How can I customize the output of printing a class instance in Python?

Customizing Class Instance Representation When Printing

When attempting to print an instance of a class, you may encounter a default representation such as the memory address. To customize the printed appearance of your class instances, delve into the concepts of __str__ and __repr__.

The __str__ Method

By defining a __str__ method within your class, you can control how instances are represented when printed. This method should return a string containing the desired display text. For example:

>>> class Test:
>>>     def __init__(self):
>>>         self.a = 'foo'
>>>     def __str__(self):
>>>         return f"Test with a: {self.a}"

Now, when printing an instance of this class, you'll get a custom string representation:

>>> t = Test()
>>> t
Test with a: foo
>>> print(t)
Test with a: foo

The __repr__ Method

The __repr__ method, when defined, takes precedence over __str__ when printing using the repr() function or in interactive prompts. It aims to provide a more detailed representation, suitable for debugging or reconstruction. If you define __repr__ without __str__, it will also serve as the printed representation.

For instance:

>>> class Test:
>>>     def __init__(self):
>>>         self.a = 'foo'
>>>     def __repr__(self):
>>>         return f"Test(a={self.a})"

When printing:

>>> t = Test()
>>> t
Test(a='foo')
>>> repr(t)
"Test(a='foo')"

Summary:

To customize the printed representation of your class instances, define a __str__ method for the desired display text or a __repr__ method for a detailed representation. If both are defined, __str__ is used for printing while __repr__ is used for the repr() function.

The above is the detailed content of How can I customize the output of printing a class instance in Python?. For more information, please follow other related articles on the PHP Chinese website!