The difference between str() and _str_, repr() and _repr_:

str() and repr() are built-in functions in python and are functions directly used to format strings.

_ str_ and repr_ are strings of the class (object) itself in the class (object).

str

 1 >>>help(str)
 2 Help on class str in module builtins:
 3 
 4 class str(object)
 5  |  str(object='') -> str
 6  |  str(bytes_or_buffer[, encoding[, errors]]) -> str
 7  |
 8  |  Create a new string object from the given object. If encoding or
 9  |  errors is specified, then the object must expose a data buffer
10  |  that will be decoded using the given encoding and error handler.
11  |  Otherwise, returns the result of object.__str__() (if defined)
12  |  or repr(object).
13  |  encoding defaults to sys.getdefaultencoding().
14  |  errors defaults to 'strict'.

Create a new string object from a given object.

If an encoding or error is specified, the object must expose a data buffer that will be decoded using the given encoding and error handler.

Otherwise, the result of the object is returned.

_ str_() (if defined) or represents (object). The default getdefaultencoding() encoding system. The default error is "strict".

repr

1  >>>help(repr)
2 
3  Help on built-in function repr in module builtins:
4  
5  repr(obj, /)
6      Return the canonical string representation of the object.
7  
8      For many object types, including most builtins, eval(repr(obj)) == obj.

First, try to generate such a string and pass it to eval() to regenerate the same object.

Otherwise, a string enclosed in angle brackets is generated, containing the type name and additional information (such as address)

 eval 

 1 >>>help(eval)
 2 
 3 Help on built-in function eval in module builtins:
 4 
 5 eval(source, globals=None, locals=None, /)
 6     Evaluate the given source in the context of globals and locals.
 7 
 8     The source may be a string representing a Python expression
 9     or a code object as returned by compile().
10     The globals must be a dictionary and locals can be any mapping,
11     defaulting to the current globals and locals.
12     If only globals is given, locals defaults to it.

The code is as follows:

 1 >>> eval('1+2')
 2 3
 3 >>> str('1+2')
 4 '1+2'
 5 >>> repr('1+2')
 6 "'1+2'"
 7 >>> type(repr('1+2'))
 8 <class 'str'>
 9 >>> type(str('1+2'))
10 <class 'str'>
11 >>> type(eval('1+2'))
12 <class 'int'>
13 #That's equivalent to what I said above. eval(repr(object)) == object
14 >>> eval(repr('1+2'))     
15 '1+2'
16 >>> '1+2'
17 '1+2' 

Example:

Python defines two methods _str_() and _repr_(), _str_() for display to users and _repr_() for display to developers.

 1 class Person(object):
 2     def __init__(self, name, sex):
 3         self.name = name
 4         self.sex = sex
 5     def __str__(self):
 6         return '(Person: %s, %s)' % (self.name, self.sex)
 7 
 8 class Student(Person):
 9     def __init__(self, name, sex, score):
10         Person.__init__(self, name, sex)
11         self.score = score
12     def __str__(self):
13         return '(Student: %s, %s, %s)' % (self.name, self.sex, self.score)
14     def __repr__(self):
15         return '(Student: %s, %s, %s)' % (self.name, self.sex, self.score)

 1 >>> from demo import Person, Student
 2 >>> p = Person('Alice', 'Female')
 3 >>> p
 4 <demo.Person object at 0x103eac0b8>
 5 >>> print (p)
 6 (Person: Alice, Female)
 7 >>> s = Student('Tom', 'male', 20)
 8 >>> s
 9 (Student: Tom, male, 20)
10 >>> print (s)
11 (Student: Tom, male, 20)