Special syntax in Python: filter, map, reduce, lambda introduction, pythonlambda

Special syntax in Python: filter, map, reduce, lambda introduction, pythonlambda

Filter (function, sequence ):Execute function (item) in sequence for items in sequence, and combine items with the execution result of True into a List/String/Tuple (depending on the sequence type) to return:
Copy codeThe Code is as follows:
>>> 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 ):Execute function (item) in sequence for items in sequence. See the execution result to form a List and return:
Copy codeThe Code is as follows:
>>> Def cube (x): return x * x
>>> Map (cube, range (1, 11 ))
[1, 8, 27, 64,125,216,343,512,729,100 0]
>>> Def cube (x): return x + x
...
>>> Map (cube, "abcde ")
['A', 'bb ', 'cc', 'dd', 'ee']

In addition, map also supports multiple sequence, which requires that the function also supports the corresponding number of parameter inputs:
Copy codeThe Code is as follows:
>>> 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 ):Call the function sequentially for items in sequence. If starting_value exists, it can also be called as an initial value. For example, it can be used to sum the List:
Copy codeThe Code is as follows:
>>> Def add (x, y): return x + y
>>> Reduce (add, range (1, 11 ))
55 (Note: 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10)
>>> Reduce (add, range (1, 11), 20)
75 (Note: 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 20)

Lambda:This is an interesting syntax supported by Python. It allows you to quickly define the smallest function of a single row. Similar to Macros in C, these lambda functions are borrowed from LISP, it can be used in any function:
Copy codeThe Code is as follows:
>>> G = lambda x: x * 2
>>> G (3)
6
>>> (Lambda x: x * 2) (3)
6

We can also combine filter map reduce and lambda to write a simple row of functions.
For example:
Copy codeThe Code is as follows:
Kmpathes = filter (lambda kmpath: kmpath,
Map (lambda kmpath: string. strip (kmpath ),
String. split (l ,':')))

It looks troublesome. In fact, it is as elegant as it is to describe the problem in a language.
Splits all elements in l by ':' To produce a list. Strip each element of the List to form a list. Perform a direct return operation on each element in the list (filter conditions can be added here) to obtain a list separated, each string in the list is strip and can filter special strings.