Function basis of python basic introduction

**python function** 
1. The def name 
    The def name creates a new function object at runtime and assigns a variable name. 
    A def statement can appear where any statement can appear (all language names in python are run in real time, without compiling such a 
    process), or even nested within other statements. 
    Example: 
        def func(x,y): 
                print(x+y) 
        ------------------Separation line-------------- ---------- 
        if a==1: 
            def func(x,y): 
                print(x+y) 
        else: 
            def func1(x,y): 
                print(xy) 
Second, function parameter 
    1 , Formal parameter: the variable name in the circle after the function name when defining the function 
    2. Actual parameter: the value passed to the function when calling the 
    function , the number of calls must be the same as the declaration. 
    **Note: The formal parameters and actual parameters should be consistent when passing 
    , otherwise an error will be reported. 4. Named parameters: Parameters can be passed in random order, that is, the determined incoming parameter values ​​can be skipped. Pass parameter values ​​that are not passed 
        def func(x,y):
            return x+y 
        print(func(x=1,y=2)) 
    5. Default parameters: default parameters, generally in order from right to left, if there is no default parameter, 
        def func(x=1,y =2): 
            return x+y 
        print(func()) 
        ------------------Separation line---------------- -------- 
        def func(x,y=2): 
            return x+y 
        print(func(5)) 

    6. Parameters not counting the length: Sometimes, our function may need more values, but we cannot Determined at the formal parameter, then you need to pass the parameter indefinitely 

        def func(*var): 
             print(var) 

        func(1,2,3) 
        ----------------- -dividing line----------------------- 
        def func1(**var): 
             print(var) 
        func1(a=1,b=2) 
        return A dictionary, the key is a, the value is 1 and so on 
, the return value
    1. There is a return value: the key word return, and can return multiple values ​​return (a, b, c), when multiple values ​​are returned, it is a tuple 

    2, there can be no return value