Скачать или смотреть How to Save an Array of Objects in a File Using Python

Learn how to easily save and load an array of custom objects in Python, tackling common issues like serialization with JSON and Pickle.
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This video is based on the question https://stackoverflow.com/q/69425162/ asked by the user 'Faezeh Farajzade' ( https://stackoverflow.com/u/14156156/ ) and on the answer https://stackoverflow.com/a/69431293/ provided by the user 'Ali Nadirkhanloo' ( https://stackoverflow.com/u/12349121/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Save an Array of Objects in a File Using Python

Working with custom objects in Python can be quite rewarding, especially when developing complex applications. However, when it comes to saving these objects to a file, challenges can arise. In this post, we will explore how to effectively save an array of custom objects, as exemplified by the pesrson class. We'll discuss the common pitfalls and present solutions using both Pickle and databases.

Understanding the Problem

You may have encountered difficulties when trying to save instances of a custom class to a file. The specific errors typically encountered include:

JSON Serialization Error: "TypeError: Object of type person is not JSON serializable"

Pickle Serialization Error: "cannot pickle 'PySide2.QtWidgets.QFrame' object"

Both errors indicate that the objects you are trying to save cannot be serialized directly because of the complex components they contain.

The Example Class

Consider the following simplified structure of the pesrson class, which is intended to hold various GUI elements for display in a PyQt application:

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

Creating an Instance

You can create an instance of the pesrson class like this:

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

Now, let's address how to save an array of these objects.

Solution Approaches

1. Using Pickle

The Pickle module in Python provides a simple way to serialize and deserialize Python objects. However, since your objects include PyQt widgets, you’ll encounter issues because not all components can be pickled.

Steps to Use Pickle:

Remove Non-Serializable Attributes: Before pickling, remove or modify attributes that cannot be serialized, such as widgets.

Implement Pickling Methods: Define custom methods within your class to facilitate pickling.

Here’s a brief example of how to adjust your class for pickling:

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

Saving to a File:

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

Loading from a File:

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

2. Using a Database

If your needs extend beyond simple serialization and you're dealing with more extensive data, using a database may be a more robust solution.

Steps to Use a Database:

Choose a Database: SQLite is a lightweight option that integrates well with Python.

Define a Table: Create a table to store your object attributes.

Insert and Retrieve Data:

Use INSERT commands to store data.

Use SELECT queries to retrieve and reconstruct object instances.

Here’s how you might design your database logic:

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

Conclusion

Saving an array of custom objects in Python can be achieved either through serialization with Pickle or using a database for storage. Each method has its pros and cons depending on your specific use case.

Use Pickle for straightforward cases but be wary of non-serializable attributes.

Opt for a database when you're managing larger datasets or require more structured data access.

By understanding these techniques, you can effectively save and retrieve data within your Python applications, enhancing their functionality and user experience.

Feel free to reach out if you have any questions or need further clarification on any of these steps!