python内置函数filter,map,reduce
Python list function build in three useful funtion
(1):filter(funtion,sequence)
This function will return the item in the sequence invoke the function and return true
such as:
def f(x):if x > 0: return Trueelse: return False?
filter(f,range(-3,4))
will return(1,2,3)
(2):map(function,sequence[,sequence...])
This funcion will map all the sequence one by one, so the sequence list's size must be all the same.
for example:
def m(x,y,z): return x+y+z?
map(f,range(3),range(3),range(3))
will return
[0,3,6]
so, how many params the function has. how many sequence are needed
(3):reduce(function,sequence)returns a single value constructed by calling the binary function?function?on the first two items of the sequence, then on the result and the next item, and so on.
for example:
>>> def r(x,y): print 'x is %s, y is %s' % (x,y)>>> reduce(r,range(5))x is 0, y is 1x is None, y is 2x is None, y is 3x is None, y is 4?
?
?
So the function must take two params,
and there is a third param, use it to set the first param
for example:
>>> reduce(r,range(5),1)x is 1, y is 0x is None, y is 1x is None, y is 2x is None, y is 3x is None, y is 4?
?
