对Python生成器、装饰器、递归的使用详解

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

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