Some Magic Methods in Python

I previously used __enter__ and __exit__, which I had heard of before. This time, my program development is mainly object-oriented, so I needed to use more methods to achieve some useful features in Python. Here’s a small note.

__len__

After defining it, you can use the len() function on an instance.

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def __len__(self):
    '''
    Define length
    '''
    return len(self.Seq)

__getitem__

After defining it, you can perform indexing and slicing operations on an instance using [].

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def __getitem__(self, key):
    '''
    Add slice index
    '''
    return self.d[key]

__str__

After defining it, when you print an instance using print(), it will print the content returned by this method.

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def __str__(self):
    return str(self.__dict__)

__iter__

After defining it, you can iterate over an object, such as for i in object. Note that this method must return an iterator (not just an iterable).

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def __iter__(self):
    return (mut for mut in self.muts)

__eq__ and __hash__

These two are together because if you want to automatically remove duplicates when placing instances in a set(), both methods need to be defined. Otherwise, the purpose will not be achieved. The __eq__ method makes objects comparable (== and !=, is cannot be used). Note that the other parameter is fixed here; do not change it.

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def __eq__(self, other):
    '''
    Ensure automatic removal of duplicates using set characteristics
    '''
    return self.muts == other.muts

__hash__ then essentially makes objects hashable. The hash value used for hashing will be the one provided by this method.

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def __hash__(self):
    '''
    Ensure automatic removal of duplicates using set characteristics
    '''
    return hash(self.muts)

That’s it for now. I’ll continue to add more as needed.
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