# SOME DESCRIPTIVE TITLE. # Copyright (C) 2001-2016, Python Software Foundation # This file is distributed under the same license as the Python package. # FIRST AUTHOR , YEAR. # #, fuzzy msgid "" msgstr "" "Project-Id-Version: Python 3.6\n" "Report-Msgid-Bugs-To: \n" "POT-Creation-Date: 2017-08-10 00:49+0200\n" "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n" "Last-Translator: FULL NAME \n" "Language-Team: LANGUAGE \n" "Language: fr\n" "MIME-Version: 1.0\n" "Content-Type: text/plain; charset=UTF-8\n" "Content-Transfer-Encoding: 8bit\n" #: ../Doc/howto/descriptor.rst:3 msgid "Descriptor HowTo Guide" msgstr "" #: ../Doc/howto/descriptor.rst:0 msgid "Author" msgstr "" #: ../Doc/howto/descriptor.rst:5 msgid "Raymond Hettinger" msgstr "" #: ../Doc/howto/descriptor.rst:0 msgid "Contact" msgstr "" #: ../Doc/howto/descriptor.rst:6 msgid "" msgstr "" #: ../Doc/howto/descriptor.rst:11 msgid "Abstract" msgstr "Résumé" #: ../Doc/howto/descriptor.rst:13 msgid "" "Defines descriptors, summarizes the protocol, and shows how descriptors are " "called. Examines a custom descriptor and several built-in python " "descriptors including functions, properties, static methods, and class " "methods. Shows how each works by giving a pure Python equivalent and a " "sample application." msgstr "" #: ../Doc/howto/descriptor.rst:18 msgid "" "Learning about descriptors not only provides access to a larger toolset, it " "creates a deeper understanding of how Python works and an appreciation for " "the elegance of its design." msgstr "" #: ../Doc/howto/descriptor.rst:24 msgid "Definition and Introduction" msgstr "" #: ../Doc/howto/descriptor.rst:26 msgid "" "In general, a descriptor is an object attribute with \"binding behavior\", " "one whose attribute access has been overridden by methods in the descriptor " "protocol. Those methods are :meth:`__get__`, :meth:`__set__`, and :meth:" "`__delete__`. If any of those methods are defined for an object, it is said " "to be a descriptor." msgstr "" #: ../Doc/howto/descriptor.rst:32 msgid "" "The default behavior for attribute access is to get, set, or delete the " "attribute from an object's dictionary. For instance, ``a.x`` has a lookup " "chain starting with ``a.__dict__['x']``, then ``type(a).__dict__['x']``, and " "continuing through the base classes of ``type(a)`` excluding metaclasses. If " "the looked-up value is an object defining one of the descriptor methods, " "then Python may override the default behavior and invoke the descriptor " "method instead. Where this occurs in the precedence chain depends on which " "descriptor methods were defined." msgstr "" #: ../Doc/howto/descriptor.rst:41 msgid "" "Descriptors are a powerful, general purpose protocol. They are the " "mechanism behind properties, methods, static methods, class methods, and :" "func:`super()`. They are used throughout Python itself to implement the new " "style classes introduced in version 2.2. Descriptors simplify the " "underlying C-code and offer a flexible set of new tools for everyday Python " "programs." msgstr "" #: ../Doc/howto/descriptor.rst:49 msgid "Descriptor Protocol" msgstr "" #: ../Doc/howto/descriptor.rst:51 msgid "``descr.__get__(self, obj, type=None) --> value``" msgstr "" #: ../Doc/howto/descriptor.rst:53 msgid "``descr.__set__(self, obj, value) --> None``" msgstr "" #: ../Doc/howto/descriptor.rst:55 msgid "``descr.__delete__(self, obj) --> None``" msgstr "" #: ../Doc/howto/descriptor.rst:57 msgid "" "That is all there is to it. Define any of these methods and an object is " "considered a descriptor and can override default behavior upon being looked " "up as an attribute." msgstr "" #: ../Doc/howto/descriptor.rst:61 msgid "" "If an object defines both :meth:`__get__` and :meth:`__set__`, it is " "considered a data descriptor. Descriptors that only define :meth:`__get__` " "are called non-data descriptors (they are typically used for methods but " "other uses are possible)." msgstr "" #: ../Doc/howto/descriptor.rst:66 msgid "" "Data and non-data descriptors differ in how overrides are calculated with " "respect to entries in an instance's dictionary. If an instance's dictionary " "has an entry with the same name as a data descriptor, the data descriptor " "takes precedence. If an instance's dictionary has an entry with the same " "name as a non-data descriptor, the dictionary entry takes precedence." msgstr "" #: ../Doc/howto/descriptor.rst:72 msgid "" "To make a read-only data descriptor, define both :meth:`__get__` and :meth:" "`__set__` with the :meth:`__set__` raising an :exc:`AttributeError` when " "called. Defining the :meth:`__set__` method with an exception raising " "placeholder is enough to make it a data descriptor." msgstr "" #: ../Doc/howto/descriptor.rst:79 msgid "Invoking Descriptors" msgstr "" #: ../Doc/howto/descriptor.rst:81 msgid "" "A descriptor can be called directly by its method name. For example, ``d." "__get__(obj)``." msgstr "" #: ../Doc/howto/descriptor.rst:84 msgid "" "Alternatively, it is more common for a descriptor to be invoked " "automatically upon attribute access. For example, ``obj.d`` looks up ``d`` " "in the dictionary of ``obj``. If ``d`` defines the method :meth:`__get__`, " "then ``d.__get__(obj)`` is invoked according to the precedence rules listed " "below." msgstr "" #: ../Doc/howto/descriptor.rst:89 msgid "" "The details of invocation depend on whether ``obj`` is an object or a class." msgstr "" #: ../Doc/howto/descriptor.rst:91 msgid "" "For objects, the machinery is in :meth:`object.__getattribute__` which " "transforms ``b.x`` into ``type(b).__dict__['x'].__get__(b, type(b))``. The " "implementation works through a precedence chain that gives data descriptors " "priority over instance variables, instance variables priority over non-data " "descriptors, and assigns lowest priority to :meth:`__getattr__` if provided. " "The full C implementation can be found in :c:func:" "`PyObject_GenericGetAttr()` in :source:`Objects/object.c`." msgstr "" #: ../Doc/howto/descriptor.rst:99 msgid "" "For classes, the machinery is in :meth:`type.__getattribute__` which " "transforms ``B.x`` into ``B.__dict__['x'].__get__(None, B)``. In pure " "Python, it looks like::" msgstr "" #: ../Doc/howto/descriptor.rst:110 msgid "The important points to remember are:" msgstr "" #: ../Doc/howto/descriptor.rst:112 msgid "descriptors are invoked by the :meth:`__getattribute__` method" msgstr "" #: ../Doc/howto/descriptor.rst:113 msgid "overriding :meth:`__getattribute__` prevents automatic descriptor calls" msgstr "" #: ../Doc/howto/descriptor.rst:114 msgid "" ":meth:`object.__getattribute__` and :meth:`type.__getattribute__` make " "different calls to :meth:`__get__`." msgstr "" #: ../Doc/howto/descriptor.rst:116 msgid "data descriptors always override instance dictionaries." msgstr "" #: ../Doc/howto/descriptor.rst:117 msgid "non-data descriptors may be overridden by instance dictionaries." msgstr "" #: ../Doc/howto/descriptor.rst:119 msgid "" "The object returned by ``super()`` also has a custom :meth:" "`__getattribute__` method for invoking descriptors. The call ``super(B, " "obj).m()`` searches ``obj.__class__.__mro__`` for the base class ``A`` " "immediately following ``B`` and then returns ``A.__dict__['m'].__get__(obj, " "B)``. If not a descriptor, ``m`` is returned unchanged. If not in the " "dictionary, ``m`` reverts to a search using :meth:`object.__getattribute__`." msgstr "" #: ../Doc/howto/descriptor.rst:126 msgid "" "The implementation details are in :c:func:`super_getattro()` in :source:" "`Objects/typeobject.c`. and a pure Python equivalent can be found in " "`Guido's Tutorial`_." msgstr "" #: ../Doc/howto/descriptor.rst:132 msgid "" "The details above show that the mechanism for descriptors is embedded in " "the :meth:`__getattribute__()` methods for :class:`object`, :class:`type`, " "and :func:`super`. Classes inherit this machinery when they derive from :" "class:`object` or if they have a meta-class providing similar functionality. " "Likewise, classes can turn-off descriptor invocation by overriding :meth:" "`__getattribute__()`." msgstr "" #: ../Doc/howto/descriptor.rst:141 msgid "Descriptor Example" msgstr "" #: ../Doc/howto/descriptor.rst:143 msgid "" "The following code creates a class whose objects are data descriptors which " "print a message for each get or set. Overriding :meth:`__getattribute__` is " "alternate approach that could do this for every attribute. However, this " "descriptor is useful for monitoring just a few chosen attributes::" msgstr "" #: ../Doc/howto/descriptor.rst:181 msgid "" "The protocol is simple and offers exciting possibilities. Several use cases " "are so common that they have been packaged into individual function calls. " "Properties, bound and unbound methods, static methods, and class methods are " "all based on the descriptor protocol." msgstr "" #: ../Doc/howto/descriptor.rst:188 msgid "Properties" msgstr "" #: ../Doc/howto/descriptor.rst:190 msgid "" "Calling :func:`property` is a succinct way of building a data descriptor " "that triggers function calls upon access to an attribute. Its signature is::" msgstr "" #: ../Doc/howto/descriptor.rst:195 msgid "" "The documentation shows a typical use to define a managed attribute ``x``::" msgstr "" #: ../Doc/howto/descriptor.rst:203 msgid "" "To see how :func:`property` is implemented in terms of the descriptor " "protocol, here is a pure Python equivalent::" msgstr "" #: ../Doc/howto/descriptor.rst:243 msgid "" "The :func:`property` builtin helps whenever a user interface has granted " "attribute access and then subsequent changes require the intervention of a " "method." msgstr "" #: ../Doc/howto/descriptor.rst:247 msgid "" "For instance, a spreadsheet class may grant access to a cell value through " "``Cell('b10').value``. Subsequent improvements to the program require the " "cell to be recalculated on every access; however, the programmer does not " "want to affect existing client code accessing the attribute directly. The " "solution is to wrap access to the value attribute in a property data " "descriptor::" msgstr "" #: ../Doc/howto/descriptor.rst:263 msgid "Functions and Methods" msgstr "" #: ../Doc/howto/descriptor.rst:265 msgid "" "Python's object oriented features are built upon a function based " "environment. Using non-data descriptors, the two are merged seamlessly." msgstr "" #: ../Doc/howto/descriptor.rst:268 msgid "" "Class dictionaries store methods as functions. In a class definition, " "methods are written using :keyword:`def` and :keyword:`lambda`, the usual " "tools for creating functions. The only difference from regular functions is " "that the first argument is reserved for the object instance. By Python " "convention, the instance reference is called *self* but may be called *this* " "or any other variable name." msgstr "" #: ../Doc/howto/descriptor.rst:275 msgid "" "To support method calls, functions include the :meth:`__get__` method for " "binding methods during attribute access. This means that all functions are " "non-data descriptors which return bound or unbound methods depending whether " "they are invoked from an object or a class. In pure python, it works like " "this::" msgstr "" #: ../Doc/howto/descriptor.rst:287 msgid "" "Running the interpreter shows how the function descriptor works in practice::" msgstr "" #: ../Doc/howto/descriptor.rst:301 msgid "" "The output suggests that bound and unbound methods are two different types. " "While they could have been implemented that way, the actual C implementation " "of :c:type:`PyMethod_Type` in :source:`Objects/classobject.c` is a single " "object with two different representations depending on whether the :attr:" "`im_self` field is set or is *NULL* (the C equivalent of ``None``)." msgstr "" #: ../Doc/howto/descriptor.rst:307 msgid "" "Likewise, the effects of calling a method object depend on the :attr:" "`im_self` field. If set (meaning bound), the original function (stored in " "the :attr:`im_func` field) is called as expected with the first argument set " "to the instance. If unbound, all of the arguments are passed unchanged to " "the original function. The actual C implementation of :func:" "`instancemethod_call()` is only slightly more complex in that it includes " "some type checking." msgstr "" #: ../Doc/howto/descriptor.rst:316 msgid "Static Methods and Class Methods" msgstr "" #: ../Doc/howto/descriptor.rst:318 msgid "" "Non-data descriptors provide a simple mechanism for variations on the usual " "patterns of binding functions into methods." msgstr "" #: ../Doc/howto/descriptor.rst:321 msgid "" "To recap, functions have a :meth:`__get__` method so that they can be " "converted to a method when accessed as attributes. The non-data descriptor " "transforms an ``obj.f(*args)`` call into ``f(obj, *args)``. Calling ``klass." "f(*args)`` becomes ``f(*args)``." msgstr "" #: ../Doc/howto/descriptor.rst:326 msgid "This chart summarizes the binding and its two most useful variants:" msgstr "" #: ../Doc/howto/descriptor.rst:329 msgid "Transformation" msgstr "" #: ../Doc/howto/descriptor.rst:329 msgid "Called from an Object" msgstr "" #: ../Doc/howto/descriptor.rst:329 msgid "Called from a Class" msgstr "" #: ../Doc/howto/descriptor.rst:332 msgid "function" msgstr "fonction" #: ../Doc/howto/descriptor.rst:332 msgid "f(obj, \\*args)" msgstr "" #: ../Doc/howto/descriptor.rst:332 ../Doc/howto/descriptor.rst:334 msgid "f(\\*args)" msgstr "" #: ../Doc/howto/descriptor.rst:334 msgid "staticmethod" msgstr "" #: ../Doc/howto/descriptor.rst:336 msgid "classmethod" msgstr "" #: ../Doc/howto/descriptor.rst:336 msgid "f(type(obj), \\*args)" msgstr "" #: ../Doc/howto/descriptor.rst:336 msgid "f(klass, \\*args)" msgstr "" #: ../Doc/howto/descriptor.rst:339 msgid "" "Static methods return the underlying function without changes. Calling " "either ``c.f`` or ``C.f`` is the equivalent of a direct lookup into ``object." "__getattribute__(c, \"f\")`` or ``object.__getattribute__(C, \"f\")``. As a " "result, the function becomes identically accessible from either an object or " "a class." msgstr "" #: ../Doc/howto/descriptor.rst:345 msgid "" "Good candidates for static methods are methods that do not reference the " "``self`` variable." msgstr "" #: ../Doc/howto/descriptor.rst:348 msgid "" "For instance, a statistics package may include a container class for " "experimental data. The class provides normal methods for computing the " "average, mean, median, and other descriptive statistics that depend on the " "data. However, there may be useful functions which are conceptually related " "but do not depend on the data. For instance, ``erf(x)`` is handy conversion " "routine that comes up in statistical work but does not directly depend on a " "particular dataset. It can be called either from an object or the class: " "``s.erf(1.5) --> .9332`` or ``Sample.erf(1.5) --> .9332``." msgstr "" #: ../Doc/howto/descriptor.rst:357 msgid "" "Since staticmethods return the underlying function with no changes, the " "example calls are unexciting::" msgstr "" #: ../Doc/howto/descriptor.rst:370 msgid "" "Using the non-data descriptor protocol, a pure Python version of :func:" "`staticmethod` would look like this::" msgstr "" #: ../Doc/howto/descriptor.rst:382 msgid "" "Unlike static methods, class methods prepend the class reference to the " "argument list before calling the function. This format is the same for " "whether the caller is an object or a class::" msgstr "" #: ../Doc/howto/descriptor.rst:397 msgid "" "This behavior is useful whenever the function only needs to have a class " "reference and does not care about any underlying data. One use for " "classmethods is to create alternate class constructors. In Python 2.3, the " "classmethod :func:`dict.fromkeys` creates a new dictionary from a list of " "keys. The pure Python equivalent is::" msgstr "" #: ../Doc/howto/descriptor.rst:413 msgid "Now a new dictionary of unique keys can be constructed like this::" msgstr "" #: ../Doc/howto/descriptor.rst:418 msgid "" "Using the non-data descriptor protocol, a pure Python version of :func:" "`classmethod` would look like this::" msgstr ""