Solving the TypeError when Writing a List of Dictionaries to a JSON File in Python

Learn how to resolve the `TypeError: Object of type ObjectId is not JSON serializable` error when attempting to write a list of dictionaries to a JSON file in Python. This guide provides clear steps and explanations.
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Introduction

If you've ever tried to write a list of dictionaries to a JSON file in Python, you might have encountered an error that stops you in your tracks. One common issue is the TypeError: Object of type ObjectId is not JSON serializable. Understanding why this happens and how to fix it is essential for anyone working with JSON in Python.

In this post, we will explore the problem and provide a clear solution to help you write your list of dictionaries to a JSON file without running into serialization issues.

The Problem

You might have code that looks something like this:

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

When you run this code, you encounter the following error:

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

What’s Causing the Error?

The error arises because the ObjectId type, commonly used in MongoDB to represent unique identifiers, is not directly serializable to JSON by the json module in Python. The json module can only serialize standard Python types (like dictionaries, lists, strings, integers, etc.).

The Solution

To resolve this issue, you'll need to make a few adjustments to your data before trying to write it to a JSON file. Here are the steps to do that:

Step 1: Convert ObjectId to String

Since ObjectId cannot be directly serialized, you'll need to convert it to a string. You can achieve this by defining a function that converts ObjectId instances to strings and then applying that function to your list of dictionaries.

Here's a revised example:

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

Step 2: Validating the JSON Output

After running the updated code, you should now have a well-formed JSON file that looks like this:

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

Step 3: Check for Common JSON Format Errors

Ensure that your initial data structure adheres to JSON formatting rules:

JSON data must be enclosed in curly braces or brackets.

Keys must be strings enclosed in double quotes.

Strings must be in double quotes as well.

Example with Correct Formatting

Here's how your input data should be structured:

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

Conclusion

Handling serialization errors when working with JSON in Python can be tricky, especially with types like ObjectId. By converting ObjectId instances to strings and ensuring your data is correctly formatted, you can easily write lists of dictionaries to JSON files without encountering errors.

If you follow the outlined steps, you should now be able to manage your JSON data seamlessly. Happy coding!