对Python生成器、装饰器、递归的使用详解

 更新时间:2019年07月19日 09:16:49   作者:Field_Yang   我要评论
今天小编就为大家分享一篇对Python生成器、装饰器、递归的使用详解,具有很好的参考价值,希望对大家有所帮助。一起跟随小编过来看看吧

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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