coercion

Each data type in python has a corresponding method that can convert the data type

Without further ado, let's take a picture:

• str() can convert all other data types to string types

  f_num =  3.1415 
  print ( str ( f_num ) )
  

  • 1
  • 2
• When int() converts a string to a number type, if the string is a pure number, it can be converted

  f_num =  3.1415 
  str_num =  "213" 
  print ( int ( str_num ) ) 
  print ( int ( f_num ) ) 
  '''
  213
  3
  '''
  

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • The container type cannot be converted to a numeric int type
• float() The conversion of floating point type is the same as that of int type, but the result of the conversion is a floating point type
• bool() can convert other types to True or False of boolean type
  • '',0,0.0,False,[],{},(),set()The result of converting to bool in these cases is False
• list() list
  • Number types are non-container types and cannot be converted to lists
  • Converting a string to a list treats each character in the string as an element of the list

    str_num =  "213" 
    print ( list ( str_num ) ) 
    #['2', '1', '3']
    

    • 1
    • 2
    • 3
  • Collection can be converted to list type
  • Tuples can be converted to list type
  • A dictionary can be converted to a list list type, only the keys in the dictionary are retained
• tuple() tuple
  • Same as the cast rules for lists
• set() collection
  • The numeric type is not a container type and cannot be converted to a collection
  • Strings, lists, tuples can be converted to sets and the result is unordered
  • When a dictionary is converted to a set, only the key of the dictionary is retained
• dict() dictionary
  • The numeric type is not a container type and cannot be converted to a dictionary
  • Strings cannot be directly converted to dictionaries
  • The list can be converted to a dictionary, the requirement is a second-level list, and each second-level element can only have two values
  • Tuples can be converted to dictionaries, the requirement is a second-level tuple, and each second-level element can only have two values

    str_dict =  '{"ywh":21}' 
    print ( eval ( str_dict ) )  # string to dictionary
    
    list_dict =  [ [ "123" , 2 ] , [ "ywh" , 21 ] ] 
    print ( dict ( list_dict ) ) #List to string
    
    #Convert with zip() 
    list_dict =  [ 'hello' , 'world' , 'haha' , 31 , 32 , 33 ] 
    print ( dict ( zip ( list_dict [ 0 : : 2 ] , list_dict [ 1 : : 2 ] ) ) )
    
    list1 =  [ 'ywh' , 'fish' , 'SF' ] 
    list2 =  [ 1 , 2 , 3 ] 
    print ( dict ( zip ( list1 , list2 ) ) )
    

    • 1
    • 2
    • 3
    • 4
    • 5
    • 6
    • 7
    • 8
    • 9
    • 10
    • 11
    • 12
    • 13

    {'ywh': 21}
    {'123': 2, 'ywh': 21}
    {'hello': 'world', 'haha': 31, 32: 33}
    {'ywh': 1, 'fish': 2, 'SF': 3}
    

    • 1
    • 2
    • 3
    • 4