def print_all(x,y,z):
print(z(x)+z(y))
print_all(3,3,get)
60
higher-order function:
define: at least satisify one in two condition .accept one or more function as input output one function ,function as variable.
function and method all object as variable.
function name actually is a variable name.
function can self assignment to variable . variable immediatly function.
if one variable point to function ,the variable can call the function.
function can use for a parameter.
in addition higher-order function also can as return value.
1:function name can be assignment
2:function name can be use for other function variable
3:function name can be use for other function return value