python note #2

This passage will talk about some small but pretty important knowledge points, including using method of string, tuple, dictionary and some specific examples.

Part 1: Import a Program

1. import sys:

 import sys
 print (sys.path) # 打印环境变量
 print(sys.argv)
 # Sys.argv[ ]其实就是一个列表，里边的项为用户输入的参数，
 # 这参数是从程序外部输入的，而非代码本身的什么地方，要想看
 # 到它的效果就应该将程序保存了，从外部来运行程序并给出参数。
 print(sys.argv[2])

import sys

2. import os:

 # os用于系统交互，调用系统路径等
 import os
 # cmd_res = os.system('dir') # 只执行命令，不保存结果，系统交互
 cmd_res = os.popen('dir').read()
 print('---->',cmd_res)
 os.mkdir('new_dir')

import os

3. import a file from other directory

　　use (import file_name) directly. And this knowledge point shows how the python file imported work.

 '''
 .pyc中，c = compile
 命令行中输入python hello.py ---> （系统编译）--->激活解释器
 python编译器结果 --> 内存中PyCodeObject --> 程序结束，PyCodeObject写回到.pyc文件中
 再次运行时，直接读取.pyc，避免重复过程
 即.pyc是PyCodeObject的永久保存文件
 '''

knowledge point

　example 1:

　　step1: create a file for importing and save it into 'D:\Python\Lib\site-packages'

　　　　　

 # Author: Eva Han

 import getpass

 _username = 'eva'
 _password = ''
 username = input("username:")
 password = input("password:")

 if _username == username and _password == password:
     print("welcome {name} to my world!".format(name=username))
 else:
     print("invalid information!!!")

 print(_username,_password)

password

　　step2: import file_name

　　　　import password

4. the type of data

　　1) number

　　　　int　　eg: 1, 2, 3

　　　　float　　eg: 3.23, 3E-6

　　　　complex　　eg: -5+4j

　　2) bull

　　　　1 ---> True　　0 ---> False

　　3) string

　　　　eg: 'Hello World!'

　　4) types of bytes

　　　　　　　　　　encode

　　　　string ---------------------------------> bytes

　　　　　　   <--------------------------------

　　　　　　　　　　decode

　　　　　eg: '$20'.encode('utf-8')　　　

　　　　　　

 msg = '我爱python！'
 print(msg.encode('utf-8'))
 print(msg.encode('utf-8').decode('utf-8'))

encode & decode

5. triple operation & systems

 '''
 三元运算 triple operation
     result = 值1 if 条件 else 值2
 进制 system
     十六进制与二进制 （取四合一）
     0     /1     /2     /3     /4     /5     /6     /7     /8     /9
     0000  0001   0010   0011   0100   0101   0110   0111   1000   1001

     A     /B     /C     /E     /F
     1010  1011   1101   1110   1111
     十六进制
         H ---> 后缀 BH表示的是B
         0X ---> 前缀 0X53表示的是53
         补位 ---> 以小数点为分割线，向左向右取四位后进行补位
             eg：10111.011 ---> 0001 、 0111 、 0110

 '''

knowledge point

Part 2: List

function: save all users' name into a list and use it

 # Author: Eva Han
 import copy
 '''
 功能：将所有人的名字存成列表并调用
 新数据类型：列表
 '''

 names = ['Peggi', 'Georgia', 'Peggi_Pappa',['Eva','Katrina'], 'Peggi_Mom']

 # 按步长切片
 print(names[0:-1:2])
 print(names[::2])
 print(names[:])

 # 列表内容循环
 for i in names:
     print(i)

 '''
 # 浅copy只copy第一层-创造联合账号，深copy可以copy到所有
 name2 = names.copy()
 name3 = copy.copy(names)
 name5 = list(person)  # 浅copy
 name4 = copy.deepcopy(names)
 names[3][1] = '0000'
 print(names)
 print(name2)
 print(name3)
 print(name4)
 '''

 '''
 # 附加与插入
 names.append('Peggi_Grandpa')
 names.insert(1,'Peggi_Grandma')
 print(names)

 # 改与删
 names[2] = 'new name'
 names.remove('Peggi')
 del names[0] # 与names.pop(0)相同
 names.pop() # 默认删除最后一个值
 print(names)

 print(names[0], names[2])
 # 切片：从1位置取到3位置,起始位置包括，终止位置不包括
 print(names[1:3])
 # 取最后一个的值
 print(names [-1])
 print(names[-3:])
 # 可以忽略0

 # 输出位置
 print(names[names.index('Peggi_Pappa')])
 # count_统计数目，clear_清空列表，reverse_列表顺序反转
 # sort_按特殊符号-数字-大写字母-小写字母顺序排序

 print(names)
 names2 = [1,2,3,4]
 names.extend(names2)
 print(names)
 '''

list

Notice!!! The logic about assigning a value between string, number and lists is pretty different.

example 2:

　　1) string and number

　　　　a = 1 ---> b = a ---> a = 555 ---> b = 1

　　2) list

　　　　a = [1, 2, 3] ---> b=a ---> a[1] = 555 ---> b = [1, 555, 3]

Part 3: Tuple

The Tuple can only be read, and cannot be revised.

 # Author: Eva Han

 # 元组 = 只读列表
 names = ('Eva','Anna','Nancy','Georgia','Nancy')
 print(names.index('Georgia'))
 print(names.count('Nancy'))

tuple

Part 4: String

All commands may be included in the string.

 # Author: Eva Han

 name = 'my \t{name} is {Eva} Han'

 # 首字母大写
 print(name.capitalize())
 # 计数字母
 print(name.count('n'))
 # 公输入50个字符，不满的用-填满
 print(name.center(50,'-'))
 # encode,discode
 # endwith_以...结尾
 print(name.endswith('ex'))
 # 将tab键制定扩成空格
 print(name.expandtabs(tabsize=20))
 # 查找位置，进行切片
 print(name[name.find('name'):])
 # format进行格式化,format_map用于字典
 print(name.format(name='kkk',Eva='qqq'))
 print(name.format_map( {'name':'kkk','Eva':'qqq'} ))
 # isalnum—是否是阿拉伯数字和字母
 # isalpha-是否是英文（大写、小写）字母
 # isdecimal-是否是十进制
 # isdigit-是否是整数
 # isidentifier-判断是不是一个合法的标识符、变量名
 # islower - 是不是小写
 # isnumeric - 判断是不是纯数字
 # isspace - 是不是空格
 # istitle - 每个首字母大写
 # isprintable - 设备终端需要，ttf file/ drive file
 # isupper - 是否全是大写
 # join - 连接
 print('ab_23'.isalnum())
 print('+'.join(['','','','']))
 # 左加*，右加*
 print(name.ljust(50,'*'))
 print(name.rjust(50,'*'))
 # lower - 大写变小写
 print('EVA'.lower())
 print('eva'.upper())
 # 从左边去掉空格与回车,\n换行
 print('  Eva  '.lstrip())
 print('  Eva  '.rstrip())
 print('  Eva  '.strip())
 # 加密，对应转换，随机密码
 p = str.maketrans('abcdef','')
 print('Eva Han'.translate(p))

 print('Eva'.replace('a','A',1)) # 替换第一个a
 print('eva han'.rfind('h')) # 返回最后面的值
 print('1+2+3+4+5+6'.split('+')) # 把字符串按--分成列表
 print('1+2\n+3+4'.splitlines()) # 按换行符来存
 print('Eva Han'.swapcase()) # 大小写互换
 print('eva han'.title()) # 标题首字母大写
 print('eva han'.zfill(50)) # 不够的用0填空

string

Part 5: Dictionary

 # Author: Eva Han
 # 字典，索引表来查对应页的详细信息，key-value

 info = {
     '':'Eva Han',
     '':'Nancy Tang',
     '':'Katrina Yue',
 }

 print(info)
 # print(info['2014110543'])
 info[''] = '卡翠娜·岳'
 info[''] = 'Dream High'
 print(info)
 # 获取数据
 print(info.get(''))
 print('' in info)

 # #del info['2014110543']
 # info.pop('2014110543')
 # #随机删除
 # # info.popitem()
 # print(info)

 # # 多级嵌套
 website_collection = {
     'search': {
         'www.baidu.com':['most popular in China','use it when you are in China'],
         'www.google.com':['popular around the world','best use, clean and convenient'],
         'www.yahoo.com':['rarely use it','also needs vpn?']
     },
     'video':{
         'www.aiqiyi.com':['BBC videos included','net video included'],
         'www.bilibili.com':['otaku best love','nya my love!'],
         'www.tencent.com':['just soso','cheap for students'],
     },
     'music':{
         'www.wangyinetmusic.com':['good music list','good quality'],
         'kugou_music':['emmmmmmmmmmmmm','cheap vip?'],
         'kuwo_music':['memories','just soso'],
     },
 }

 # 替换
 website_collection['video']['www.bilibili.com'][1]='you like it!'
 # 有值返回，无值增加
 website_collection.setdefault('study',{'English':['new orientation','famous']})
 print(website_collection)

 # update: 合并字典，有交叉更新，无交叉覆盖
 b = {1:2,3:4,'':'Tang Fan'}
 info.update(b)
 print(info)

 # items 字典变列表
 print(info.items())

 # fromkeys 初始化字典,三个key共享一个地址
 c = dict.fromkeys([6,7,8],'test')
 print(c)

 # 字典循环
 for i in info:
     print(i,info[i])

 # 这种没有上一种高效
 for k,v in info.items():
     print(k,v)

dictionary

example 3: three-level menu

 # Author: Eva Han

 location = {
     'sichuan':{
         'chengdu':{ 'jinniu','xipu', 'qingyang'},
         'mianyang':{'youxian','anzhou'},
         'beichuan':{'dongcheng','xicheng','beicheng'}
     },
     'chongqing':{
         'wanzhou':{'zhuxiang','jiuchi'},
         'changshou':{111,222,333},
         'banan':{000,444,555},
     },
     'Yunnan':{
         'kunming':{147,258,369},
         'yuxi':{753,951,456},
         'lijiang':{777,888,999},
     },
 }
 exit_flag = False

 while not exit_flag:
     for i in location:
         print(i)
     choice1 = input('>>choose province:')
     if choice1 in location:
         while not exit_flag:
             for j in location[choice1]:
                 print('\t',j)
             choice2 = input('>>choose city:')
             if choice2 in location[choice1]:
                 while not exit_flag:
                     for k in location[choice1][choice2]:
                         print('\t\t',k)
                     choice3 = input('>>choose district,final level, press b to go back, press q to quit:')
                     if choice3 == 'b':
                             break
                     elif choice3 == 'q':
                             exit_flag = True
             if choice2 == 'b':
                 break
             elif choice2 == 'q':
                 exit_flag = True

 # 字典中按值返回，列表中按位置返回

3-level menu