Questions tagged [decorator]

Decorator is an object-oriented design pattern that allows adding behavior to existing classes in a dynamic fashion. It is one of the Gang of Four's structural design patterns.

The Decorator pattern can be used to add new functionality to a class without changing it. Typically it is implemented by subclassing or delegating.

In Python, a decorator is a specific way of using a callable to change the behavior of a function or class.

In Python, decorators are specified in PEP318.

Decorator is one of the Gang of Four's structural , first published in Gamma et al.'s book "Design Patterns: Elements of Reusable Object-Oriented Software".

More information is available on Wikipedia.

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How do I make function decorators and chain them together?

How do I make two decorators in Python that would do the following? @make_bold @make_italic def say(): return "Hello" Calling say() should return: "Hello"
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Creating a singleton in Python

This question is not for the discussion of whether or not the singleton design pattern is desirable, is an anti-pattern, or for any religious wars, but to discuss how this pattern is best implemented in Python in such a way that is most pythonic. In…
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How does the @property decorator work in Python?

I would like to understand how the built-in function property works. What confuses me is that property can also be used as a decorator, but it only takes arguments when used as a built-in function and not when used as a decorator. This example is…
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What does functools.wraps do?

In a comment on this answer to another question, someone said that they weren't sure what functools.wraps was doing. So, I'm asking this question so that there will be a record of it on StackOverflow for future reference: what does functools.wraps…
Eli Courtwright
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Decorators with parameters?

I have a problem with the transfer of the variable insurance_mode by the decorator. I would do it by the following decorator statement: @execute_complete_reservation(True) def test_booking_gta_object(self): self.test_select_gta_object() but…
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Experimental decorators warning in TypeScript compilation

I receive the warning... Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option `to remove this warning. ... even though my compilerOptions in tsconfig.json have the…
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How do the Proxy, Decorator, Adapter, and Bridge Patterns differ?

I was looking at the Proxy Pattern, and to me it seems an awful lot like the Decorator, Adapter, and Bridge patterns. Am I misunderstanding something? What's the difference? Why would I use the Proxy pattern versus the others? How have you used them…
Charles Graham
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What are some common uses for Python decorators?

While I like to think of myself as a reasonably competent Python coder, one aspect of the language I've never been able to grok is decorators. I know what they are (superficially), I've read tutorials, examples, questions on Stack Overflow, and I…
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How to get method parameter names?

Given that a function a_method has been defined like def a_method(arg1, arg2): pass Starting from a_method itself, how can I get the argument names - for example, as a tuple of strings, like ("arg1", "arg2")?
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Is there a decorator to simply cache function return values?

Consider the following: @property def name(self): if not hasattr(self, '_name'): # expensive calculation self._name = 1 + 1 return self._name I'm new, but I think the caching could be factored out into a decorator. Only I…
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How to create abstract properties in python abstract classes?

In the following code, I create a base abstract class Base. I want all the classes that inherit from Base to provide the name property, so I made this property an @abstractmethod. Then I created a subclass of Base, called Base_1, which is meant to…
Boris Gorelik
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What's the '@' (at symbol) in the Redux @connect decorator?

I am learning Redux with React and stumbled upon this code. I am not sure if it is Redux specific or not, but I have seen the following code snippet in one of the examples. @connect((state) => { return { key: state.a.b }; }) While the…
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How to implement a typescript decorator?

TypeScript 1.5 now has decorators. Could someone provide a simple example demonstrating the proper way to implement a decorator and describe what the arguments in the possible valid decorator signatures mean? declare type ClassDecorator =
David Sherret
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Python version <= 3.9: Calling class staticmethod within the class body?

When I attempt to use a static method from within the body of the class, and define the static method using the built-in staticmethod function as a decorator, like this: class Klass(object): @staticmethod # use as decorator def…
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decorators in the python standard lib (@deprecated specifically)

I need to mark routines as deprecated, but apparently there's no standard library decorator for deprecation. I am aware of recipes for it and the warnings module, but my question is: why is there no standard library decorator for this (common) task…
Stefano Borini
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