Functional programming of basic Python functions

One. Anonymous functions

An anonymous function is a specified function that does not need to be displayed, and frees up memory space as soon as it runs once.

The main forms of expression are:

Lambda Parameters: Specific functions

def Calc (n):     return n**nprint(calc# to anonymous function lambda n:n** N Print (Calc (10))

　　You may say that it is not convenient to use this thing. Oh, if it is so used, there is no yarn improvement, but the anonymous function is mainly used with other functions, as follows

res = map (lambda x:x**2,[1,5,7,4,8]) for in Res:    print(i)

Output
1
25
49
16
64

l=[3,2,100,999,213,1111,31121,333]print(max (l)) dic={'K1' : Ten,'K2': +,'k3': $Print (Max (DIC)) Print (Dic[max (dic,key=Lambda k:dic[k]))

Two. Functional programming

　　1. Higher-order functions

Any one of the following two features is a higher-order function:

(1) The passed-in parameter of the function is a functional name

(2) The return value of a function is a functional name

def foo ():
    Print ("from the Foo")
def test (func):
    return func

res = Test (foo)
Res ()

foo = Test (foo)
Foo ()

2. Functional programming: function = function of programming language definition + function of mathematical meaning

In layman's terms, the function is to use the programming language to implement mathematical functions. In this function, the object is immutable, either the parameter is a function, or the return value is a function, there is no for and while loop, all loops are implemented by recursion, no variable assignment (that is, without the variable to save the state), no assignment is not changed.

3.

array=[1,3,4,71,2]ret=[] forIinchArray:ret.append (i**2)Print(ret)#If we have 10,000 lists, then you can only define the above logic as a functiondefmap_test (Array): RET=[]     forIinchArray:ret.append (i**2)    returnretPrint(Map_test (array))#If our needs change, not to put each element in the list squared, plus 1, minus one, then you candefadd_num (x):returnX+1defmap_test (Func,array): Ret=[]     forIinchArray:ret.append (func (i))returnretPrint(Map_test (add_num,array))#You can use anonymous functionsPrint(Map_test (LambdaX:x-1, array))#this is the function of the map function, and the result of the map is that the object can be iteratedPrint(Map (LambdaX:x-1,range (5))) map function

map Function

4.

 fromFunctoolsImportReduce#Merge, get a result of mergingarray_test=[1,2,3,4,5,6,7]array=range (100)#error, RES does not specify an initial valuedefreduce_test (Func,array): l=list (array) forIinchL:res=func (res,i)returnRes#Print (Reduce_test (lambda x,y:x+y,array))#You can pop the first value from the left of the listdefreduce_test (Func,array): l=List (array) res=l.pop (0) forIinchL:res=func (res,i)returnResPrint(Reduce_test (Lambdax,y:x+Y,array))#we should support the user to pass in the initial value themselvesdefReduce_test (func,array,init=None): l=list (array)ifInit isNone:res=l.pop (0)Else: Res=Init forIinchL:res=func (res,i)returnResPrint(Reduce_test (Lambdax,y:x+Y,array))Print(Reduce_test (Lambdax,y:x+y,array,50)) Reduce function

Reduce function

5.

#The movie Theater gathered a bunch of idiots watching movies BB, let's find out what theymovie_people=['Alex','Wupeiqi','Yuanhao','Sb_alex','Sb_wupeiqi','Sb_yuanhao']defTELL_SB (x):returnX.startswith ('SB')deffilter_test (Func,array): Ret=[]     forIincharray:iffunc (i): Ret.append (i)returnretPrint(Filter_test (tell_sb,movie_people))#function filter to return an iterative objectPrint(Filter (LambdaX:x.startswith ('SB') , movie_people)) filter function

Filter Function

#of course, map,filter,reduce, you can handle all data types.Name_dic=[    {'name':'Alex',' Age': 1000},    {'name':'Wupeiqi',' Age': 10000},    {'name':'Yuanhao',' Age': 9000},    {'name':'Linhaifeng',' Age': 18},]#filter out the Millennium King by using filter eight, the turtle, and a 9,000-year-olddeffunc (x): Age_list=[1000,10000,9000]    returnx[' Age'] not inchAge_listres=filter (Func,name_dic) forIinchRes:Print(i) Res=filter (Lambdax:x[' Age'] = = 18, Name_dic) forIinchRes:Print(i)#reduce is used to calculate 1 to 100 and fromFunctoolsImportReducePrint(Reduce (LambdaX,y:x+y,range (100), 100))Print(Reduce (LambdaX,y:x+y,range (1,101)))#use map to process the list of strings, and turn everyone in the list into SB, for example ALEX_SBname=['Alex','Wupeiqi','Yuanhao']res=map (Lambdax:x+'_SB', name) forIinchRes:Print(i) Summary

Summary

Functional programming of basic Python functions