Python Learning routines-function parameters and recursion

First say recursion: Because the principle is simple, but to use flexibly, it is very difficult.

The principle of recursion is to call the function itself within the function to achieve the purpose of the loop,

such as a factorial function def fn (n):

If n==1:

return n;

else:

RETURN fn (n-1) *n;

There is also the idea of a tail recursion, because recursion is very easy to stack overflow, so the left function itself should not appear in the return value.

The above factorial can be converted to DEF fn (n,product):

If n==1:

return product;

else:

RETURN fn (n-1,n*product);

def use (n):

RETURN fn (n,1);

Again, the parameters of the function:

The parameters of the function are divided into 5 types, positional parameters, default parameters, variable parameters, keyword parameters, and specific keyword parameters.

In defining a function, these five types of parameters must be sequential, but some of them can be missing

Positional parameters are general parameters, Def F (A, B):

Pass

Default parameter: def f (a= "a"):

Pass

Can be called directly f (), or F ("B");

A variable parameter is one that can be used when the number of arguments is indeterminate, for example: Def f (*PRA):

Pass

The keyword parameter is def f (**kw):

Pass

Called when F (a= "a", b= "B");

The variable parameter is encapsulated as a tuple, and the keyword parameter encapsulates a dic;

The specific keyword parameter is def f (*,a= "A", b):

Pass

As can be seen from the definition, the parameter a can be called by default, B cannot be f ("B");

　　　　　　　　　　　　　　

Python Learning routines-function parameters and recursion