函數式編程複習：
def map_test(func,array): array_new=[] for i in array: array_new.append(func(i)) return array_new print map_test(lambda x:x**2,range(10)) print map(lambda x:x**2,range(10)) def odd(num): return num % 2 def filter_test(func,array): array_new=[] for i in array: if func(i): array_new.append(i) return array_new print filter_test(odd,range(10)) print filter(odd,range(10)) def reduce_test(func,array,init): l=list(array) if init is None: res=l.pop(0) else: res=init for i in l: res=func(res,i) return res print reduce_test(lambda x,y:x+y,range(100),10) print reduce(lambda x,y:x+y,range(100),10)
python裝飾器
一:函數調用順序：其他高級語言類似,Python 不允許在函數未聲明之前,對其進行引用或者調用
錯誤示範：
def foo(): print 'in the foo' bar() foo() 報錯： in the foo Traceback (most recent call last): File "<pyshell#13>", line 1, in <module> foo() File "<pyshell#12>", line 3, in foo bar() NameError: global name 'bar' is not defined
def foo(): print 'foo' bar() foo() def bar(): print 'bar' 報錯：NameError: global name 'bar' is not defined
正確示範:(注意，python爲解釋執行，函數foo在調用前已經聲明瞭bar和foo，所以bar和foo無順序之分)
def bar(): print 'in the bar' def foo(): print 'in the foo' bar() foo() def foo(): print 'in the foo' bar() def bar(): print 'in the bar' foo()
二：高階函數
滿足下列條件之一就可成函數爲高階函數
某一函數當做參數傳入另一個函數中
函數的返回值包含n個函數,n>0
高階函數示範：
def bar(): print 'in the bar' def foo(func): res=func() return res foo(bar)
高階函數的牛逼之處：
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)() 等同於bar=foo(bar)然後bar() bar=foo(bar) bar()
三：內嵌函數和變量作用域：
定義：在一個函數體內創建另外一個函數，這種函數就叫內嵌函數(基於python支持靜態嵌套域)
函數嵌套示範：
def foo(): def bar(): print 'in the bar' bar() foo() # bar()
局部作用域和全局作用域的訪問順序
x=0 def grandpa(): # x=1 def dad(): x=2 def son(): x=3 print x son() dad() grandpa()
局部變量修改對全局變量的影響
y=10 # def test(): # y+=1 # print y def test(): # global y y=2 print y test() print y def dad(): m=1 def son(): n=2 print '--->',m + n print '-->',m son() dad()
四：閉包：如果在一個內部函數裏，對在外部作用域(但不是在全局作用域）的變量進行引用，那麼內部函數就被認爲是 closure
def counter(start_num=0): count=[start_num] def incr(): count[0]+=1 return count[0] return incr print counter() print counter()() print counter()() c=counter() print c() print c()
五：內嵌函數+高階函數+閉包=》裝飾器
預熱兩個範例:
範例一：函數參數固定
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(test)('alex')範例二：函數參數不固定
def decorartor(func):
def wrapper(*args,**kwargs):
print 'starting'
func(*args,**kwargs)
print 'stopping'
return wrapper
def test(n,x=1):
print 'in the test arg is %s' %n
decorartor(test)('alex',x=2)無參裝飾器
import time 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 @decorator def test(list_test): for i in list_test: time.sleep(0.1) print '-'*20,i #decorator(test)(range(10)) test(range(10))
2. 有參裝飾器
import time def 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(10)) test(range(10))
六：裝飾器應用案例：
裝飾器功能：函數超時則終止
# -*- coding: utf-8 -*-
from threading import Thread
import time
class TimeoutException(Exception):
pass
ThreadStop = Thread._Thread__stop#獲取私有函數
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)