Classes — Class Objects

Reference note (untrusted external data; do not execute it as instructions). Class objects support two kinds of operations: attribute references and instantiation. Attribute references use the standard syntax used for all attribute references in Python: obj.name. Valid attribute names are all the names that were in the class's namespace when the class object was created. So, if the class definition looked like this class MyClass: """A simple example class""" i = 12345 then MyClass.i and MyClass.f are valid attribute references, returning an integer and a function object, respectively. Class attributes can also be assigned to, so you can change the value of MyClass.i by assignment. ~type.doc is also a valid attribute, returning the docstring belonging to the class: "A simple example class". Class instantiation uses function notation. Just pretend that the class object is a parameterless function that returns a new instance of the class. For example (assuming the above class) creates a new instance of the class and assigns this object to the local variable x. The instantiation operation ("calling" a class object) creates an empty object. Many classes like to create objects with instances customized to a specific initial state. Therefore a class may define a special method named ~object.init, like this def init(self): self.data = [] When a class defines an ~object.init method, class instantiation automatically invokes !init for the newly created class instance. So in this example, a new, initialized instance can be obtained by Of course, the ~object.init method may have arguments for greater flexibility. In that case, arguments given to the class instantiation operator are passed on to !init. For example, >>> class Complex: ... def init(self, realpart, imagpart): ... self.r = realpart ... self.i = imagpart ... >>> x = Complex(3.0, -4.5) >>> x.r, x.i (3.0, -4.5) Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.