Python foundation -- basic data type & STR operation

1. Overview of basic number types (7 Kind of )

   • 10203 123 3340 int +- * / wait
   • ' Did you eat today ？' str Store a small amount of data ,+ *int section , Other methods of operation
   • True False bool Judge true or false
   • [12, True, 'a1', [1,2,3 ]] list Store a lot of data .
   • (12, True, 'a1', [1,2,3 ]) tuple Store a lot of data , You can't change the elements inside .
   • {'name': ' Zhang San '} dict Store a lot of correlated data , Very fast query speed .
   • set intersection , Union difference set ...

2. int

   • Decimal binary conversion

   •  '''
     Binary to decimal
     0001 1010 ------> ? 26
     '''
     b = 1 * 2**4 + 1 * 2**3 + 0 * 2**2 + 1 * 2**1 + 0 * 2**0
     # print(b) # 26
     '''
     42 -----> 0010 1010
     '''
     

   • bit_lenth The effective length of decimal to binary

     # bit_lenth Effective binary length
     i = 4
     print(i.bit_length()) # 3
     i = 5
     print(i.bit_length()) # 3
     i = 42
     print(i.bit_length()) # 4
     

3. bool

   • bool str int The transition between the three

     # bool str int
     # bool <---> int
     '''
     True 1 False 0
     Non zero means True 0 yes False
     '''
     # str <---> int ***
     '''
     s1 = 10 int(s1) : It has to be digital
     i = 100 str(i)
     '''
     # str bool ***
     # It's not empty True
     s1 = ' '
     print(bool(s1)) # True Spaces are also characters
     s1 = '' # An empty string
     print(bool(s1)) # False
     # bool ---> str meaningless
     print(str(True))
     

   • application ：

     s = input(' Input content ')
     if s:
     print(' There are content ')
     else:
     print(' No input ')
     

4. str

   • Index slice step size

     s1 = 'python The whole stack 22 period '
     # Index strings , The sliced data is of string type .
     # Value by index
     # There is an order from left to right , Subscript , Indexes .
     s2 = s1[0]
     print(s2,type(s2))
     s3 = s1[2]
     print(s3)
     s4 = s1[-1]
     print(s4)
     # Value according to slice .
     # I don't care
     s5 = s1[0:6]
     s5 = s1[:6]
     print(s5)
     s6 = s1[6:]
     print(s6)
     # Slice step size
     s7 = s1[:5:2]
     print(s7)
     print(s1[:])
     # In reverse order ：
     s8 = s1[-1:-6:-1]
     print(s8)
     # By index ：s1[index]
     # According to the slice ： s1[start_index: end_index+1]
     # According to the slice step size ： s1[start_index: end_index+1:2]
     # Reverse according to slice step size ： s1[start_index: end_index One bit later :2]
     # Thinking questions ： All in reverse order ？
     

   • Exercises

     2. There are strings s = "123a4b5c"
     Through to s Slice to form a new string s1,s1 = "123"
     Through to s Slice to form a new string s2,s2 = "a4b"
     Through to s Slice to form a new string s3,s3 = "1345"
     Through to s Slice into strings s4,s4 = "2ab"
     Through to s Slice into strings s5,s5 = "c"
     Through to s Slice into strings s6,s6 = "ba2"
     

   • Common operation methods

     # upper lower
     # s1 = s.upper()
     # # s1 = s.lower()
     # print(s1,type(s1))
     # application ：
     username = input(' user name ')
     password = input(' password ')
     code = 'QweA'
     print(code)
     your_code = input(' Please enter the verification code ： Case insensitive ')
     if your_code.upper() == code.upper():
     if username == ' The white ' and password == '123':
     print(' Login successful ')
     else:
     print(' Wrong username and password ')
     else:
     print(' Verification code error ')