002_ Part III _[function/higher order function/adorner]

I. Higher-order functions:

• Sequential sorting

enumerate ([1,2 ,3 , 4, 5]) For idx, item  in enumerate ([1, 2, 3, 4]):     print (IDEX)      print (item) Def sort (*args):     ret = []    for  item in args:        for i, v in  Enumerate (ret):            if item >  v:                 Ret.insert (I,item)                  break        else:             ret.append (item)     return retsort (3, 1, 2,  5) 

• Reverse order
  

Def sort (F, *args):     ret = []    for item  in args:        for i, v in enumerate ( RET):            if f:                 if item >= v:                      ret.insert (I,item)                      break             else:                 if item <= v:                     ret.insert (I,item)                      break        else:             ret.append (item)      return retsort (true, 3, 1, 2, 5)

• Higher-order functions
  

def sort (Cmp, *args):     ret =  []    for item in args:         for i, v in enumerate (ret):          &NBSP;&NBSP;&NBSP;IF&NBSP;CMP (ITEM,&NBSP;V):                 ret.insert (I, item)                  break        else:             ret.append (item)      RETURN&NBSP;RETDEF&NBSP;CMP1 (x, y): &NBSP;&NBSP;&NBSP;&NBSP;RETURN&NBSP;X&NBSP;>=&NBSP;YDEF&NBSP;CMP2 (x ,  y):     return x <= ysort (cmp1, 3, 1, 2, 5) [5, &NBSP;3,&NBSP;2,&NBSP;1] 

Two. Special functions [built-in functions]:

1.filter the output returns a value of True based on the Boolean return value:

def bigger_5 (x): if x > 5:return True return falsefilter (bigger_5, Range) List (filter (Bigger_5, Range ( )) >[6, 7, 8, 9]

An iterator to the return value in the 2.map output function:

format: Map (func, seq1[, seq2 ...])

Example 1:

def bigger_5 (x): if x > 5:return True return falsemap (bigger_5, Range ()) list (map (bigger_5, Range (10))) & Gt [False, False, False, False, False, False, True, True, true, True]

Example 2:

DEF Inc (X): return x + 1list (Map (inc,[1, 2, 3, 4)) >[2, 3, 4, 5]list (Map (Inc,range (3))) >[1, 2, 3]

Example 3:

List (map (lambda x:x + 1,range (3))) >[1, 2, 3]

Example 4:

A = map (lambda x:x + 1,range (3)) next (a) >1next (a) >2next (a) >3next (a) >stopiteration

3.reduce

Format: Reduce (func, seq[, Init])

The reduce function is a simplification, which is a process in which the last iteration result (the element with the first init, such as the first element of the SEQ without init), executes a two-dollar func function with the next element, each iteration. In the reduce function, init is optional and, if used, is used as the first element of the first iteration.

n = 5print reduce (lambda x, y:x * y, Range (1, n + 1)) # 120

m = 2n = 5print reduce (lambda x, y:x * y, Range (1, n + 1), M) # 240

4.lambda

def sort (CMP, *args): ret = [] for item in Args:for I, V in Enumerate (ret): If CMP (item, v): Ret.insert (i, item) break Else:ret.append (item) return Retsort (lambda x, y : X >= y, 3, 1, 2, 5)

5. function as return value

def make_ic (f=1): Def Inc (X): return x + F return incinc1 = Make_ic (1) inc1 (5) >6

Currying

def bigger (x): def inner_bigger (y): return y > x return inner_biggerlist (Filter (bigger (5), Range ()) > [6, 7, 8, 9]

Three. Functools Library

1.partial [Set default parameters, late can be passed by keyword parameters]

To see if the object is callable:

From Functools import Partialimport pymysqlcallable (bigger_3) bigger_3 = partial (bigger,y=3) connect = partial ( Pymysql.connect, user= ' root ', password= ' xxxx ', database= ' xxxx ', port=3306 ' Connect (host= ' 127.0.0.1 ')

Four. Decorative Device

The essence of an adorner is a function that takes a function as a parameter, returns a function, and usually returns a function that adds a number of statements before and after the incoming function is executed, so called decoration;

• General Decoration Device

#第一种写法

def Timeit (FN): Def wrap (*args, **kwargs): start = Time.time () ret = fn (*args,**kwargs) print (Time . Time ()-start) return ret return wrapdef sleep (x): Time.sleep (x) Timeit (Sleep) (3)

The second method:

def Timeit (FN): Def wrap (*args, **kwargs): start = Time.time () ret = fn (*args,**kwargs) print (Time . Time ()-start) return ret return wrap@timeitdef sleep (x): Time.sleep (x) sleep (3)

Time.time ()//Get is a natural time time.clock ()//Get is a CPU execution time, occupy CPU time;

2. Decorative Adorner with parameters

import timedef timeit (process_time=false):     cacl = time.clock if process_time else time.time     Def inner_timeit (FN):         def wrap (*args, **kwargs):             start = cacl             RET = FN (*args, **kwargs)              print (CAcl ()  - start)              return ret         return wrap    return inner_timeit@timeit (True) Def sleep ( x):     time.sleep (x) sleep (3) 

import timedef timeit (process_time=false):     cacl = time.clock if process_time else time.time     Def inner_timeit (FN):         def wrap (*args, **kwargs):             start = cacl ()              RET = FN (*args, **kwargs)              print (CAcl ()  - start)              return ret         return wrap    return inner_timeitdef sleep (x):     time.sleep (x) Timeit (False) (Sleep) (3)    equivalent  timeit () (Sleep) (3) Timeit (True) (Sleep ) (3) 

import timedef timeit (process_time=false):     cacl = time.clock if process_time else time.time     Def inner_timeit (FN):         def wrap (*args, **kwargs):             start = cacl ()              RET = FN (*args, **kwargs)              print (CAcl ()  - start)              return ret         return wrap    return inner_timeit@timeit (True)   or   @timeit ()    or  @timeit (False) def sleep (x):     time.sleep (x) Sleep (3) 

#带参数的装饰器的基本结构def Make_timeit (): Def Timeit (): Def Inner_timeit (FN): Def wrap (*args, **kwargs):     RETURN fn (*args, **kwargs) return wrap return Inner_timeit return Timeit@make_timeit () ()    This is problematic because the syntax parser for Python only supports the correct wording of a parameter with the following time_2 = Make_timeit () @time_2 () or time_2 = Make_timeit () () @time_2def fn (): Pass

3. Practical Application of adorners:

Flask used a lot of decorations to do the routing.

[Flask.pocoo.org]

#利用装饰器进行权限控制

def check (allows): Def deco (FN): Def wrap (username, *args, **kwargs): If username in allows: RETURN fn (username, *args, **kwargs)//This line needs to correspond to wrap this line one by one return "not allow" return wrap re Turn Deco@check (["Comyn", "Mage"]) def private (username): print ("congratulation") Private ("Comyn")

4. Word document for function [wraps]:

def test ():         "         this is test          @return  None         '          passhelp (test) >help on function test in module __main__: Test ()     this is test     @return  noneimport time 

Def timeit (process_time=false):     cacl = time.clock if process_ Time else time.time    def inner_timeit (FN):         def wrap (*args, **kwargs):             start = cacl ()              RET = FN (*args, **kwargs)              print (CAcl ()  - start)              return ret        wrap.__name__ = fn.__name__         wrap.__doc__ = fn.__doc__         return wrap    return inner_timeit@timeit (True)    or  @timeit ()    or  @timeit (False) def sleep (x):     "         this is test         ' Sleep.__name__help ( Sleep

# Word document using wraps to implement functions

Import timefrom functools import wrapsdef timeit (Process_time=false):     cacl = time.clock if process_time else time.time          @wraps ()     def inner_timeit (FN):         def wrap (*args, **kwargs):             start = cacl ()              RET = FN (*args, **kwargs)              print (CAcl ()  - start)              return ret        return wrap     return inner_timeit@timeit (True)   or  @timeit ()    or @ Timeit (False) def sleep (x):      '         this is test          ' Sleep.__name__help (sleep)

This article from "Technical Side dishes" blog, declined reprint!

002_ Part III _[function/higher order function/adorner]