What is the __str__ method in Python?
The __str__ method in Python represents the class objects as a string – it can be used for classes. The __str__ method should be defined in a way that is easy to read and outputs all the members of the class. This method is also used as a debugging tool when the members of a class need to be checked.
The __str__ method is called when the following functions are invoked on the object and return a string:
- The
print()method - The
str()method
If we have not defined the __str__, then it will call the __repr__ method. The __repr__ method returns a string that describes the pointer of the object by default (if the programmer does not define it).
How to call __str__ method
Let’s explore different ways to call the __str__ method.
1. Default implementation
The following code explains the default implementation of the __str__ method.
class MyClass:x = 0y = ""def __init__(self, anyNumber, anyString):self.x = anyNumberself.y = anyStringmyObject = 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.
class MyClass:x = 0y = ""def __init__(self, anyNumber, anyString):self.x = anyNumberself.y = anyStringdef __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.
class MyClass:x = 0y = ""def __init__(self, anyNumber, anyString):self.x = anyNumberself.y = anyStringdef __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.
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Shahpar Khan