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Learn how the behavior of `dunder methods` can be overridden in Python and the limitations involved with built-in types.
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Can I Modify the Behavior of Built-in Types in Python?

Python, being a dynamic and flexible language, often leads to questions regarding the extent of its capabilities. A common query among developers, especially those new to Python, is whether the behavior of built-in types can be modified. For instance, can you change how the addition operator works on strings by overriding the _add_ method of the str class? In this guide, we’ll explore this fascinating subject and understand the limitations involved in overriding built-in methods in Python.

The Concept of Dunder Methods

Dunder methods, short for "double underscore" methods, are special methods in Python that allow you to define how operators behave for user-defined objects. Examples include:

_init_ for object initialization

_add_ for addition

_str_ for string representation

These methods enable developers to customize the behavior of objects in a meaningful way.

Monkey-Patching in Python

Monkey-patching is essentially editing or modifying a class or module at runtime. This technique can be used to change the behavior of existing classes, including methods. For example, you might want to override the _add_ method of a custom class to change how two instances of that class are added together.

However, there Are Limitations

When it comes to built-in types or classes that are implemented in C, such as str and collections.defaultdict, you cannot modify their behavior. Let’s look at some examples:

Example 1: Attempting to Override _add_ for str

[[See Video to Reveal this Text or Code Snippet]]

When you run this code, you will encounter the following error:

[[See Video to Reveal this Text or Code Snippet]]

This error indicates that Python protects built-in types from accidental overrides, meaning that critical parts of the language remain intact.

Example 2: Overriding _add_ for defaultdict

The same rules apply when dealing with other built-in collections like defaultdict.

[[See Video to Reveal this Text or Code Snippet]]

Attempting to execute this snippet results in:

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The Exceptions: Custom and Non-Built-in Types

Despite these restrictions, you can still override methods in custom classes or classes that are not implemented in C. Here’s an example to illustrate this point:

Example 3: Overriding _add_ in Random Class

[[See Video to Reveal this Text or Code Snippet]]

In this case, we successfully modified the behavior because Random is not a built-in type in the same sense as str.

Third-party Libraries: The Same Rule Applies

It's also worth noting that third-party libraries often implement built-in types in C. For instance, the numpy library constructs its arrays using C for performance reasons. Trying to override the addition method for NumPy's ndarray results in the same TypeError as before:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

In summary, Python offers a powerful and flexible programming model, allowing for modifications through monkey-patching. However, while you can often override methods on user-defined classes or certain classes not implemented in C, built-in types like str, list, and third-party libraries such as numpy are protected from accidental manipulation. This design safeguards the integrity of fundamental components of the language.

Understanding these constraints is crucial for any Python developer, ensuring you work within the boundaries set by the language while still enjoying its rich feature set.

Happy coding!