__name__ == '__main__'

# When you run a file directly:
#   __name__ == "__main__"
# When you import it as a module:
#   __name__ == "module_name"

# Example: calculator.py
def add(a, b):
    return a + b

def multiply(a, b):
    return a * b

# This code ONLY runs when executed directly
# NOT when imported as a module
if __name__ == "__main__":
    print("Running calculator.py directly!")
    print(f"5 + 3 = {add(5, 3)}")
    print(f"4 * 7 = {multiply(4, 7)}")
    
    # Run tests
    assert add(2, 3) == 5
    assert multiply(3, 4) == 12
    print("All tests passed!")

# If another file does 'from calculator import add':
# Only the functions are imported
# The test code does NOT run!

# This is the standard Python pattern.
# ALWAYS use it in your scripts.
print(f"\n__name__ = '{__name__}'")