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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