Posts tagged snippets

Use magic methods __setitem__() and __getitem__() in Python

In Python, there are two magic methods that can be used to implement the behavior of the subscript operator []. These methods are object.__setitem__() and object.__getitem__(). The first one is used to assign a value to an item, the second one is used to retrieve an item.

The following example shows how to use these methods to implement a memory class as a list of bytes that was used in the 6502 emulator. The memory class has two methods get() and set() that are used to retrieve and assign a value to a memory address.

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Chaining methods in Python

Method chaining is a programming style in which multiple method calls are made on the same object, in sequence. Each method call returns the object itself, so the next method can be called on it without having to assign the object to a variable in between.

This can make code more concise and readable, as it can be written as a single line of code instead of multiple lines. It can also make code more efficient, as the object does not have to be passed around between methods.

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Use removeprefix instead of lstrip to remove a prefix from a string

Python 3.9 introduced new methods called bytearray.removeprefix() and bytearray.removesuffix() via PEP 616 to remove a prefix or suffix from a string. These methods are similar to str.lstrip() and str.rstrip() but they are more efficient and easier to use as they use a string instead of a set of characters. The latter is useful when you want to remove a prefix or suffix from a string that is not a set of characters.

Lets see an example where we want to remove the prefix www. from a list of URLs as shown below:

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