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A class diagram exemplifying the singleton pattern.. In object-oriented programming, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance.
In Python, everything is an object, even classes. Classes, as objects, have a class, which is known as their metaclass. Python also supports multiple inheritance and mixins. The language supports extensive introspection of types and classes. Types can be read and compared—types are instances of type. The attributes of an object can be ...
The v object can have its eigenclass evaluated (allocated) as a consequence of adding singleton methods to v. According to the Ruby's introspection method named class, the class of every class (and of every eigenclass) is constantly the Class class (denoted by c in the diagram). Class, and Struct are the only classes that have classes as instances.
Concrete classes have to explicitly declare they implement the immutable interface. This may not be possible if the concrete class "belongs to" third-party code, for instance, if it is contained within a library. The object is not really immutable and hence not suitable for use in data structures relying on immutability like hash maps.
Any call to a class (static or constructor call), triggers the static constructor execution. Static constructors are thread safe and implement a singleton pattern. When used in a generic programming class, static constructors are called at every new generic instantiation one per type. [8]: 38 [4]: 111 Static variables are instantiated as well.
This means that there is no way to change those parts of the object state, even though other parts of the object may be changeable (weakly immutable). If all fields are immutable, then the object is immutable. If the whole object cannot be extended by another class, the object is called strongly immutable. [4]
Cython also facilitates wrapping independent C or C++ code into python-importable modules. Cython is written in Python and C and works on Windows, macOS, and Linux, producing C source files compatible with CPython 2.6, 2.7, and 3.3 and later versions. The Cython source code that Cython compiles (to C) can use both Python 2 and Python 3 syntax ...
Python makes a distinction between lists and tuples. Lists are written as [1, 2, 3], are mutable, and cannot be used as the keys of dictionaries (dictionary keys must be immutable in Python). Tuples, written as (1, 2, 3), are immutable and thus can be used as keys of dictionaries, provided all of the tuple's elements are immutable.