Python QuickStart

2020年2月13日 (四) 19:04的版本

1 Quick Start

Install python3.8 from https://www.python.org/downloads/

Install pip:

$ curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
$ sudo python get-pip.py

Using the pip to install the numpy and tensorflow package:

$ sudo pip3 install numpy pandas matplotlib
$ sudo pip3 install tensorflow

2 Basics

2.1 Numbers

Python 2.7.9 (default, Mar  1 2015, 12:57:24) 
>>> a = 3.23
>>> b = 4
>>> c = 52.3E-4
>>> print a, b, c
3.23 4 0.00523

2.2 HEX

>>> print str(254)
254
>>> print hex(254)
0xfe
>>> print hex(254).upper()
0XFE
>>> str = "%02X" %(254); print str
FE
>>> print hex(1023)
0x3ff
>>> print hex(1023)[0:-2]
0x3

2.3 Strings

#!/usr/bin/python

str_1 = 'Jack Tan'
str_2 = "Ga Xiao Duo"
str_3 = '''This is a multi-line string. first line.
second line'''

# using the startswith method of the string object
if str_1.startswith('Ja'):
    print("Yes, str_1 start with 'Ja'")

if 'a' in str_1:
    print('Yes, str_1 contains the string "a"')

substr = 'ac'
if str_1.find(substr) != -1:
    print('Yes, str_1 contains the string "{0}"'.format(substr))
    print('Yes, {0} contains the string "{1}"'.format('str_1', substr))
    print('Yes, {} contains the string "{}"'.format('str_1', substr))
    # using the format method of the string object

deli = '_*_'
mylist = ['Brazil', 'Russia', 'India', 'China']

# using the join method of the string object
print(deli.join(mylist))

Output:

Yes, name start with 'Ja'
Yes, name contains the string "a"
Yes, name contains the string "ac"
Brazil_*_Russia_*_India_*_China

Once your have created a string, you cannot change it

2.4 Variable

Python refers to anything used in a program as an object.

Do not need type declaration of variable in python

Python 2.7.9 (default, Mar  1 2015, 12:57:24) 
>>> a = 3.1415
>>> b = 100000
>>> c = 'Jack Tan'
>>> d = ['x1', 'x2']
>>> print a, b, c, d
3.1415 100000 Jack Tan ['x1', 'x2']

.

Variables can hold values of different types called data types. The basic types are numbers and strings. We can create our own types using classes.

2.5 Indentation

Whitespace at the beginning of the line is important!

Spaces and tabs at the beginning of the logical line are used to determine the indentation level of the logical line, which in turn is used to determine the grouping of statements.

Statements which go together must have the same indentation. Each usch set of statements is called a block

2.6 Format

#!/usr/bin/python

#width = 10,precise = 3,align = left
print "PI = %10.3f" %(math.pi)

# don't add the '\n' at the end of line
print "PI = %10.3f" %(math.pi),

#width = 10,precise = 3,align = rigth
print "PI = %-10.3f" % math.pi

Output:

PI = 3.141593
PI =      3.142

Python 2.7.9 (default, Mar  1 2015, 12:57:24) 
>>> print "%.3s " % ("jcodeer") #precise = 3
jco 
>>> print "%.*s" % (4,"jcodeer") #precise = 4
jcod
>>> print "%10.3s" % ("jcodeer") #width = 10,precise = 3
       jco
>>>

fmat = "%r %r %r %r"
 
print fmat % (1, 2, 3, 4)
print fmat % ("one", "two", "three", "four")
print fmat % (True, False, False, True)

1 2 3 4
'one' 'two' 'three' 'four'
True False False True

print('{0:.3}'.format(0.3333333))
#print('{0:.3}'.format(1/3))
print('{0:_^11}'.format('Hello'))
print('{0:+^11}'.format('Hello'))
print('{name} wrote {book}'.format(name='Jack', book='Hello world'))

PI = 3.141593
PI =      3.142

0.333
___Hello___
+++Hello+++
Jack wrote Hello world

3 Operators

4 Control Flow

4.1 if

i = 5
if i == 0:
    print 'Zero'
elif i > 0:
    print 'Positive'
else:
    print 'Negative'

4.2 While

n = 4
while n:
    print 'Loop is OK'
    n -= 1
else:
    print 'Loop is over'

4.3 For

for ... in

for i in range(1,5):
    print i
else:
    print 'The loop is over'

5 Functions

6 Data Structures

7 Exceptions

7.1 with...as

#!/usr/bin/python

import sys

class test:
    def __enter__(self):
        print("enter")
        return 1
    def __exit__(self, *args):
        print("clean up")
        return False
        #return True


with test() as t:
    print("t is not the result of test(), it's __enter__ returned")
    print("t is 1, yes, it's {0}".format(t))
    print "t is 1, yes, it's", t
    raise NameError("Error")

sys.exit()
print("Never here")

8 Matplotlib

Gallery
Change the Colors Changes to the default style
Demo Fixed Size Axes
Multiple Figs Demo
Usetex Demo
Controlling style of text and labels using a dictionary
matplotlib.pyplot.plot()
matplotlib.pyplot.figure()

8.1 bar

8.2 hist

hist.cdf

9 Modules

9.1 Serial

import serial
import string
import binascii

s = serial.Serial('com4',9600)
s.open()

# rx data
n = s.inwaiting()
if n: 
    data = str(binascii.b2a_hex(s.read(n)))[2:-1]
    print(data)

# tx data
d = bytes.fromhex('10 11 12 34 3f') 
s.write(d)
s.close()

9.2 Struct (TX binary data)

import struct 

a = [0x00, 0x00, 0x00, 0x2c, 0x63, 0x00, 0x00, 0x00,  0x75, 0x4b, 0xef, 0x0f] 

s = socket.socket(socket.AF_INET,socket.SOCK_STREAM) 

s.connect(('127.0.0.1',8000)) 

date = struct.pack("%dB"%(len(a)),*a) 

s.send(date)

9.3 MQTT

Please refer to: http://wiki.jackslab.org/Noduino_OpenPlug#Turn_off_2

9.4 HTTP

httplib 实现了 http & https 的客户端协议，模块 urllib 和 urllib2 对 httplib 进行了更上层的封装

#!/usr/bin/env python
#  -*- coding:utf-8 -*-
 
import urllib2
import json
 
def http_post(url,data_json):
    jdata = json.dumps(data_json)
    req = urllib2.Request(url, jdata)
    response = urllib2.urlopen(req)
    return response.read()
 
url = 'http://192.168.0.100:8080/dev/test'
data_json = {'data' : '112233'}
resp = http_post(url,  data_json)
print(resp)

使用post方式时，数据放在 data 或者 body 中：

import urllib
import urllib2

test_data = {'ServiceCode':'aaaa','b':'bbbbb'}
test_data_urlencode = urllib.urlencode(test_data)
requrl = "http://192.168.1.16/dev/test"
req = urllib2.Request(url = requrl, data =test_data_urlencode)
print req
res_data = urllib2.urlopen(req)
res = res_data.read()
print res

Reference: https://blog.csdn.net/lovemysea/article/details/77776299

9.5 Time

10 Resource

Online Python: http://www.compileonline.com/execute_python_online.php

Python Quick Start: http://www.tutorialspoint.com/python/python_lists.htm

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