Python Base 4 Adorner

Python decorator

One: function call Order: Similar to other high-level languages, Python does not allow references to or calls to a function before it is declared
Error Demonstration:

def foo (): print ' in the Foo ' bar () Error: In the Foo Traceback (most recent call last): File "<pyshell#13 > ", Line 1, in <module> foo () File" <pyshell#12> ", line 3, foo bar () nameerror:global name ' Bar ' is not defined

def foo (): print ' foo ' bar () foo () def bar (): print ' bar ' ERROR: Nameerror:global name ' bar ' is not defined

Correct demonstration: (Note that Python is executed for interpretation, function Foo has declared bar and Foo before the call, so bar and Foo are not ordered)

def bar (): print ' in the bar ' def foo (): print ' in the Foo ' bar () foo () def foo (): print ' in the foo ' BA R () def bar (): print ' in the Bar ' foo ()

Second: higher-order functions

A function is a higher order function if one of the following conditions is met

1. Pass a function name as an argument to another function (adding functionality to the adorner function without modifying its source code)

2. The return value of the function contains n functions, n>0 (does not modify the function's Calling method)

High-order function demonstration:

def bar (): print ' in the bar ' def foo (func): Res=func () return Resfoo (BAR)

The beauty of higher-order functions:

def foo (func): return func print ' function body is%s '% (foo (bar)) print ' Function name is%s '% (foo (bar). Func_name) foo ( Bar) () #foo (bar) () is equivalent to Bar=foo (bar) and then bar () Bar=foo (bar) bar ()

Three: inline functions and variable scopes

Definition: Create another function inside a function called inline function (based on Python support for static nested fields)

Function Nesting Demonstration:

def foo (): Def bar (): print ' In the Bar ' () foo () # Bar ()

Access order of local scope and global scope

X=0def Grandpa (): # X=1 def dad (): x=2 def son (): x=3 print x son () da D () Grandpa ()

Effect of local variable modification on global variables

y=10# def Test (): # y+=1# print y def Test (): # Global y y=2 Print y test () Print Y def dad (): M=1 D EF Son (): n=2 print '---> ', m + N print '--', M Son () dad ()

Four: Closures: If in an intrinsic function, a reference to a variable in the outer scope (but not at the global scope), then the intrinsic function is considered closure

def counter (start_num=0): Count=[start_num] def incr (): Count[0]+=1 return count[0] return incr pri NT counter () print counter () () Print counter () () C=counter () print C () print C ()

Five: inline function + higher order function + closure = "Decorator

Two examples of preheating:

Example one: fixed function parameters

def decorartor (func): Def wrapper (n): print ' starting ' func (n) print ' stopping ' return wrapper def test (n): print ' in the test arg-is%s '%n decorartor (' Alex ')

Example two: The function parameter is not fixed

def decorartor (func): Def wrapper (*args,**kwargs): print ' starting ' func (*args,**kwargs) print ' St Opping ' return wrapper def Test (n,x=1): print ' in the test arg-is%s '%n decorartor (test) (' Alex ', x=2)

1. Non-parametric adorner

Import timedef decorator (func):         def wrapper (* Args,**kwargs):             start=time.time ()              func (*args,**kwargs)              stop=time.time ()              print  ' run time is %s  '  % (stop-start)              print timeout         return wrapper  @decoratordef  test (list_test):     for  i in list_test:        time.sleep (0.1)          print  '-' *20,i    #decorator (test) (range)  test (Range (10))

2. Parametric decorator

Import timedef timer (timeout=0):     def decorator (func):         def wrapper (*args,**kwargs):             start=time.time ()              func (*args,**kwargs)             stop= Time.time ()             print  ' Run time  is %s  '  % (stop-start)              print timeout        return wrapper     return decorator@timer (2) def test (list_test):    for i in  List_test:        time.sleep (0.1)          print  '-' *20,i   #timer (timeout=10) (test) (range) test (range (10)) 

Six: Decorator application case:

Adorner function: function timeout is terminated

# -*- coding: utf-8 -*-  from threading import thread   Import time     class timeoutexception (Exception):       pass     threadstop = thread._thread__stop# Get private Functions       def timelimited (Timeout):       def decorator ( function):           def decorator2 (*args,**kwargs):               class timelimited ( Thread):                   def __init__ (Self,_error= none,):                       thread.__init__ (self)                        self._error =   _error                                           def run (self):                       try:                            self.result = function (*args,**kwargs)                         except exception,e:                           self._error =e                      def _stop (self):                        if self.isalive ():                           threadstop (self)                  t =  timelimited ()               t.start ()               t.join (timeout)                         if isinstAnce (t._error,timeoutexception):                   t._stop ()                    raise timeoutexception (' timeout for %s '  %  ( Repr (function)))                   if t.isalive ():                   t._stop ()                    raise timeoutexception (' timeout for %s '  %  ( Repr (function)))                   if t._error is None:                   return t.result              return decorator2      return decorator    @ Timelimited (2)   def fn_1 (secs):       time.sleep (secs)        return  ' finished '          if __ name__ ==  "__main__":       print fn_1 (4)

This article from "Amin blog" blog, declined reprint!

Python Base 4 Adorner