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...setattr" builtins. The present PEP suggests a new syntax to make such access easier, allowing the coder for example to write: x.('foo_%d' % n) += 1 z = y.('foo_%d' % n).('bar_%s' % s) instead of: attr_name = 'foo_%d' % n setattr(x, attr_name, getattr(x, attr_name) + 1) z = getattr(getattr(y, 'foo_%d' % n), 'bar_%s' % s) Rationale Dictionary access and indexing both have a friendly invocation syntax: instead of x.__getitem__(12) the coder can write x[12]. This also allows the use of subs...
...setattr__() would have no way to get to the instance's attributes. Second, __setattr__() cannot use "normal" syntax for setting instance attributes, e.g. "self.name = foo" because that would cause recursive calls to __setattr__(). __findattr__() is always called regardless of whether the attribute is in __dict__ or not, and a flag in the instance object prevents recursive calls to __findattr__(). This gives the class a chance to perform some action for every attribute access. And because it is...
...setattr__ has also been trapped for any particular purpose. If so, she must specifically call that method rather than assigning to the dictionary. There are many different reasons to overload __setattr__ so there is a decent potential for clashes. For instance object database implementations often overload setattr for an entirely unrelated purpose. The string-based switch statement forces all attribute handlers to be specified in one place in the code. They may then dispatch to task-specific met...
...setattr(obj, self._name, value) else: raise AttributeError("Attribute already set") def set(self, obj, value): setattr(obj, self._name, value) def __delete__(self, obj): delattr(obj, self._name) Note that unlike the original implementation, the private attribute name is stable since it uses the name of the descriptor, and therefore instances of class A are pickleable. Example: property namespaces Python's property type takes three function argumen...
...setattr functions might need to be modified to accommodate this new functionality. If all types used the PyObject_GenericSetAttr function to set attributes that would localize the update code somewhat. They don't however (which is not too surprising), so it seems that all getattrfunc and getattrofunc functions will have to be updated. In addition, this would place an absolute requirement on C extension module authors to call some function when an attribute changes value (PyObject_TrackUpdate?)...
...setattr(mc, k, newv) elif type(v) in (type, ClassType): bind_all(v, builtin_only, stoplist, verbose) def f(): pass try: f.func_code.code except AttributeError: # detect non-CPython environments bind_all = lambda *args, **kwds: 0 del f import sys bind_all(sys.modules[__name__]) # Optimizer, optimize thyself! Note the automatic detection of a non-CPython environment that does not have bytecodes [3]. In that situation, the bind functions wou...
...setattr__: sometimes attributes are not stored in self.__dict__ (for example when using __slots__ or properties, or when using a built-in base class). The same pattern as for __getattribute__ applies, where you call the base class __setattr__ to do the actual work. Here's an example: class C(object): def __setattr__(self, name, value): if hasattr(self, name): raise AttributeError, "attributes are write-once" object.__setattr__(se...
...setattr__: sometimes attributes are not stored in self.__dict__ (for example when using __slots__ or properties, or when using a built-in base class). The same pattern as for __getattribute__ applies, where you call the base class __setattr__ to do the actual work. Here's an example: class C(object): def __setattr__(self, name, value): if hasattr(self, name): raise AttributeError, "attributes are write-once" object.__setattr__(self, name, value) ...
...setattr(toclass, x, fromdict[x]) Listing 3 # The tricky part -- initializing objects from the configuration global # `Configuration' is the top level of the object tree we're going # to mung Configuration = Controls() copy_instance(Configuration, configuration) Configuration.servers = []; for server in configuration[`servers']: Newsite = Server() copy_instance(Newsite, server) Configuration.servers.append(Newsite) Newsite.users = []; for user in server['users']: Ne...
...setattr and delattr operations now map to getitem, setitem and delitem on the celldict. The type of <module>.__dict__ and globals() is probably the only backwards incompatibility. When a module is initialized, its __builtins__ is initialized from the __builtin__ module's __dict__, which is itself a celldict. For each cell in __builtins__, the new module's __dict__ adds a cell with a NULL objptr, whose cellptr points to the corresponding cell of __builtins__. Python pseudo-code (ignoring ...
...setattr(obj, k, v) listitems Optional, and new in this PEP. If this is not None, it should be an iterator (not a sequence!) yielding successive list items. These list items will be pickled, and appended to the object using either obj.append(item) or obj.extend(list_of_items). This is primarily used for list subclasses, but may be used by other classes as long as they have append() and extend() methods with the appropriate signature. (Whether append() or extend() is used depends on which pick...
...setattr(self._cls, attr, value) def __delitem__(self, attr): delattr(self._cls, attr) def extend(cls): return lambda: ClassNamespace(cls) class Example: pass class ExtendedExample(namespace=extend(Example)): a = 1 b = 2 c = 3 >>> Example.a, Example.b, Example.c (1, 2, 3) Rejected Design Options Calling __autodecorate__ from type.__init__ Calling the new hook automatically from type.__init__, would achieve most of the goals of this PEP. However, u...
...setattr(f, k, kwds[k]) return f return decorate @attrs(versionadded="2.2", author="Guido van Rossum") def mymethod(f): ... Enforce function argument and return types. Note that this copies the func_name attribute from the old to the new function. func_name was made writable in Python 2.4a3: def accepts(*types): def check_accepts(f): assert len(types) == f.func_code.co_argcount def new_f(*args, **kwds): for (a, t) in zip(args, types): ...
...setattr() now also accept Unicode objects for the attribute name, which are converted to strings using the default encoding before lookup. Multiplication on string and Unicode now does proper bounds checking; e.g. 'a' * 65536 * 65536 will raise ValueError, "repeated string is too long." Better error message when continue is found in try statement in a loop. Standard library and extensions array: reverse() method of array now works. buffer_info() now does ...
...setattro implementation, almost all built-in objects now place PyObject_GenericGetAttr and (if they have any writable attributes) PyObject_GenericSetAttr in their tp_getattro and tp_setattro slots. (Or, they can leave these NULL, and inherit them from the default base object, if they arrange for an explicit call to PyType_InitDict() for the type before the first instance is created.) In the simplest case, PyObject_GenericGetAttr() does exactly one dictionary lookup: it looks up the attribute n...
...setattr(), assignment via self, etc.). Still, some things like types of attributes will not be visible at runtime in Python 3.5 and earlier, but this looks like a reasonable limitation. There will be only limited support of isinstance() and issubclass() as discussed above (these will always fail with TypeError for subscripted generic protocols, since a reliable answer could not be given at runtime in this case). But together with other introspection tools this give a reasonable perspective for r...