python-for循環-數字類型-字元串類型str

文章目錄

• • • 一、for循環
    • 二、數字類型
    • 三、字元串類型str

一、for循環

while循環 vs for 循環

while循環：稱之為條件循環，循環的次數取決于條件何時為False

for循環：稱之為疊代循環，循環的次數取決于資料的包含的元素的個數

for循環專用來取值，在循環取值方面比while循環要強大，以後但凡遇到循環取值的場景，就應該用for循環

l=['a','b','c']
for i in range(3):
    print(i,l[i])

           

#for+break
names=['egon','kevin','alex','hulaoshi']
for name in names:
    if name == 'alex':break
    print(name)

           

#for+continue
names=['egon','kevin','alex','hulaoshi']
for name in names:
    if name == 'alex':continue
    print(name)
           

#for+else
names=['egon','kevin','alex','hulaoshi']
for name in names:
    print(name)
else:
    print('=====>')

           

#for循環嵌套
for i in range(3):
    for j in range(2):
        print(i,j)
"""
外層循環第一次：i=0
	内層循環
	0，0
	0，1
外層循環第二次：i=1
	内層循環
	1，0
	1，1
外層循環第三次：i=2
	内層循環
	2，0
	2，1
	
"""
           

二、數字類型

1. 整型int

   用途：記錄年齡、等級、号碼等

   定義方式：

   類型轉換

   print(int(3.1)) #結果3
   res = (int('11'))
   print(res,type(res)) #結果11，類型int
   
   res = (float('11.1'))
   print(res,type(res)) #結果11.1，類型float
   
              

   了解

   print(bin(12)) #10進制轉2進制
   print(oct(12)) #10進制轉8進制
   print(hex(12)) #10進制轉16進制
              

   存一個值，不可變

   #不可變
   x = 10
   print(id(x)) #id為1654681344
   x = 11
   print(id(x)) #id為1654681376
   
              

2. 浮點型float

   用途：記錄身高、體重、薪資等

   定義方式

   類型轉換

   print(float(10)) #結果為10.0
   print(float(1.1)) #結果為1.1
   print(float('1.1')) #結果為1.1
              

   存一個值，不可變

   #不可變
   x = 10.3
   print(id(x)) #id為2114155192440
   x = 11.2
   print(id(x)) #id為2114155192512
   
              

三、字元串類型str

1. 用途：記錄描述型值的狀态，比如名字、性别等

2. 定義方式

   類型轉換：可以把任意類型轉成字元串類型

   res1 = str(10)
   res2 = str(10.3)
   res3 = str([1, 2, 3])
   res4 = str({'x': 1})
   print(type(res1))
   print(type(res2))
   print(type(res3))
   print(type(res4))
              

3. 常用操作+内置方法

   ​ 優先掌握的操作

   1. 按索引取值(正向取+反向取) 隻能取

      msg = 'hello world'
      print(msg[0]) #h
      print(msg[-1]) #d
                 

   2. 切片(顧頭不顧尾，步長)

      msg = 'hello world'
      print(msg[0:5]) #hello
      print(msg[0:5:2]) #hlo
      print(msg[0:]) #hello world
      print(msg[:]) #hello world
      print(msg[-1:-5:-1]) #dlro
      print(msg[::-1]) #dlrow olleh
                 

   3. 長度len：統計的是字元的個數

      msg = 'hello world'
      print(len(msg)) #11
      
                 

   4. 成員運算in和not in：判斷一個子字元串是否存在與一個大字元串中

      msg = 'hello world'
      print('ho' in msg) #False
      print('ho' not in msg) #True
                 

   5. 移除空白strip：移除字元串左右兩邊的某些字元串

      msg = '      hello      '
      print(msg.strip())
      
      msg = '***h**ello**********'
      print(msg.strip('*')) #h**ello
      
      msg = '*-=+h/ello*(_+__'
      print(msg.strip('*-=+/(_')) #h/ello
      
      #示範
      name = input('name>>>: ').strip()
      pwd = input('password>>>: ').strip()
      if name == 'egon' and pwd == '123':
          print('login successfull')
      else:
          print('username or password error')
                 

   6. 切片split:把有規律的字元串切成清單進而友善取值

      info = 'egon:18:180:150'
      res = info.split(':', 1) #1代表切分機次
      print(res) #['egon', '18:180:150']
      print(res[1]) #18:180:150
      
      info = 'egon:18:180:150'
      res = info.split(':')
      print(res) #['egon', '18', '180', '150']
      
      
      info = 'egon:18:180:150'
      res = info.split(':')
      s1=''
      for item in res:
          s1+=item
      print(s1) #egon18180150
      
      info = 'egon:18:180:150'
      res = info.split(':')
      s1 = ':'.join(res)
      print(s1) # egon:18:180:150
      
                 

   7. 循環

      for i in 'hello':
          print(i)
                 

​ 需要掌握的操作

1. strip,lstrip,rstrip

   msg = '*****hello****'
   print(msg.strip('*')) #hello
   print(msg.lstrip('*')) #hello****
   print(msg.rstrip('*')) #*****hello
              

2. lower,upper

   msg = 'AaBbCc123123123'
   print(msg.lower()) #aabbcc123123123
   print(msg.upper()) #AABBCC123123123
              

3. startswith,endswith

   msg = 'alex is dsb'
   print(msg.startswith('alex')) #True
   print(msg.endswith('sb')) #True
              

4. format的三種玩法

   msg = 'my name is {name} my age is {age}'.format(age=18, name='egon')
   print(msg) #my name is egon my age is 18
   
   msg = 'my name is {} my age is {}'.format(18, 'egon')
   print(msg) #my name is 18 my age is egon
   
   msg = 'my name is {0}{0} my age is {1}{1}{1}'.format(18, 'egon')
   print(msg) #my name is 1818 my age is egonegonegon
   
              

5. split,rsplit

   cmd = 'get|a.txt|33333'
   print(cmd.split('|', 1)) #['get', 'a.txt|33333']
   print(cmd.rsplit('|', 1)) #['get|a.txt', '33333']
              

6. replace

   msg = 'kevin is sb kevin kevin'
   print(msg.replace('kevin', 'sb', 2)) #sb is sb sb kevin
              

7. isdigit #當字元串内為純數字時結果為True

   res = '11111'
   print(res.isdigit())
   int(res) #True
   
   #示範
   age_of_bk = 18
   inp_age = input('your age: ').strip()
   if inp_age.isdigit():
       inp_age = int(inp_age)
       if inp_age > 18:
           print('too big')
       elif inp_age < 18:
           print('to small')
       else:
           print('you got it')
   else:
       print('必須輸入純數字')
              

   了解
   1. find,rfind,index,rindex,count

      print('xxxkevin is sb kevin'.find('kevin')) #3
      print('xxxkevin is sb kevin'.index('kevin')) #3
      print('xxxkevin is sb kevin'.rfind('kevin')) #15
      print('xxxkevin is sb kevin'.rindex('kevin')) #15
      
      res = 'xxxkevin is sb kevin'.find('kevasdfsadfin')
      print(res) #-1 表示沒找到
      res = 'xxxkevin is sb kevin'.index('kevasdfsadfin')
      print(res) #沒找到會報錯
      
      print('kevin is kevin is kevin is sb'.count('kevin')) #3次
                 

   2. center,ljust,rjust,zfill

      print('egon'.center(10,'*')) #***egon***
      print('egon'.ljust(10,'*')) #egon******
      print('egon'.rjust(10,'*')) #******egon
      print('egon'.zfill(10)) #000000egon
      
                 

   3. captalize,swapcase,title

      print('my name is kevin'.capitalize()) #My name is kevin
      print('AaBbCc'.swapcase()) #aAbBcC
      print('my name is kevin'.title()) #My Name Is Kevin
                 

   4. is其他

      name = 'egon123'
      print(name.isalnum())  # True 字元串由字母或數字組成
      print(name.isalpha())  # False 字元串隻由字母組成
      print(name.islower()) #True
      print(name.isupper()) #False
      
      name = '    '
      print(name.isspace()) #True
      
      msg = 'I Am Egon'
      print(msg.istitle()) #True