python @staticmethod 注解，静态方法，可以省略类里那个self参数

class staticmethod(object):
    """
    staticmethod(function) -> method
    
    Convert a function to be a static method.
    
    A static method does not receive an implicit first argument.
    To declare a static method, use this idiom:
    
         class C:
             @staticmethod
             def f(arg1, arg2, ...):
                 ...
    
    It can be called either on the class (e.g. C.f()) or on an instance
    (e.g. C().f()).  The instance is ignored except for its class.
    
    Static methods in Python are similar to those found in Java or C++.
    For a more advanced concept, see the classmethod builtin.
    """