file one.py

# file one.py
def func():
    print("func() in one.py")

print("top-level in one.py")

if __name__ == "__main__":
    print("one.py is being run directly")
else:
    print("one.py is being imported into another module")

file two.py

# file two.py
import one        # start executing one.py

print("top-level in two.py")
one.func()

if __name__ == "__main__":
    print("two.py is being run directly")
else:
    print("two.py is being imported into another module")

当运行python one.py，输出:

top-level in one.py
one.py is being run directly

当运行python two.py,输出:

top-level in one.py
one.py is being imported into another module
top-level in one.py
func() in one.py
two.py is being run directly