Python生成器、装饰器、递归

Python生成器、装饰器、递归

1、Python生成器表达式

1）、Python生成器表达式

语法格式：

(expr for iter_var in iterable)

(expr for iter_var in iterable ifcond_expr)

2）、自定义生成器

函数中使用yield，会返回一个生成器对象。yieldx

生成器使用示例：

In [1]:list((i**2 for i in range(1,11)))

Out[1]:[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

In [2]:def genNum(x):

  ...:    y = 0

  ...:    while y <= x:

  ...:        yield y

  ...:        y += 1

In [3]: g1= genNum(4)

In [4]:type(g1)

Out[4]:generator

In [5]:g1.next()

Out[5]:0

In [6]:g1.next()

Out[6]:1

In [7]:g1.next()

Out[7]:2

In [8]:g1.next()

Out[8]:3

In [9]:g1.next()

Out[9]:4

In [10]:g1.next()

---------------------------------------------------------------------------

StopIteration                            Traceback (most recent call last)

in()

----> 1g1.next()

StopIteration:

In [11]:def genNum(n):

  ....:    i = 1

  ....:    while i <= n:

  ....:        yield i ** 2

  ....:        i += 1

In [12]:g1 = genNum(20)

In [13]:for i in g1:

  ....:    print i,

  ....:    

1 4 9 1625 36 49 64 81 100 121 144 169 196 225 256 289 324 361400

2、Python装饰器

1）、装饰器本身是一个函数，用于装饰其它函数；

2）、功能：增强被装饰函数的功能；

装饰器一般接受一个函数对象作为参数，以对其进行增强

例1：装饰器使用示例

In [1]:def decorater(func):

  ...:    def wrapper():

  ...:        print "Just a Decorater!"

  ...:        func()

  ...:        raw_input('Please Input your name:')

  ...:    return wrapper

  ...:

In [2]:@decorater

   ...:def show():

  ...:    print "I am from China."

  ...:    

In [3]:show()

Just aDecorater!

I am fromChina.

PleaseInput your name:Fieldyang

例2：对能够传入参数的函数进行装饰

In [1]:def decorater(func):

  ...:    def wrapper(x):

  ...:        print "Just a Decorater!"

  ...:        func(x)

  ...:        raw_input('Please Input your name:')

  ...:    return wrapper

  ...:

In [2]:@decorater

   ...:def show(x):

  ...:    print "I am from China.%s" %x

  ...:    

In [3]:show('how are you ?')

Just aDecorater!

I am fromChina.how are you ?

PleaseInput your name:Fieldyang

3、Python递归

递归需要边界条件，递归前进段和递归返回段；

        10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 *1

        10 * （10-1）* （（10-1）-1）* ...

递归函数使用示例：

In [1]:def recursion(n):

  ...:    if n <= 1: return 1

  ...:    else: return n * recursion(n-1)

  ...:  

#递归函数相当于如下过程： 

In [2]: recursion(3) = 3 * recursion(2)= 3 * 2 *recursion(1)=3*2*1

KeyboardInterrupt

In [3]:recursion(3)

Out[3]:6

In [4]:recursion(4)

Out[4]:24

In [5]:recursion(5)

Out[5]:120

In [6]:recursion(10)

Out[6]:3628800