Understanding the ModuleNotFoundError in Custom Python Packages

Learn how to resolve the `ModuleNotFoundError` when working with custom Python packages and modules. We'll guide you step-by-step through the solution.
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Troubleshooting ModuleNotFoundError in Custom Python Packages

If you're venturing into building your own Python packages, you might encounter some unexpected errors along the way. One common issue developers face is the infamous ModuleNotFoundError. This typically occurs when trying to access modules within a custom package. In this guide, we will dive deep into understanding this error and how to resolve it effectively.

The Problem: When Modules Become Unavailable

Consider the following directory structure of a simple Python package:

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In your __init__.py, you have the following code:

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And here’s what your modules look like:

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You encounter an error message like this:

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Understanding the Error

The error you’re facing arises from how Python is trying to access your modules in the package directory. When you specify import mod1 and import mod2 in your __init__.py, Python looks for these modules in the global scope, not within the package, which leads to the ModuleNotFoundError since they are not found there.

The Solution: Proper Import Statements

To resolve this issue, you need to make changes to how you import your modules within __init__.py. Follow these steps:

Updating __init__.py

Change the code in __init__.py to utilize relative imports:

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This syntax signals Python to look for mod1 and mod2 within the package, thereby alleviating the ModuleNotFoundError.

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Conclusion: Testing Your Changes

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Summary

To summarize, encountering a ModuleNotFoundError when accessing modules in a custom Python package is a common issue. Remember to use relative imports in your __init__.py and confirm that you are calling your functions accurately in your test script. With this solution, you'll be well on your way to successfully managing your custom Python packages!