When working with Python, I came across an error message that says "ValueError: attempted relative import beyond top-level package." This error puzzled me for hours so I assumed it would give issue to other developers. Having just created a CLI for a project (link at bottom) this error held me up for a while. In this blog we'll check out what this error means, why it occurs, and (hopefully) how to prevent it.
Understanding the Error
The error message "ValueError: attempted relative import beyond top-level package" happens when your relative imports attempt to go beyond the top-level in your project's directory structure. Python's import system is designed with modular programming and reusability, but there are rules and syntax that must be followed to ensure the desired import behavior.
Causes of the Error
Incorrect Relative Imports: Relative imports are used to import modules from the same package/subpackages. If you try to perform a relative import that goes beyond the top-level package, the python interpreter cannot determine the correct file to import.
Inconsistent Module Structure: If your project's directory structure is not organized properly, it can lead to further issues when trying to utilize relative imports.
Example Scenario
Let's consider a scenario where you have the following directory structure:
my_project/
|----cli.py
|----subpackage1/
|----|----database.py
|----subpackage2/
|----|----other_code.py
In this case, if you try to use a relative import in the other_code.py file like 'from ..subpackage1.database import session' you'll encounter the "ValueError: attempted relative import beyond top-level package" error because the the interpreter is using this as a relative import from the cli.py file and it is already the top-most directory.
Solution
Absolute Imports: Instead of relying on relative, try absolute imports, that will ensure the modules are imported from the correct package. For example, if you want to import database.py from subpackage1, use 'from subpackage1.database import session'.
Run Scripts Properly: If you're running a script using the command line, ensure that your working directory is the root directory of your project. This can help Python locate modules correctly. I only ran the cli.py file in my project and it was in the top most directory.
Conclusion
Database Session Management: I used this code to properly set up the session to avoid duplicate database connections. This was achieved using the following code snippet:
With this it used the absolute path to my database connection. That way I could import the session object into any file in my project without the system creating a blank 'phase3_database.db' file in the topmost directory every time I ran my cli.py file. It gave the python interpreter the absolute path to the to session object. If the python interpreter was running a file that was deeper in the structure than the cli.py file it used the absolute path instead of the relative path. I also structured my project file tree to all stem from where cli.py was located so I could use absolute imports. That made sure I never ran into this error again.
I hope this helps you avoid the "ValueError: Attempted Relative Import Beyond Top-Level Package" error. Especially when using SQLAlchemy with your own database.
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