Python: Functions

Functions are well-organized, reusable pieces of code that are used to implement a single, or associated function.

Define and Invoke

def Add (x, y): ...      Print ('x=', x) #Python3必须加 "     ()" ... Print ('y='     , y) ... return x+y ... >>> Addx= 1y= 23

Parameter collection

#当参数不确定时, use * to define a function and return a tuple

 def  func (x,*arg):  print   (x) result  =x  print   for  i in   Arg:result  +=i  return   result  print  (func ( 1,2,3,4,5,6,7,8,9)) 

# returns the result 1    # corresponding to print (x)(2, 3, 4, 5, 6, 7, 8, 9)        # corresponding to print (ARG)    # Final Print (func (1,2,3,4,5,6,7,8,9)) Results    　　　　　　　　　　　　　　　

#当参数为赋值语句时, use * * to define the function and return a dictionary

def F (* *Karg): ...      Print (Karg) ... >>> f (a=1,b=2,c=3)        # When the argument is a non-assignment statement, the error {'C' a ' ' b ': 2}

* and * * Define function Synthesis Example

>>>defFoo (x,y,z,*arg,**karg): ...Print(x) ...Print(y) ...Print(z) ...Print(ARG) ...Print(Karg) ...>>> Foo ('Taylor', 1989,'Adele') Taylor1989Adele () {}>>> Foo (1,2,3,4,5)123(4, 5){}>>> Foo (1,2,3,4,5,name="Taylor")123(4, 5){'name':'Taylor'}

Summary of several definition methods

1. def a (P1,P2,P3) #参数的位置很重要
2. Def a (P1=V1,P2=V2) #定义的时候直接赋值
3. Def a (*arg) #适用不确定个数
4. Def a (**arg) #必须接收arg =val form

Several function lambda

>>> num=[1,2,3,4,5]>>> lam=Lambda x:x+1    # function directly after using the variable, After the variable is a colon-isolated expression, the result of the expression is the return value of the function >>> n=[] for in num: ...     N.append (Lam (i)) ... >>> n[2, 3, 4, 5, 6]

Map

Map (FUNC,SEQ), which executes the Func function on each element of an iterative object

>>> num=[1,2,3,4,5]>>> list (map (Lambda x:x+1,num))    #  Python3 need to convert map to list format, otherwise error, because direct use of map returned is iterators[2, 3, 4, 5, 6]

>>> l1=[1,2,3,4,5]>>> l2=[9,8,7,6,5]>>> list (map (lambda x, y: x+y,l1,l2)) [10, 10, 10, 10, 10]

Reduce

Reduce (FUNC,SEQ), Func must be a two-element operation function, first of all, the 1th, 2 data in the collection operation, the resulting result and the third data with the Func () function, and finally get a result. Horizontal operation.

 from import reduce   #Python3 cannot directly use the Reduce function, first refer to >>> reduce (lambda x,y:x +y,[1,2,3,4,5])     #"Sideways" calculated in turn 15

Filter

Filter (func, iterable), performs a func on the element in iterable and returns the element that satisfies func to the new list

>>> l=[1,2,3,4,5]>>> list (filter (lambda x:x>3,l))        #  Same reduce function [4, 5]

　　Equivalent statements

 for inch if x>3]        # ternary operator     [4, 5]#ifelse  Z If X is true, execute a=y if X is false, perform a=z

Python: Functions