创建型模式-单例模式（使用模块实现）
singletion模块
class Test():
pass
a = Test()
调用模块
from singleton.test import a
if __name__ == "__main__":
for item in range(10):
b = a
print(id(b))
singletion模块
class Test():
pass
a = Test()
调用模块
from singleton.test import a
if __name__ == "__main__":
for item in range(10):
b = a
print(id(b))