Python Special Syntax: filter, map, reduce, lambda

filter (function, sequence): Executes function (item) on item in sequence, and the item that executes the result of true is composed of a list/string/ The Tuple (depending on the type of sequence) returns:
>>> def f (x): return x% 2! = 0 and x% 3! = 0
>>> filter (F, Range (2, 25))
[5, 7, 11, 13, 17, 19, 23]
>>> def f (x): return x! = ' a '
>>> filter (F, "abcdef")
' Bcdef '

map (function, sequence) : Executes function (item) on item in sequence, and the result of execution consists of a list return:
>>> def Cube (x): Return x*x*x
>>> Map (cube, range (1, 11))
[1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
>>> def Cube (x): return x + x
...
>>> map (Cube, "ABCDE")
[' AA ', ' BB ', ' cc ', ' dd ', ' EE ']
In addition, the map supports multiple sequence, which requires that the function also supports the corresponding number of parameter inputs:
>>> def add (x, y): Return x+y
>>> Map (Add, Range (8), range (8))
[0, 2, 4, 6, 8, 10, 12, 14]

reduce (function, sequence, starting_value) : Calls the function for the item order in sequence, if there is starting_ Value, which can also be called as an initial value, for example, can be used to sum the list:
>>> def add (x, y): return x + y 
>>> Reduce (add, range (1, )  
55 (note: 1+2+3+4+5+6+7+8+9+10)
>>> Reduce (add, range (1, one),)  
75 (Note: 1+2+3+4+5+6+7 +8+9+10+20)

Lambda: This is a funny syntax for Python, which allows you to quickly define the smallest function of a single line, similar to a macro in C, these functions, called Lambda, are borrowed from Lisp and can be used wherever functions are needed:
>>> g = Lambda x:x * 2
>>> g (3)
6
>>> (Lambda x:x * 2) (3)
6


We can also use the filter map reduce and lambda together, the function can be simply written in one line.
For example
Kmpathes = Filter (lambda Kmpath:kmpath,
Map (Lambda Kmpath:string.strip (Kmpath),
String.Split (L, ': ')))
Looks like trouble, in fact, as in the language to describe the problem, very elegant.
Make a list of all the elements in L that are split with ': '. Each element of this list is made into a string strip, forming a list. Do a direct return operation on each element of this list (this place can be added to the filter limit) and eventually get a string that is ': ' In the split list, each string in the list is strip and can be filtered on a special string.

Python Special Syntax: filter, map, reduce, lambda