How to Handle Relative Imports in Python Packages When Running Modules as Scripts?

Relative Imports in Python 3

When attempting to import a function from another file in the same directory, using either from .mymodule import myfunction or from mymodule import myfunction can result in errors. The reason lies in whether the module containing the function being imported is inside a package or not.

Using Relative Imports

Relative imports work when the module is inside a package. To create a package, an __init__.py file must be present in the directory containing the modules. However, it's also important to ensure the module can be run as a script sometimes.

Code Structure

A common layout for a package containing multiple modules and a main script is as follows:

• main.py

• mypackage/

  • __init__.py
  • mymodule.py
  • myothermodule.py

Within mymodule.py:

# Exported function
def as_int(a):
    return int(a)

# Test function for module  
def _test():
    assert as_int('1') == 1

if __name__ == '__main__':
    _test()

Within myothermodule.py:

# Import exported function from the mymodule
from .mymodule import as_int

# Exported function
def add(a, b):
    return as_int(a) + as_int(b)

# Test function for module  
def _test():
    assert add('1', '1') == 2

if __name__ == '__main__':
    _test()

Within main.py:

# Import exported function from myothermodule
from mypackage.myothermodule import add

def main():
    print(add('1', '1'))

if __name__ == '__main__':
    main()

Running the Code

When running main.py or mypackage/mymodule.py, the code executes without issues. However, attempting to run mypackage/myothermodule.py results in an error related to the relative import used (from .mymodule import as_int).

Alternative Approaches

There are two alternative approaches to address this:

1. Use Absolute Imports: Replace the relative import with an absolute import by specifying the full module path: from mypackage.mymodule import as_int. However, this requires that the parent directory of the package is added to the PYTHONPATH.
2. Use the -m Option: To avoid using absolute imports while ensuring the module runs correctly, use the -m option with Python: python3 -m mypackage.myothermodule. This approach requires running the command from the parent directory of the package.

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