Python基础day-2[流程控制,字符串操作]
流程控制:
if 语句:
if 条件1： （缩进四个空格）条件1成立的话执行的命令 elif条件2: 前面的条件不成立执行这个语句 else: 之前的所有条件均不成立的情况下执行的命令 print('1') //这个print不属于 if判断中
while语句:
//登录用户输入命令 tag = True //设置标签 while tag : user = input('Please enter your username:') //等待用户输入 passwd = input('Please enter your password:') if user == 'abc' and passwd == '123': //判断用户输入 while tag : //子循环 cmd = input('Please enter command:') //等待用户输入命令 if cmd == 'exit': //如果输入exit tag = False //执行 tag = False continue //跳出本层循环 print(cmd) //打印出用户输入的命令
for语句:
for x in range(4): //循环给 x赋值 范围 #0 1 2 3 //range函数 顾头不顾尾 range(1,5) # 1 2 3 4 步长:range(1,5,2) #1 3 print('=====>',x) #九九乘法表 for x in range(1,10): //控制行 for y in range(1,x+1): print('%s*%s=%s'%(x,y,x*y),end = ' ') //end= ' ' 打印不换行 print() //循环完一次换行
数据类型:
进制:
bin():换算十进制为二进制
oct():换算十进制为八进制
hex():换算十进制为十六进制
数字类型的特点:
1.只能存放一个值
2.一经定义不能更改
3.可直接访问
字符串的类型:
只要是引号中的都是字符串,单引号双引号在Python中没有区别.
s='hello world' s1="hello world" s2="""hello world""" s3='''hello world''' print(type(s)) print(type(s1)) print(type(s2)) print(type(s3)) D:\Python\Python36-32\python.exe #运行结果 <class 'str'> <class 'str'> <class 'str'> <class 'str'> Process finished with exit code 0
字符串的常用操作:
x.strip()
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py username:*************a***********b********c************ a***********b********c Process finished with exit code 0
x.capitalize() #首字母大写
x='hello'
x = x.capitalize()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
Hello
Process finished with exit code 0
x.upper() #字母全部大写
x='hello'
x = x.upper()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
HELLO
Process finished with exit code 0
x.lower() #字母全部小写
x = 'HELLO'
x = x.lower()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
hello
Process finished with exit code 0
x.center() #设置字符宽度居中显示
x = 'HELLO'
x = x.center(20,'=') #括号内设置字符宽度为20,填充字符为'='
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py =======HELLO======== Process finished with exit code 0
x.count() #计数,统计字符串中某一字符的个数
x = 'HELLO,Hello,hello' #字符从左到右,索引位置分别是:0,1,2,3,4..... 其中空格和标点符号均算做一个字符.
# x = x.count('e') #统计字符串中'e'有几个
x = x.count('e',0,10) #统计字符串中'e'有几个,统计范围0-10个字符
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py 1 Process finished with exit code 0
x.endswith() #从字符串尾部开始判断,是否是相应的值
x = 'HELLO,Hello,hello ' #尾部有个空格
x = x.endswith(' ') #判断是否以空格结尾
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
True
Process finished with exit code 0
x.startswith() #从字符串头部判断,是否是相应的值
x = 'HELLO,Hello,hello '
x = x.startswith('HELLO')
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
True
Process finished with exit code 0
x.find() #查找字符,如果有就显示找到的第一个字符的索引位置,如果没有就返回一个负数
x = 'HELLO,Hello,hello'
x = x.find('e')
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py 7 Process finished with exit code 0
x.format() #格式化字符串
x = 'Name:{},age:{},sex:{}' #定义一串字符串
x = x.format('abc',18,'male') #数值会依次跟上面的大括号对应
print(x)
x = 'Name:{0},age:{1},sex:{0}' #使用数据位置
x = x.format('aaaaaaaaaaaaaaaaa','bbbbbbbbbbbbbb')
print(x)
x = 'Name:{x},age:{y},sex:{z}' #直接定义括号内的数值,这种方式 format中的数值可以使无序的
x = x.format(y=18,x='abc',z='male')
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py Name:abc,age:18,sex:male Name:aaaaaaaaaaaaaaaaa,age:bbbbbbbbbbbbbb,sex:aaaaaaaaaaaaaaaaa Name:abc,age:18,sex:male Process finished with exit code 0
x[] #取出字符串对应索引位置的字符,也可以输入 负数从字符串尾部开始计算位置.
x = 'Hello python'
x = x[1]
print(x)
x = 'Hello python'
x = x[5]
print(x)
x = 'Hello python'
x = x[0]
print(x)
x = 'Hello python'
x = x[10]
print(x)
补充:
>>> x = 'Hello python'
>>> x[1:5]
'ello'
>>> x[1:5:2]
'el'
>>> x[0:5:2]
'Hlo'
>>>
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
e
H
o
Process finished with exit code 0
x.index() #输出字符的索引位置,如果有多个相同字符则只输出第一个找到的
x = 'Hello python'
x = x.index('o')
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py 4 Process finished with exit code 0
x.isdigit() #判断是否是数字
x = 'Hello python'
x = x.isdigit()
print(x)
x = '1231231'
x = x.isdigit()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
False
True
Process finished with exit code 0
x.replace() #替换字符
x = 'Hello python'
x = x.replace('Hello','Hi')
print(x)
x = 'Hello python Hello'
x = x.replace('Hello','Hi',2) #括号内的数字代表替换几次,不设定默认只替换找到的第一个
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
Hi python
Hi python Hi
Process finished with exit code 0
x.split() #以什么为分隔符分割字符串
x = 'Hello python Hello'
x = x.split() #不指定,以空格为分隔符进行分割
print(x)
x = 'aa*bb*c'
x = x.split('*') #指定以'*'号为分隔符进行分割
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py ['Hello', 'python', 'Hello'] ['aa', 'bb', 'c'] Process finished with exit code 0
x.isupper() #判断字符串是否是大写
x = 'hello'
x = x.isupper()
print(x)
x = 'HELLO'
x = x.isupper()
print(x)
x = 'Hello'
x = x.isupper()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
False
True
False
Process finished with exit code 0
x.islower() #判断字符串是否是小写
x = 'hello'
x = x.islower()
print(x)
x = 'HELLO'
x = x.islower()
print(x)
x = 'hEllo'
x = x.islower()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
True
False
False
Process finished with exit code 0
x.isspace() #判断字符串是否为空格
x = 'hello'
x = x.isspace()
print(x)
x = ' '
x = x.isspace()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
False
True
Process finished with exit code 0
x.istitle() #判断是否是标题,有点像判断首字母是否大写
x = 'hEllo'
x = x.istitle()
print(x)
x = 'Hello'
x = x.istitle()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
False
True
Process finished with exit code 0
x.title() #把字符串转换为标题
x = 'hEllo'
x = x.title()
print(x)
x = 'hEllO'
x = x.title()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
Hello
Hello
Process finished with exit code 0
x.swapcase() #转换大小写
x = 'hEllo'
x = x.swapcase()
print(x)
x = 'Hello'
x = x.swapcase()
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py HeLLO hELLO Process finished with exit code 0
x.ljust() #左对齐
x.rjust() #右对齐
x = 'hEllo'
x = x.ljust(10,'=')
print(x)
x = 'abc'
x = x.rjust(10)
print(x)
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py hEllo===== abc Process finished with exit code 0
针对上面的内容补充:
1.x = x.xxxx()
print(x)
这种写法也可以这么写:print(x = x.xxxx()),向下面这种示例.
x='abc'
print(x.ljust(10,'*'))
print(x.rjust(10,'*'))
2.当我们在Python中设置字符串变量时:x = 'abc' 其实就是执行了 : x = str('abc')
3.设置变量的时候:a = 1 这时在python中记录的就是 int型数据,a = 'abc' 系统记录的就是 str型数据,只有在 设置input 等待用户输入的数据才会被一律视为 str.
4.计算字符长度可以使用len(),计数是从1开始计数.字符串索引是从0开始计数.如下示例:
msg='hello egon 666' print(len(msg)) #使用len计算出msg的字符数为14 for n in range(14): #使用range函数生成0-13 print(msg[n],end = ' ') #循环打印出索引位置字符,不换行输出
D:\Python\Python36-32\python.exe E:/Python/作业/day2.py
14
h e l l o e g o n 6 6 6
Process finished with exit code 0
5.2017/06/07 Python练习
#1：编写for循环，利用索引遍历出每一个字符 # msg='hello egon 666' # print(len(msg)) # for n in range(14): # print(msg[n],end = ' ') #2：编写while循环，利用索引遍历出每一个字符 # msg='hello egon 666' # n = 0 # while n < 14: # print(msg[n],end = ' ') # n += 1 #3:msg='hello alex'中的alex替换成SB # msg='hello alex' # print(msg.replace('alex','SB')) #4:msg='/etc/a.txt|365|get' 将该字符的文件名，文件大小，操作方法切割出来 # msg='/etc/a.txt|365|get' # s1 = msg.split('|') # print(s1) # print('文件名是{},文件大小是{},操作方法是{}'.format(*s1)) # print('文件名是%s,文件大小是%s,操作方法是%s'%tuple(s1)) #5.编写while循环，要求用户输入命令，如果命令为空，则继续输入 # tag = True # while tag: # cmd = input('Please enter command: ') # if cmd == '': # continue # else: # print(cmd) # tag = False #6.编写while循环，让用户输入用户名和密码，如果用户为空或者数字，则重新输入 # tag = True # while tag: # user = input('Please enter your username:') # passwd = input('Please enter your password:') # if user == '' and passwd == '': # continue # elif user == 'abc' and passwd == '123': # print('login successful') # tag = False # else: # print('login fail') # tag = False #7.编写while循环，让用户输入内容，判断输入的内容以alex开头的，则将该字符串加上_SB结尾 # while True: # name = input('Please enter your name:') # if name.startswith('alex'): # print(name,'SB') # break # else: # print('hello',name) #8.下列要求: #1.两层while循环，外层的while循环，让用户输入用户名、密码、工作了几个月、每月的工资（整数），用户名或密码为空，或者工作的月数不为整数，或者 #月工资不为整数，则重新输入 #2.认证成功，进入下一层while循环，打印命令提示，有查询总工资，查询用户身份（如果用户名为alex则打印super user，如果用户名为yuanhao或者wupeiqi #则打印normal user，其余情况均打印unkown user），退出功能 #3.要求用户输入退出，则退出所有循环（使用tag的方式） # # tag = True # while tag: # user = input('请输入用户名:') # passwd = input('密码:') # work_mons = input('工作了几个月?:') # salary = input('请输入你每月的工资(整数):') # if user == '' or passwd == '' or work_mons.isdigit() != True or salary.isdigit() != True: # print('输入数据错误,请重新输入.') # continue # else: # print('登录成功') # while tag: # print(''' # 1.查询总工资 # 2.查询用户身份 # 3.退出登录 # ''') # n = input('>>:') # if n == '1': # # work_mons = int(work_mons) # # salary = int(salary) # #money = int(work_mons) * int(salary) # #print('你的总工资是:',money) # print('你的总工资是:',int(work_mons) * int(salary)) # elif n == '2' and user == 'alex': # print('super user') # elif n == '2' and (user == 'yuanhao' or user == 'wupeiqi'): # print('normal user') # elif n == '2': # print('unknow user') # elif n == '3': # tag = False
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