What is the difference between __str__ and __repr__?

The object class in Python offers a variety of magic methods. Magic methods start and end with double underscores—we never explicitly invoke these methods. The appropriate built-in function makes an internal call to one of these magic methods.

In this Answer, we will only discuss str() and repr() functions which both call the magic methods __str__() and __repr__() respectively.

  • str(): The object's string representation is returned by the str() method. Its syntax is as follows, str(object, encoding=encoding, errors=errors) .

z = str(3.5)
print(z)

  • repr() : The repr() function returns a printed representation of an object. Its syntax is as follows, repr(object) .

print(repr(['x', 'y', 'z']))

Let's see how the two functions are related. We'll check it out using integers and strings.

#we will create two variables and assign a variable to them
#we will print them out using the __str__() and __repr__() respectively
x = 5
print(str(x))
print(x.__str__())
y = 7
print(repr(y))
print(y.__repr__())

  • Line 3: We declare a variable x and assigned a value of 5 to it.

  • Line 4: We print x using the str() method.

  • Line 5: We print x by adding the .__str__() method to it.

  • Line 7: We declare the variable y with 7 assigned to it.

  • Line 8: We print the variable y using the repr() method.

  • Line 9: We print y by assing the .__repr__() method to it.

#lets create a variable x with a string value and print using the str() funtion
x = 'Programming is fun!'
print (str(x))
#lets create a variable y with a string value and print using the repr() funtion
y = 'Learn how to code on Educative'
print (repr(y))

  • Line 2: We assign a string value to x.

  • Line 3: We print x using the str() method.

  • Line 6: Let's create a variable y with a string value.

  • Line 7: We print y using the repr() method.

We observe that both functions represent a string, so let us look at them individually.

The __str__() method

Classes can utilize the __str__() method to express class objects as strings. The __str__() method definition ought to be written so that it outputs all of the class members and is simple to understand. When inspecting the members of a class, this technique is also employed as a debugging tool.

When the print() or str() functions are used on an object and return a string, the __str__() method is triggered.

Syntax

object.__str__(self)

Example

Let's create a class, Tutorial, and define the __str__() method. We'll then call this method using the built-in Python function, str().

#create class Tutorial
class Tutorial:
    #lets pass two arguments into the __init__ function
    def __init__(self, x, y):
        self.x = x
        self.y = y
    #using the __str__() method we return the values passed into the x and y arguments.
    def __str__(self):
        result = self.x + ' ' + str(self.y)
        return result
tuts = Tutorial("Boys", "Scout")
print(str(tuts))

  • Line 2: We create a class called Tutorial.

  • Line 4: The __init__() function in the class receives x and y as arguments, and to access class-specific variables. We use the self argument, which is a reference to the currently running instance of the class.

  • Line 8: we also created the __str__() function with the self argument, and from this, we can access the values of x and y. We then return the concatenation of x and y with a space in between.

  • Line 12: The class Tutorial is instantiated, with the values "Boys" and "Scout" passed to it.

  • Line 13: We print the instance of the call using the str() method.

The __repr__() method

The object representation is returned as a string by the Python method, __repr__(). This method is called when the object's repr() method is used. If feasible, the text returned should be a legitimate Python expression that may be used to recreate the object.

Using the __repr__() method, we can create a custom string representation of our class objects.

Syntax

object.__repr__(self)

Example

We will create a class, Tutorial, and define the __repr__() method. We can then call this method using the built-in Python function, repr().

#We will create the class Tutorial
class Tutorial:
    #the init function will receive two argument - name and sex.
    def __init__(self, name, sex):
        self.name = name
        self.sex = sex
    def __repr__(self):
        result = self.name + ' is a  ' + str(self.sex)
        return result
# Let's make a Person object and print the results of repr()
tuts = Tutorial("Michael Jackson", "Male")
print(repr(tuts))

  • Line 2: We create a class, Tutorial.

  • Line 4: The __init__() function in the class receives "name" and "sex" as arguments.

  • Line 8: We create the __repr__() function with the self argument, and from this, we can access the values of "name" and "sex". We then return the concatenation of both arguments with a space in between.

  • Line 15: The class Tutorial is instantiated, and the values "Michael Jackson" and "Male" are passed to it.

  • Line 16: We print the instance of the call using the repr() method.

Difference between __str__() and __repr__()

  • The __str__() method is intended to return information in a readable format for humans to easily understand it. It is perfect for logging or displaying object information. While the __repr__() method's goal is to deliver a string representation of the object that may be used to replicate it, it is also designed to do the opposite.

  • A unique string representation of our class objects may be made using the __repr__() method.

  • The goal of __repr__() is to be unambiguous, while the goal of __str__() is to be readable.

  • __str__() of a container utilizes the __repr__() of contained objects.

Let's look at a common class where the __str__() and __repr__ () methods are defined.

#lets import the datetime module
import datetime
#lets get the current date and time
now = datetime.datetime.now()
print('Using str: ' + now.__str__())
print('Using repr: ' + now.__repr__())

  • Line 2: We import the datetime module.

  • Line 5: Using the datetime.datetime.now(), we get the current date and time. Note that it is the current date and time on our local computer.

  • Line 6: We print the date using the __str__() method.

  • Line 7: We print the date using the __repr__() method. There is a difference in the output.

We'll utilize __repr__() to implement whatever class we choose. It should come naturally to do this. We implement __str__() if it would be advantageous to have a string version that errs on the side of readability. Backup behavior is supplied by __repr__() in the absence of __str__().

Conclusion

The __str__() and __repr__() methods return the object's string representation. The __repr__() representation is intended to hold information about the object so that it may be created again. In contrast, the __str__() string representation is human-friendly and mainly used for logging reasons. Always utilize the str() and repr() functions instead of using these methods directly.

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