python fifth week, the definition and use of functions, with code reuse recursive function

Understanding and definition of the function:

Effects: reduce the difficulty of programming and code reuse

definition: 

def <函数名> (<参数（0或多个）>):
    <函数体>
    return<返回值>    

parameter:

Parameters are divided into non-optional parameters and optional parameters , the first parameter is non-optional

Function definition is designed to be variable parameters , neither the total number of parameters determined

def fact (n,*b):
    s = 1
    for i in range (1,n+1):
        s*=i
    for item in b:
        s *=item
    return s
#>>>fact(10,3) 10886400
#>>>fact(10,3,5,8) 43545600

Parameter passing in two ways: the location and name of the transfer transfer

def fact (n,m=1):
    s = 1
    for i in range(1,n+1)
        s*=i
    return s//m

fact (10,5) and the fact (m = 5, n = 10) the result is the same

Function's return value: return

Function can return a value, or may not,

return 0 return value can be returned, the return value may be a plurality of pass

def fact(n,m=1):
    s = 1
    for i in range (1,n+1):
        s*=i
    return s//m,n,m
#>>>fact(10,5)    (725760,10,5)

#>>>a,b,c=fact(10,5) 
#print(a,b,c)   725760 10 5

Local variables and global variables ,

Internal functions for local variables, local variables change does not affect the overall:

Reserved words , Ltd. Free Join :

Internal global function using local variables can become global variables

If you create a local variable is not true, in a global variable

lambda functions:

<Function name> = lambda <parameter>: <expression> for simple definition can function, the function name is represented by a row in the return result

f = lambda x,y: x + y
f(10,15)
#25

And code reuse recursive function:

Code reuse:

The same code can be reused when needed:

Functions and objects are two major forms of code reuse

Function: the code will be named in the code level to establish a preliminary abstract

Object: Properties and Methods <a> <b> and <a> <b> () function again on tissue Abstract

Modular design, function or object encapsulation by dividing a program into expression between the modules and the module

Tight coupling: a lot of communication between the two portions, made five independent existence i

Loosely Coupled: less communication between the two portions, there may be independently

Internal modules tightly coupled, loosely coupled between the modules

Recursive function: they own tune

Even key features:

Chain: there is a recursive calculation process chain

EXAMPLE group: one or more groups present embodiment does not require re-recursive

def fact(n):
    if n == 0:
        retutn 1#基例
    else :
        return n *fact(n-1)#链条

Tower of Hanoi:

count  = 0
def hanoi(n,a,b,c):
    global count
    if n == 1
        print("{}:{}->{}".format(1,a,b)
        count += 1
    else:
        hanoi(n-1,a,c,b)
        print("{}:{}->{}".format(n,a,b))
        count += 1
        hanoi(n-1,c,b,a)