Introduction to Python (v) Definition of function

Definition of functions in Python
Start with Def, followed by the name of the function definition and ()) ' Define parameters in parentheses ' with a colon, and zoom, return ends
Such as:

 def  hello (ming):         print ming         

Pass parameters:

ming=[1,2,3]
Ming= "OK"
As shown above, the variable is of no type and can be a list of STR
Parameters are divided into

必备参数关键字参数默认参数不定长参数

Required Parameters:

 def  hello (ming):         print ming         return 调用函数hello()；

Then there will be an error

Keyword parameters:

 def  hello (ming):         print ming         return 调用函数hello(ming="ok")；

The output is OK.

Default function:

 def  hello (n,m=10):         print n         print m调用函数hello(n=20,m=20)；hello(n=100

return value
N=20 m=20
n=100 m=10
Variable length parameter:

 def  hello (*args):         print args         return 调用函数hello(1);hello(1,2,3,4)

Output
1
1,2,3,4
Anonymous functions:

正常函数： def  hello (n,m):         print n*m匿名函数：lambda n,m:n*m

Multiple formal parameters:

 def  hello (a,*args,**kwargs):         print args         return 调用函数hello(1,2,3,4,n=1,m=2)

Output:
1
(2,3,4)
{N:1,m:2}
Higher order functions:

map是计算乘积的高阶函数def hello(x):    print x * xmap(hello,[1,2,3,4])输出相同：1，4，9，16reduce是计算累计的高阶函数def hi (x,y):    print x+yreduce(hi,[1,2,3,4])    输出同样一样：15

Sorted sorting is more used in higher-order functions.

n = [5,7,6,3,4,1,2] m = sorted(n)      print n[5, 7, 6, 3, 4, 1, 2] print m[1, 2, 3, 4, 5, 6, 7]

 A=dict(a=1,c=2,b=3,d=4)如果我们直接排序print（sorted(A)）[‘a‘, ‘b‘, ‘c‘, ‘d‘] print(sorted(A.item(), key=lambda x:x[1]) )           [(‘a‘, 1), (‘b‘, 2), (‘c‘, 3), (‘d‘, 4)]按倒叙排序 print(sorted(A.item(), key=lambda x:x[1]，reverse=True) )     [(‘d‘, 4), (‘b‘, 3), (‘c‘, 2), (‘a‘, 1)]

Introduction to Python (v) Definition of function