python 抽象

抽象

创建函数
>>> def hello(name):
 return 'hello,'+name+'!'

>>> hello('qiaochao')
'hello,qiaochao!'

函数注释
1）以#开头
2）直接写上字符串

函数定义可以嵌套
>>> def foo():
 def bar():
  print 'hello aaa '
 bar()
 
>>> foo()
hello aaa

函数递归调用：
>>> def jiecheng(n):
 if n == 1 :
  return 1
 else:
  return n*jiecheng(n-1)
 
>>> jiecheng(10)
3628800

二元查找：
def search(sequence,number,lower,upper):
 if lower == upper :
  assert number == sequence[upper]
  return upper
 else :
  middle = (lower + upper) // 2
  if(number > sequence[middle]):
   return search(sequence,number,middle+1,upper)
  else:
   return search(sequence,number,lower,middle)

print search([1,2,3,4,5,6,7,8,9,10],7,0,9)
6

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>>> def hello(greeting,name):
 print '%s , %s!' % (greeting,name)
  
>>> hello(greeting='hello',name='qiaoc')
hello , qiaoc!
注意：这里可以指定参数传值，这样就不会担心值对应的参数对不对 --- 关键字参数

>>> def hello(greeting='hi ',name='qiaochao'):
 print '%s , %s!' % (greeting,name)

>>> hello()
hi  , qiaochao!
注意：定义函数可以让参数有默认值

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收集参数

>>> def print_params(title,*params):
 print title
 print params

>>> print_params('Params:',1,2,2)
Params:
(1, 2, 2)
>>> print_params('ass :')
ass :
()
注意：*的意思是收集参数，如果不提供任何供收集的元素，params就是个空元组

>>> def print_params_1(**params):   -----** 字典参数
 print params

>>> print_params_1(x=1,y=2,c=3)
{'y': 2, 'x': 1, 'c': 3}

>>> def print_params_2(x,y,z=3,*params,**keybar):
 print x,y,z
 print params
 print keybar

>>> print_params_2(1,2,3,5,6,7,foo=1,bar=2)
1 2 3
(5, 6, 7)
{'foo': 1, 'bar': 2}
>>> print_params_2(1,2)
1 2 3
()
{}

反转过程
>>> def add(x,y):
 return x+y

>>> params=(1,2)
>>> add(*params)
3

** --- 也适用于字典参数

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全局变量   ----  global 定义
>>> x=1
>>> def change_global():
 global x
 x=x+1

>>> x
1
>>> change_global()
>>> x
2

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