函数式编程复习：
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def map_test(func,array): array_new=[] for i in array: array_new.append(func(i)) return array_newprint map_test(lambda x:x**2,range(10))print map(lambda x:x**2,range(10))def odd(num): return num % 2def filter_test(func,array): array_new=[] for i in array: if func(i): array_new.append(i) return array_newprint 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 resprint reduce_test(lambda x,y:x+y,range(100),10)print reduce(lambda x,y:x+y,range(100),10) |
python装饰器
一:函数调用顺序：其他高级语言类似,Python 不允许在函数未声明之前,对其进行引用或者调用
错误示范：
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def foo(): print 'in the foo' bar() foo()报错：in the fooTraceback (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 |
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def foo(): print 'foo' bar()foo()def bar(): print 'bar' 报错：NameError: global name 'bar' is not defined |
正确示范:(注意，python为解释执行，函数foo在调用前已经声明了bar和foo，所以bar和foo无顺序之分)
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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：高阶函数
满足下列条件之一就可成函数为高阶函数
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某一函数当做参数传入另一个函数中
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函数的返回值包含n个函数,n>0
高阶函数示范：
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def bar(): print 'in the bar'def foo(func): res=func() return resfoo(bar) |
高阶函数的牛逼之处：
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def foo(func): return funcprint 'Function body is %s' %(foo(bar))print 'Function name is %s' %(foo(bar).func_name)foo(bar)()#foo(bar)() 等同于bar=foo(bar)然后bar()bar=foo(bar)bar() |
三：内嵌函数和变量作用域：
定义：在一个函数体内创建另外一个函数，这种函数就叫内嵌函数(基于python支持静态嵌套域)
函数嵌套示范：
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def foo(): def bar(): print 'in the bar' bar()foo()# bar() |
局部作用域和全局作用域的访问顺序
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x=0def grandpa(): # x=1 def dad(): x=2 def son(): x=3 print x son() dad()grandpa() |
局部变量修改对全局变量的影响
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y=10# def test():# y+=1# print ydef test(): # global y y=2 print ytest()print ydef dad(): m=1 def son(): n=2 print '--->',m + n print '-->',m son()dad() |
四：闭包：如果在一个内部函数里，对在外部作用域(但不是在全局作用域）的变量进行引用，那么内部函数就被认为是 closure
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def counter(start_num=0): count=[start_num] def incr(): count[0]+=1 return count[0] return incrprint counter()print counter()()print counter()()c=counter()print c()print c() |
五：内嵌函数+高阶函数+闭包=》装饰器
预热两个范例:
范例一：函数参数固定
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def decorartor(func): def wrapper(n): print 'starting' func(n) print 'stopping' return wrapperdef test(n): print 'in the test arg is %s' %ndecorartor(test)('alex') |
范例二：函数参数不固定
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def decorartor(func): def wrapper(*args,**kwargs): print 'starting' func(*args,**kwargs) print 'stopping' return wrapperdef test(n,x=1): print 'in the test arg is %s' %ndecorartor(test)('alex',x=2) |
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无参装饰器
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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(10)) test(range(10)) |
2. 有参装饰器
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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(10))test(range(10)) |
六：装饰器应用案例：
装饰器功能：函数超时则终止
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# -*- coding: utf-8 -*- from threading import Thread import time class TimeoutException(Exception): pass ThreadStop = Thread._Thread__stop#获取私有函数 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)
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