Python function lambda (), filter (), map (), reduce ()

(1) Lambda

A lambda is a python that creates an anonymous function in the form of the following syntax:

Lambda [arg1[, arg2, ... argn]]: expression

Use examples:

#使用法一
fun = lambda x,y:x+y
print Fun (1,2)
#输出结果为:
3

#使用法二
print (lambda x,y:x+y) (1,2)
# Output:
3

#上面法一和法二相当于:
def func_1 (x, y): return
	x + y
print func_1 (1, 2)

(2) Map ()

Map (function, sequence): Performs a function (item) on the item in sequence, as the execution result consists of a list return. Examples are as follows:

def cube (x): Return
        x*x*x
print map (cube, range (1))
#输出结果为:
[1, 8, 27, 64, 125, 216, 343, 512, 729 , 1000]

(3) Reduce ()

Reduce (function, sequence, starting_value): Iterates the call function on the item order in sequence, and if there is a starting_value, it can also be invoked as an initial value. For example, you can use to sum the list:

def add (x,y): return
	x + y
print reduce (add, range (1))  
print reduce (add, range (1),

#输出结果为: 
  55 #1 +2+3+4+5+6+7+8+9+10
#1 +2+3+4+5+6+7+8+9+10+20

(4) filter ()
Filter (function, sequence): Performs a function (item) on the item in sequence, and makes an item that executes the result to true list/string/ Tuple (depending on the type of sequence) is returned. Examples are as follows

#例1
def f (x): Return
	x 2!= 0 and x 3!= 0 
print filter (f, Range (2)) 
#输出结果为:
[5, 7, 11, 13, 1 7,

#例2]
def f (x): Return
	x!= ' A ' 
print filter (F, "abcdef") 
#输出结果为:
' bcdef '