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Learn Python 3 - Free Interactive Course

What is the __str__ method in Python?

Explore how to use the __str__ method in Python to create readable string representations of class objects. Understand the default behavior, how to define custom outputs, and the relationship with the __repr__ method. This lesson helps you write clearer, more user-friendly code and debug effectively by customizing object displays.

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The __str__ method represents a class's objects as a string. It should be defined so that the output is easy to read and includes the relevant members of the class, which also makes it useful as a debugging tool when you need to inspect an object's contents.

Python automatically calls __str__ when any of the following are used on an object:

  • print(obj)

  • str(obj)

  • obj.__str__()

If __str__ isn't defined on the class, Python falls back to __repr__ instead. By default, __repr__ returns a string describing the object's pointer (memory address), so without a custom __str__, printing your object will show something cryptic rather than a readable summary.

In the next sections, we'll look at two ways to use __str__: relying on the default behavior, and defining a custom version.

1. Default implementation

The following code explains the default implementation of the __str__ method.

Python 3.14.0
class MyClass:
    x = 0
    y = ""
    def __init__(self, anyNumber, anyString):
        self.x = anyNumber
        self.y = anyString
myObject = MyClass(12345, "Hello")
print(myObject.__str__())
print(myObject.__repr__())
print(myObject)

The above code shows an example where neither __str__ nor __repr__ are defined. Calling __str__ calls the default __repr__ method, and they all give the same output, the pointer of our object.

2. Custom __str__method

The following code explains how the custom __str__ method works.

Python 3.14.0
class MyClass:
    x = 0
    y = ""
    def __init__(self, anyNumber, anyString):
        self.x = anyNumber
        self.y = anyString
    def __str__ (self):
        return 'MyClass(x=' + str(self.x) + ' ,y=' + self.y + ')'
myObject = MyClass(12345, "Hello")
print(myObject.__str__())
print(myObject)
print(str(myObject))
print(myObject.__repr__())

The code above shows the output once you have defined the __str__ method. When __str__, print(), or str() are called you will get your defined output. Make note that the __repr__ output remains the same.

3. The __repr__method defined only

Let’s see the example of the __repr__ method defined only.

Python 3.14.0
class MyClass:
    x = 0
    y = ""
    def __init__(self, anyNumber, anyString):
        self.x = anyNumber
        self.y = anyString
    def __repr__ (self):
        return 'MyClass(x=' + str(self.x) + ' ,y=' + self.y + ')'
myObject = MyClass(12345, "Hello")
print(myObject.__str__())
print(myObject)
print(str(myObject))
print(myObject.__repr__())

In the first example we saw that when __str__ is not defined it automatically calls the __repr__ method. Therefore, the output of all the functions - __str__, str(), and __repr__ - are the same. Moreover, the __repr__ method does not necessarily need to return a string. In case it does not return a string, the print() statements will throw an error.