diff options
Diffstat (limited to 'Doc/reference')
| -rw-r--r-- | Doc/reference/compound_stmts.rst | 17 | ||||
| -rw-r--r-- | Doc/reference/datamodel.rst | 33 | ||||
| -rw-r--r-- | Doc/reference/import.rst | 20 |
3 files changed, 47 insertions, 23 deletions
diff --git a/Doc/reference/compound_stmts.rst b/Doc/reference/compound_stmts.rst index d0d0646..c25c767 100644 --- a/Doc/reference/compound_stmts.rst +++ b/Doc/reference/compound_stmts.rst @@ -493,14 +493,15 @@ case the parameter's default value is substituted. If a parameter has a default value, all following parameters up until the "``*``" must also have a default value --- this is a syntactic restriction that is not expressed by the grammar. -**Default parameter values are evaluated when the function definition is -executed.** This means that the expression is evaluated once, when the function -is defined, and that the same "pre-computed" value is used for each call. This -is especially important to understand when a default parameter is a mutable -object, such as a list or a dictionary: if the function modifies the object -(e.g. by appending an item to a list), the default value is in effect modified. -This is generally not what was intended. A way around this is to use ``None`` -as the default, and explicitly test for it in the body of the function, e.g.:: +**Default parameter values are evaluated from left to right when the function +definition is executed.** This means that the expression is evaluated once, when +the function is defined, and that the same "pre-computed" value is used for each +call. This is especially important to understand when a default parameter is a +mutable object, such as a list or a dictionary: if the function modifies the +object (e.g. by appending an item to a list), the default value is in effect +modified. This is generally not what was intended. A way around this is to use +``None`` as the default, and explicitly test for it in the body of the function, +e.g.:: def whats_on_the_telly(penguin=None): if penguin is None: diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst index f8e9280..a88d562 100644 --- a/Doc/reference/datamodel.rst +++ b/Doc/reference/datamodel.rst @@ -934,6 +934,20 @@ Internal types frame). A debugger can implement a Jump command (aka Set Next Statement) by writing to f_lineno. + Frame objects support one method: + + .. method:: frame.clear() + + This method clears all references to local variables held by the + frame. Also, if the frame belonged to a generator, the generator + is finalized. This helps break reference cycles involving frame + objects (for example when catching an exception and storing its + traceback for later use). + + :exc:`RuntimeError` is raised if the frame is currently executing. + + .. versionadded:: 3.4 + Traceback objects .. index:: object: traceback @@ -1120,12 +1134,10 @@ Basic customization ``sys.last_traceback`` keeps the stack frame alive). The first situation can only be remedied by explicitly breaking the cycles; the latter two situations can be resolved by storing ``None`` in ``sys.last_traceback``. - Circular references which are garbage are detected when the option cycle - detector is enabled (it's on by default), but can only be cleaned up if - there are no Python- level :meth:`__del__` methods involved. Refer to the - documentation for the :mod:`gc` module for more information about how - :meth:`__del__` methods are handled by the cycle detector, particularly - the description of the ``garbage`` value. + Circular references which are garbage are detected and cleaned up when + the cyclic garbage collector is enabled (it's on by default). Refer to the + documentation for the :mod:`gc` module for more information about this + topic. .. warning:: @@ -1828,6 +1840,15 @@ through the container; for mappings, :meth:`__iter__` should be the same as considered to be false in a Boolean context. +.. method:: object.__length_hint__(self) + + Called to implement :func:`operator.length_hint`. Should return an estimated + length for the object (which may be greater or less than the actual length). + The length must be an integer ``>=`` 0. This method is purely an + optimization and is never required for correctness. + + .. versionadded:: 3.4 + .. note:: Slicing is done exclusively with the following three methods. A call like :: diff --git a/Doc/reference/import.rst b/Doc/reference/import.rst index eb497a1..b587fc9 100644 --- a/Doc/reference/import.rst +++ b/Doc/reference/import.rst @@ -373,16 +373,18 @@ Loaders must satisfy the following requirements: * The ``__loader__`` attribute must be set to the loader object that loaded the module. This is mostly for introspection and reloading, but can be used for additional loader-specific functionality, for example getting - data associated with a loader. + data associated with a loader. If the attribute is missing or set to ``None`` + then the import machinery will automatically set it **after** the module has + been imported. - * The module's ``__package__`` attribute should be set. Its value must be a + * The module's ``__package__`` attribute must be set. Its value must be a string, but it can be the same value as its ``__name__``. If the attribute is set to ``None`` or is missing, the import system will fill it in with a - more appropriate value. When the module is a package, its ``__package__`` - value should be set to its ``__name__``. When the module is not a package, - ``__package__`` should be set to the empty string for top-level modules, or - for submodules, to the parent package's name. See :pep:`366` for further - details. + more appropriate value **after** the module has been imported. + When the module is a package, its ``__package__`` value should be set to its + ``__name__``. When the module is not a package, ``__package__`` should be + set to the empty string for top-level modules, or for submodules, to the + parent package's name. See :pep:`366` for further details. This attribute is used instead of ``__name__`` to calculate explicit relative imports for main modules, as defined in :pep:`366`. @@ -425,8 +427,8 @@ Here are the exact rules used: * If the module has a ``__file__`` attribute, this is used as part of the module's repr. - * If the module has no ``__file__`` but does have a ``__loader__``, then the - loader's repr is used as part of the module's repr. + * If the module has no ``__file__`` but does have a ``__loader__`` that is not + ``None``, then the loader's repr is used as part of the module's repr. * Otherwise, just use the module's ``__name__`` in the repr. |