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pythonmagic-methods

How and where to use Python's __and__, __or__, __invert__ magic methods properly

I was googling around to find any use cases or examples of these methods but could not find any detailed explanation, they are just listed along other similar methods. Actually, I was looking through some code on github and came across these methods but could not understand the usage. Can somebody please provide a detailed explanation of these methods. This is the link of github code where I came across them: https://github.com/msiemens/tinydb/blob/master/tinydb/queries.py

Solution

  • The magic methods __and__, __or__ and __invert__ are used to override the operators a & b, a | b and ~a respectively. That is, if we have a class

    class QueryImpl(object):
    def __and__(self, other):
        return ...

    then 

    a = QueryImpl(...)
b = QueryImpl(...)
c = a & b

    is equivalent to 

    a = QueryImpl(...)
b = QueryImpl(...)
c = a.__and__(b)

    These methods are overridden in tinydb to support this syntax:

    >>> db.find(where('field1').exists() & where('field2') == 5)
>>> db.find(where('field1').exists() | where('field2') == 5)
#                                    ^

    See also: