Скачать или смотреть Understanding the missing positional argument Error in Python Decorators

Learn how to resolve the `missing positional argument` error in Python decorators and understand the correct implementation of decorators.
---
This video is based on the question https://stackoverflow.com/q/64778091/ asked by the user 'SAHABAT LR' ( https://stackoverflow.com/u/14268367/ ) and on the answer https://stackoverflow.com/a/64778112/ provided by the user 'Random Davis' ( https://stackoverflow.com/u/6273251/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: missing positional argument on decorator

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Tackling the missing positional argument Error in Python Decorators

If you've encountered an error message while compiling your Python project that reads "TypeError: decorator() missing 1 required positional argument: 'func'", you're not alone. This common issue arises when using decorators incorrectly, particularly when the function arguments are misconfigured. In this post, we’ll delve into the problem, explain the underlying concepts of decorators, and illustrate how to fix the issue step-by-step.

Understanding Decorators in Python

Decorators are a powerful feature in Python that allows you to modify the behavior of a function or a method. They essentially wrap a function, allowing you to add functionality before or after the execution of the wrapped function without changing its code. Here’s a basic structure of a decorator:

[[See Video to Reveal this Text or Code Snippet]]

In this structure, func is the positional argument passed to the decorator.

The Problem: Missing Positional Argument

In the case that prompted this discussion, the decorator was defined as follows:

[[See Video to Reveal this Text or Code Snippet]]

This version incorrectly expects two arguments, self and func. The self is unnecessary in the context of a decorator because it is typically used in class methods. Consequently, this is what leads to the missing positional argument error when you try to decorate a function.

Error Breakdown:

Error Message: TypeError: decorator() missing 1 required positional argument: 'func'

Cause: The decorator expects a second argument, func, which it does not receive due to incorrect usage.

The Solution: Correcting the Decorator Definition

Step 1: Adjusting the Decorator Definition

You need to define your decorator without the self parameter. Change your function definition from:

[[See Video to Reveal this Text or Code Snippet]]

to:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Utilizing the Decorator

After fixing the definition, ensure your functions correctly utilize the decorator:

[[See Video to Reveal this Text or Code Snippet]]

Notice that self is no longer included in the decorator signature.

Step 3: Review and Refactor the Usage of Self

If you're using this decorator in a class context, ensure that any necessary functionality is handled properly without relying on self in the decorator. If your class methods require access to instance variables or methods, you can manage that within the actual method, not the decorator itself.

Example Implementation

Here is the corrected version of the decorator and the usage in the selectTransaction method:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Understanding how to construct and use decorators correctly is crucial for Python developers. By eliminating unnecessary parameters like self in decorators and ensuring proper decorator syntax, you can avoid the frustrating missing positional argument error. We hope this guide has clarified the essentials of decorators for you. Happy coding!