作用：當模塊被直接運行時，以下代碼塊將被運行，當模塊是被導入時，代碼塊不被運行。

例子：

# 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
import
 
 one

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")

如果你執行one.py文件，

python one.py
會輸出：

top-level in one.py
one.py is being run directly
如果你執行two.py文件，

python two.py
會輸出：

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

總結：當模塊導入時if __name__ == "__main__" 代碼塊不被執行，寫if __name__ == "__main__"是為了防止模塊導入，導致又重新運行了一遍導入的模塊的代碼。

if __name__ == "__main__" 的作用