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Learn how to display the exact `line number` of errors when validating JSON data with Python and JSON schema.
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How to Print the Specific Line Number of Errors in a JSON File Using Python

Validating JSON data against a schema can often lead to frustrating moments, especially when errors arise. A common issue developers face is wanting to know exactly where in the JSON file a problem occurs. If you're using Python and JSON Schema to validate your data, you may find yourself asking, "How can I print the specific line number of a JSON file error?" This guide addresses that question and offers a detailed explanation on how to achieve this.

Understanding the Problem

When you load a JSON file in Python and validate it, the JSON content is parsed into a data structure. At this point, the line number information from the original JSON file is no longer accessible. As a result, even if you catch errors using JSON Schema validation, the error messages alone don’t indicate where the problem is found in the original file.

Imagine receiving the message:

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

You might wonder, "On which line does this error occur?" Unfortunately, without additional tools, the answer might remain elusive.

The Solution: Line Number Mapping

To effectively include line numbers in your error messages, you can implement a specific method during JSON loading. Here’s how to do it step by step:

1. Use a Custom JSON Decoder

Instead of using Python’s built-in JSON decoder, you can create or utilize a custom decoder that captures line numbers as it parses the JSON file. This decoder should maintain a mapping of line numbers related to each JSON element.

Example of JSON Structure

Consider this sample JSON:

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

2. Generate a Line Number Mapper

When using your custom JSON decoder, ensure it creates a mapping table like so:

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

In this table:

Each key corresponds to the JSON path (or where the element is located).

The associated values represent the line numbers in the original JSON file.

3. Link the Mapper with Error Reporting

Now that you have this line number mapper, your JSON Schema validation process can leverage it. When an error is raised, you can look up the corresponding line number and append it to your error messages.

For instance, if there’s an error at data instance /bar, your output would look like:

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

Conclusion

By leveraging a custom JSON decoder that tracks line numbers, you can seamlessly enhance your error reporting during JSON validation. Although the built-in JSON processing in Python doesn’t include this feature by default, implementing a simple mapping system greatly improves debugging efforts. Now, when you encounter an error, you won’t just know what went wrong – you’ll also know exactly where to look in your JSON file.

Next time you face the issue of pinpointing JSON validation errors, remember that having access to line numbers can transform the way you troubleshoot your data. Happy coding!