String Conversion in Python: When to Use __repr__ vs __str__

Published: 07 February 2017
on channel: Real Python
81,188
1.9k

https://dbader.org/python-tricks ► String conversion in Python classes and other advanced OOP techniques

When you define a custom class in Python and then try to print one of its instances to the console (or inspect it in an interpreter session) you get a relatively unsatisfying result. The default "to string" conversion behavior is basic and lacking in detail.

By default all you get is a string containing the class name and the `id` of the object instance (which is the object's memory address in CPython). That's better than *nothing*, but it's also not very useful.

The solution here is adding the `__str__` and `__repr__` "dunder" methods (some call them "magic methods") to your class.

They are the Pythonic way to control how objects are converted to strings in different situations.

In this tutorial video I'll do a deep dive on how Python's to-string conversion works and how you can add it to your own custom classes.

I'll walk you through the _str_ and _repr_ methods, when to use each, and some tips on how to use them in real world scenarios.

Just remember:

The result of `__str__` should be readable.

The result of `__repr__` should be unambiguous.

Always add a `__repr__` to your classes. The default implementation for `__str__` just calls `__repr__`, so you get the best of both worlds.

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