简单了解Python中的几种函数

>>> g = lambda x,y:x+y #x+y,并返回结果
>>> g(3,4)
7
>>> (lambda x:x**2)(4) #返回4的平方
16

>>> lamb = [ lambda x:x,lambda x:x**2,lambda x:x**3,lambda x:x**4 ]
>>> for i in lamb:
...   print i(3),
... 
3 9 27 81

>>> items = [1,2,3,4,5]
>>> squared = []
>>> for i in items:
...   squared.append(i**2)
... 
>>> squared
[1, 4, 9, 16, 25]

>>> def sqr(x): return x**2
... 
>>> map(sqr,items)
[1, 4, 9, 16, 25]

>>> map(lambda x: x**2, items)
[1, 4, 9, 16, 25]

>>> [ x**2 for x in items ]   #这个我最喜欢了，一般情况下速度足够快，而且可读性强
[1, 4, 9, 16, 25]

>>> lst1 = [1,2,3,4,5]
>>> lst2 = [6,7,8,9,0]
>>> map(lambda x,y: x+y, lst1,lst2)   #将两个列表中的对应项加起来，并返回一个结果列表
[7, 9, 11, 13, 5]

>>> lst1 = [1,2,3,4,5]
>>> lst2 = [6,7,8,9,0]
>>> lst3 = [7,8,9,2,1]
>>> map(lambda x,y,z: x+y+z, lst1,lst2,lst3)
[14, 17, 20, 15, 6]

>>> reduce(lambda x,y: x+y,[1,2,3,4,5])
15

>>> reduce(lambda x,y: x+y,[1,2,3,4,5],100)
115

>>> numbers = range(-5,5)
>>> numbers
[-5, -4, -3, -2, -1, 0, 1, 2, 3, 4]

>>> filter(lambda x: x>0, numbers) 
[1, 2, 3, 4]

>>> [x for x in numbers if x>0]   #与上面那句等效
[1, 2, 3, 4]

>>> filter(lambda x: x > 3, [1,2,3,4,5]) 
[4,5]

filter(...)
  filter(function or None, sequence) -> list, tuple, or string
  
  Return those items of sequence for which function(item) is true. If
  function is None, return the items that are true. If sequence is a tuple
  or string, return the same type, else return a list.