUP_TOP

Duplicates the reference on top of the stack.

is terminated with :opcode:`POP_TOP`.

.. 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 :opcode:`FOR_ITER` instruction).

.. opcode:: SET_ADD (i)

Calls ``set.add(TOS1[-i], TOS)``. Used to implement set comprehensions.

.. 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.

blocks, denoting :keyword:`try` statements, and such.

.. opcode:: POP_EXCEPT

popped values are used to restore the exception state.

.. opcode:: POP_FINALLY (preserve_tos)

Cleans up the value stack and the block stack. If *preserve_tos* is not

``0`` TOS first is popped from the stack and pushed on the stack after

perfoming other stack operations:

* If TOS is ``NULL`` or an integer (pushed by :opcode:`BEGIN_FINALLY`

or :opcode:`CALL_FINALLY`) it is popped from the stack.

* If TOS is an exception type (pushed when an exception has been raised)

6 values are popped from the stack, the last three popped values are

used to restore the exception state. An exception handler block is

removed from the block stack.

It is similar to :opcode:`END_FINALLY`, but doesn't change the bytecode

counter nor raise an exception. Used for implementing :keyword:`break`

and :keyword:`return` in the :keyword:`finally` block.

.. versionadded:: 3.8

.. opcode:: BEGIN_FINALLY

Pushes ``NULL`` onto the stack for using it in :opcode:`END_FINALLY`,

:opcode:`POP_FINALLY`, :opcode:`WITH_CLEANUP_START` and

:opcode:`WITH_CLEANUP_FINISH`. Starts the :keyword:`finally` block.

.. versionadded:: 3.8

.. 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.

exception has to be re-raised or execution has to be continued depending on

the value of TOS.

* If TOS is ``NULL`` (pushed by :opcode:`BEGIN_FINALLY`) continue from

the next instruction. TOS is popped.

* If TOS is an integer (pushed by :opcode:`CALL_FINALLY`), sets the

bytecode counter to TOS. TOS is popped.

* If TOS is an exception type (pushed when an exception has been raised)

6 values are popped from the stack, the first three popped values are

used to re-raise the exception and the last three popped values are used

to restore the exception state. An exception handler block is removed

from the block stack.

.. opcode:: LOAD_BUILD_CLASS

This opcode performs several operations before a with block starts. First,

it loads :meth:`~object.__exit__` from the context manager and pushes it onto

the stack for later use by :opcode:`WITH_CLEANUP`. Then,

the stack for later use by :opcode:`WITH_CLEANUP_START`. Then,

:meth:`~object.__enter__` is called, and a finally block pointing to *delta*

is pushed. Finally, the result of calling the enter method is pushed onto

is pushed. Finally, the result of calling the ``__enter__()`` method is pushed onto

the stack. The next opcode will either ignore it (:opcode:`POP_TOP`), or

store it in (a) variable(s) (:opcode:`STORE_FAST`, :opcode:`STORE_NAME`, or

:opcode:`UNPACK_SEQUENCE`).

.. opcode:: WITH_CLEANUP_START

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:

Starts cleaning up the stack when a :keyword:`with` statement block exits.

* SECOND = ``None``

* (SECOND, THIRD) = (``WHY_{RETURN,CONTINUE}``), retval

* SECOND = ``WHY_*``; no retval below it

* (SECOND, THIRD, FOURTH) = exc_info()

At the top of the stack are either ``NULL`` (pushed by

:opcode:`BEGIN_FINALLY`) or 6 values pushed if an exception has been

raised in the with block. Below is the context manager's

:meth:`~object.__exit__` or :meth:`~object.__aexit__` bound method.

In the last case, ``TOS(SECOND, THIRD, FOURTH)`` is called, otherwise

``TOS(None, None, None)``. Pushes SECOND and result of the call

to the stack.

If TOS is ``NULL``, calls ``SECOND(None, None, None)``,

removes the function from the stack, leaving TOS, and pushes ``None``

to the stack. Otherwise calls ``SEVENTH(TOP, SECOND, THIRD)``,

shifts the bottom 3 values of the stack down, replaces the empty spot

with ``NULL`` and pushes TOS. Finally pushes the result of the call.

.. opcode:: WITH_CLEANUP_FINISH

Pops exception type and result of 'exit' function call from the stack.

Finishes cleaning up the stack when a :keyword:`with` statement block exits.

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 :opcode:`END_FINALLY` from re-raising the

exception. (But non-local gotos will still be resumed.)

TOS is result of ``__exit__()`` or ``__aexit__()`` function call pushed

by :opcode:`WITH_CLEANUP_START`. SECOND is ``None`` or an exception type

(pushed when an exception has been raised).

.. XXX explain the WHY stuff!

Pops two values from the stack. If SECOND is not None and TOS is true

unwinds the EXCEPT_HANDLER block which was created when the exception

was caught and pushes ``NULL`` to the stack.

All of the following opcodes use their arguments.

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_FINALLY (delta)

.. opcode:: SETUP_EXCEPT (delta)

Pushes a try block from a try-finally or try-except clause onto the block

stack. *delta* points to the finally block or the first except block.

Pushes a try block from a try-except clause onto the block stack. *delta*

points to the first except block.

.. opcode:: CALL_FINALLY (delta)

.. opcode:: SETUP_FINALLY (delta)

Pushes the address of the next instruction onto the stack and increments

bytecode counter by *delta*. Used for calling the finally block as a

"subroutine".

Pushes a try block from a try-except clause onto the block stack. *delta*

points to the finally block.

.. versionadded:: 3.8

.. opcode:: LOAD_FAST (var_num)