How Can I Prevent Unwanted Code Execution When Importing Modules in Python?

Python's Module Execution Mystery

In Python programming, it's possible to encounter unexpected behavior when importing modules. Consider a program that provides two modes of operation: user-interactive mode via main.py and batch mode via batch.py.

The problem arises when batch.py imports main.py but accidentally triggers the execution of its code. This occurs because Python treats keywords like class and def as executable statements rather than declarations.

Solution: Conditional Execution

To prevent this unwanted execution, Python offers a solution known as conditional execution. It involves encapsulating the code meant to run only when the module is called directly, not imported.

The following snippet demonstrates this approach:

# Code that can be executed both when called directly and imported
...

# Code to be executed only when called directly
def main():
    ...

# Conditional execution to only run 'main' when the module is called directly
if __name__ == "__main__":
    main()

In this pattern, any code placed outside the if __name__ == "__main__" block will be executed regardless of whether the module is imported or called directly. Code within this block will only be executed when the module is called directly, effectively preventing unwanted execution during imports.

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