PDF Guide to: Learning Python Decorators

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Here the index function returns the dictionary, which for Flask is an invalid response type. Here is the complete application, including the implementation of this decorator:.

#44 Python Tutorial for Beginners - Decorators

The wrapped function simply invokes the original function, called f in this context, and then checks if the return value is a dictionary or list, in which case it calls jsonify , effectively intercepting and fixing the return value before it is returned to the framework. Note: As of Flask version 1. So while the above decorator is not needed anymore, it is still a good example of building filters using the decorator pattern.

Yet another useful technique that can be implemented with decorators is to perform any kind of validation before the decorated function is allowed to run. A very common example in a web application is to authenticate the user. If the token header isn't present, or if it is present but the token does not match, then the abort function from Flask is used to generate a response and halt the request.

Otherwise the request is allowed to go through by invoking the decorated function. This is called decorator chaining. Chaining decorators is a tricky topic so I'm going to dedicate some time to it in a future article. For those of you working with Flask, assume that almost always the app.

So far I have only shown you decorators that do not take any arguments themselves, the arguments always go to the decorated function. I have done this on purpose, because decorators that accept arguments of their own in addition to those that are passed through to the decorated function are more complex to write.


Python Decorator Tutorial : How To Use Decorators In Python

This is going to be the topic of the next articles, so make sure you familiarize yourself with the concepts I covered in this and the previous article and be ready for another jump in complexity in the next installment! Hello, and thank you for visiting my blog! If you enjoyed this article, please consider supporting my work on this blog on Patreon! My Kickstarter project was a big success! Thank you to everyone who contributed to it!

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Toggle navigation miguelgrinberg. Simple Decorators Review Before we delve into new territory, let's review how the simple decorators from Part I work. Decorators That Replace The Decorated Function The more advanced decorators that I'm going to show you next are not going to return the same function like the one above, they are going to return a different function, and this is going to enable an array of very cool tricks the simpler decorators cannot do.

Example 2: Altering the Return Value of a Function Another very common task decorators are good for is to perform a conversion on the return value of the decorated function. If the order was different in the example above, the output would have been different. Decorating Methods In Python, methods are functions that expect their first parameter to be a reference to the current object. We can build decorators for methods the same way, while taking self into consideration in the wrapper function. A much better approach would be to make our decorator useful for functions and methods alike.

It took a bit more work in this case. Decorators expect to receive a function as an argument, that is why we will have to build a function that takes those extra arguments and generate our decorator on the fly.

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In the example above tags, is our decorator generator. Debugging decorated functions At the end of the day decorators are just wrapping our functions, in case of debugging that can be problematic since the wrapper function does not carry the name, module and docstring of the original function.

Decorators That Replace The Decorated Function

Based on the example above if we do:. Output: func wrapper The output was expected to be get text yet, the attributes name , doc , and module of get text got overridden by those of the wrapper func wrapper. Functools to the rescue. Skip to main content. Android Development. Books to Read for Programmers. BSD operating system. Cloud Development. Computational Genomics.

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Python Decorator Tutorial | Introduction To Decorator In Python | Edureka

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