Python基础一

一、变量

声明变量

name = 'kevin'

上述代码声明了一个变量，变量名为： name，变量name的值为：'kevin'

变量定义的规则：

• 变量名只能是 字母、数字或下划线的任意组合
• 变量名的第一个字符不能是数字
• 以下关键字不能声明为变量名
  ['and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'exec', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'not', 'or', 'pass', 'print', 'raise', 'return', 'try', 'while', 'with', 'yield']

#变量是存东西的，存到内存里，给其它调用，由数字字母或者下划线表示，首字母不能为数字
name = "Kevin Zou"
print("My name is ",name)
name2 = name
print(name,name2)
name = "test"
print(name)

gf_of_kevin = 'cc'  #注意命名规范，不要用单个字母，拼音，中文
print(gf_of_kevin)

PIE = 3.14    #常量
print(PIE)

#当行注释
#''' '''多行注释或者打印多行
msg = ''' hello
test'''
print(msg)

 

二、字符编码

python解释器在加载 .py 文件中的代码时，会对内容进行编码（默认ascill）

ASCII（American Standard Code for Information Interchange，美国标准信息交换代码）是基于拉丁字母的一套电脑编码系统，主要用于显示现代英语和其他西欧语言，其最多只能用 8 位来表示（一个字节），即：2**8 = 256-1，所以，ASCII码最多只能表示 255 个符号。

一个字符在ascii码占用一个字节，占8位，在unicode占2个或者2个以上字节
ASCII 255 1bytes （字节）
    -->> 1980 gb2312  7445个 -->>1995 GBK1.0 21866 -->>2000 GB18030 27484
        -->> unicode 一个字符至少2个字节  -->>UTF-8 ascii码中的内容用1个字节保存、欧洲的字符用2个字节保存，东亚的字符用3个字节保存

python3.X默认采用utf-8

三、用户输入

输入密码时，如果想要不可见，需要利用getpass 模块中的 getpass方法，即：

import getpass
username = input("username:")
password = getpass.getpass("password:")
print(username,password)

三种格式化输出：

#Author:Kevin Zou

#输入
'''
username = input("username:")
password = input("password:")
print(username,password)
'''

#python2.x raw_input 等同于python3.x input,python2.x input代表你输入什么格式就是什么格式
name = input("name:")
#age = input("age:")
age = int (input("age:"))   #int()string类型转化成int类型,str() 转化为string类型
#print(type(age))
job = input("job:")
salary = input("salary:")

#格式化输出 1 ：字符串拼接用+,不建议使用,在内存里占用空间大
#info1 = ''' ------info of ''' + name + '''-----
#name:''' + name + '''
#age:'''+ age + '''
#job:''' + job + '''
#salary:''' + salary

#格式化输出 2：s:字符串 d:数字 f:浮点 d/f可以帮助检测验证数据类型
#info ='''------info of %s-------
#Name:%s
#Age:%d
#Job:%s
#Salary:%s''' % (name,name,age,job,salary)

#格式化输出 3：{} .format
info = '''----info of {_name}----
Name:{_name}
Age:{_age}
Job:{_job}
Salary:{_salary}'''.format(_name = name,_age = age,_job = job,_salary = salary)

#另一个写法
info2 = info = '''----info of {0}----
Name:{0}
Age:{1}
Job:{2}
Salary:{3}'''.format(name,age,job,salary)

print(info2)

 

四、if ... else示例

#Author:Kevin Zou
kevin_age = 28
count = 0
while count < 3:
    guess_age = int(input("Guess age:"))
    if guess_age == kevin_age:
        print("You get it,kevin's age is",guess_age)
        break                  #break跳出循环；continue跳出当前循环，继续执行下一个循环
    elif guess_age < kevin_age:
        print("Guess wrong,think bigger...")
    else:
        print("Guess wrong,think smaller...")
    count += 1
    if count == 3:
        continue_guess = input("do you want to continue guess ?")
        if continue_guess != 'n':      
            count = 0
#else:                        #当while 循环全部执行后才执行else语句
   # print("fuck,you guess many times")

 

五、循环

while示例

#Author:Kevin Zou
age_of_kevin = 27
count = 0
'''
while True:
    if count == 100:
        print("ok,count is ",count)
        break
     print("count:",count)
    count = count + 1   #等同于 count += 1
'''

'''
while count < 3:
    print("count:",count)
    count += 1
'''
#while esle 写法
while count < 3:
    guess_age = int(input("guess age:"))
    if guess_age == age_of_kevin:
        print("yes,you get it,kevin's age is %s" % (guess_age))
        break
    elif guess_age > age_of_kevin:
        print("No, you guess error.Think smaller...")
    else:
        print('No,you guess error.Think bigger...')
    count = count + 1
else:
    print("bye! you have no choice!")

for示例

#Author:Kevin Zou

for i in range(3):
    print("loop ",i)
for i in range(0,5,2):
    print("loop ",i)

'''
age_of_kevin = 27
for i in range(3):
    guess_age = int(input("guess age:"))
    if guess_age == age_of_kevin:
        print("yes,you get it,kevin's age is %s" % (guess_age))
        break
    elif guess_age > age_of_kevin:
        print("No, you guess error.Think smaller...")
    else:
        print('No,you guess error.Think bigger...')
else:
    print("bye! you have no choice!")
'''

 

练习：

编写登陆接口

输入用户名密码，先判断用户名是否在lock.txt，如果存在输出锁定信息，如果不存在继续执行。
判断是否成功，从userinfo文件(kevin　　123456)中读取用户密码进行判断，认证成功后显示欢迎信息
输错三次后锁定，将用户名保存到lock.txt文件

#Author:Kevin Zou
tag = 0
count = 0
while count < 3:
    username = input("请输入用户名：")
    password = input("请输入密码：")

    with open('lock.txt','r') as f_lock_read:
        for line in f_lock_read.readlines():
            line = line.strip('\n')
            user = line.split('\t')[0]
            if username == user:
                print("you are locked!")
                tag = 1
    if tag == 1:
        break

    with open('userinfo.txt','r') as f_user_read:
        for line in f_user_read.readlines():
            line = line.strip('\n')
            user = line.split('\t')[0]
            pwd = line.split('\t')[1]
            if username == user and password == pwd:
                print("Welcome %s ,you login successful!" % (username))
                tag = 1
                break
        else:
            print("login failed!")
    if tag == 1:
        break
    count = count + 1
else:
    with open('lock.txt','w') as f_lock_write:
        f_lock_write.write(username)