Bad Magic Number: Understanding the Import Error

When working with Python, encountering the "Bad magic number" ImportError can be frustrating. This error indicates a corrupted pyc file, the compiled version of your Python script, which leads to an incompatibility with the Python interpreter.

Understanding the Magic Number

In UNIX-type systems, files begin with a special marker, known as a magic number, indicating the file type. Python incorporates a similar concept into its pyc files when created, ensuring verification during loading.

Causes of the Error

The "Bad magic number" error arises when the magic number in a pyc file is damaged. This can occur due to:

• Editing the pyc file directly
• Running the pyc file with a different Python version from which it was compiled
• File corruption or system errors

Resolving the Issue

To resolve this error, follow these steps:

• Delete the corrupted pyc files using rm *.pyc.
• If the pyc files belong to external modules, you will need to contact the developer for the py files and recompile them.

Intermittent Import Issues

In rare cases, the import error may occur intermittently. This can be due to the problematic pyc file only being imported under specific conditions. Examine the full stack trace when the error occurs for more details.

Magic Number Values

The first word of a pyc file represents the magic number. Its value depends on the Python version:

Python Version | Magic Number
--------------|----------------
2.5.1(r251)    | 62131
2.6.1(r261)    | 62161

A complete list of magic number values can be found in Python/import.c for your reference.