Getting started with Python-functional programming

One feature of functional programming is that it allows the function itself to be passed as a parameter to another function, and also allows the return of a function

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Function

Defining functions

def my_abs (x):
    If x >= 0:
        return x
    Else
        Return-x


Result =my_abs (10)
Print (Result)

Advanced Features

Slice

Slice

L[:3]

Iteration

D = {' A ': 1, ' B ': 2, ' C ': 3}
For key in D:
   Print key  #注意这个缩进 instead of {}

For ch in ' ABC ':
  Print Ch

For x, y in [(1, 1), (2, 4), (3, 9)]:
  Print x, y

Function-Type programming

One feature of functional programming is that it allows the function itself to be passed as a parameter to another function, and also allows the return of a function

Python provides partial support for functional programming. Because Python allows the use of variables, Python is not a purely functional programming language.

def add (x, Y, f):
    return f (x) + f (Y)
Print Add ( -5, 6, ABS)

Results: 11

By passing functions as parameters, such functions are called higher-order functions, and functional programming refers to this highly abstract programming paradigm.

Map/reduce

If you read Google's famous paper "Mapreduce:simplified Data processing on Large Clusters", you can probably understand the concept of map/reduce.

mapFunctions the passed-in function sequentially to each element of the sequence and returns the result as a new list.

Reduce functions a function in a sequence [X1, x2, x3 ...] , the function must receive two parameters, and reduce calculates the result and the next element of the sequence, and the effect is:

#map
def f (x):
   return x * x
Print map (f, [1, 2, 3, 4, 5, 6, 7, 8, 9])

#reduce
DEF fn (x, y):
    Print x, y, × * + Y
    return x * ten + y
Print  reduce (FN, [1, 3, 5, 7, 9])

filter()Also receives a function and a sequence. and map() different, the filter() incoming function is applied sequentially to each element, and then True False the element is persisted or discarded based on the return value.

def is_odd (n):
    return n% 2 = = 1
Print filter (is_odd, [1, 2, 4, 5, 6, 9, 10, 15])

IO programming

Read the file

f = open (' D:\logs\log.txt ', ' R ')
Print F.read ()

Write a file

f = open ('/users/michael/test.txt ', ' W ')
F.write (' Hello, world! ')
F.close ()

# #-*-Coding:utf-8-*-

__author_= ' Yuchao '

Print "Hello world!"

Must be placed on the first line

TCP Programming

#
# #-*-Coding:utf-8-*-

# Import the Socket library:
Import socket
# Create a socket:
s = socket.socket (socket.af_inet, socket. SOCK_STREAM)
# to establish a connection:
S.connect (' m.yintai.com ', 80)

While True:
data = S.RECV (1024)

Getting started with Python-functional programming