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[3.6] bpo-26213: Document _UNPACK bytecodes and BUILD_MAP changes #440

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Mar 3, 2017
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[3.6] bpo-26213: Document _UNPACK bytecodes and BUILD_MAP changes #440

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55 changes: 53 additions & 2 deletions Doc/library/dis.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -772,8 +772,13 @@ All of the following opcodes use their arguments.

.. opcode:: BUILD_MAP (count)

Pushes a new dictionary object onto the stack. The dictionary is pre-sized
to hold *count* entries.
Pushes a new dictionary object onto the stack. Pops ``2 * count`` items
so that the dictionary holds *count* entries:
``{..., TOS3: TOS2, TOS1: TOS}``.

.. versionchanged:: 3.5
The dictionary is created from stack items instead of creating an
empty dictionary pre-sized to hold *count* items.


.. opcode:: BUILD_CONST_KEY_MAP (count)
Expand All @@ -793,6 +798,52 @@ All of the following opcodes use their arguments.
.. versionadded:: 3.6


.. opcode:: BUILD_TUPLE_UNPACK (count)

Pops *count* iterables from the stack, joins them in a single tuple,
and pushes the result. Implements iterable unpacking in tuple
displays ``(*x, *y, *z)``.

.. versionadded:: 3.5


.. opcode:: BUILD_LIST_UNPACK (count)

This is similar to :opcode:`BUILD_TUPLE_UNPACK`, but pushes a list
instead of tuple. Implements iterable unpacking in list
displays ``[*x, *y, *z]``.

.. versionadded:: 3.5


.. opcode:: BUILD_SET_UNPACK (count)

This is similar to :opcode:`BUILD_TUPLE_UNPACK`, but pushes a set
instead of tuple. Implements iterable unpacking in set
displays ``{*x, *y, *z}``.

.. versionadded:: 3.5


.. opcode:: BUILD_MAP_UNPACK (count)

Pops *count* mappings from the stack, merges them into a single dictionary,
and pushes the result. Implements dictionary unpacking in dictionary
displays ``{**x, **y, **z}``.

.. versionadded:: 3.5


.. opcode:: BUILD_MAP_UNPACK_WITH_CALL (oparg)

This is similar to :opcode:`BUILD_MAP_UNPACK`,
but is used for ``f(**x, **y, **z)`` call syntax. The lowest byte of
*oparg* is the count of mappings, the relative position of the
corresponding callable ``f`` is encoded in the second byte of *oparg*.

.. versionadded:: 3.5


.. opcode:: LOAD_ATTR (namei)

Replaces TOS with ``getattr(TOS, co_names[namei])``.
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