Question

I need to do a set difference in python tuples, but the difference need to consider the first element of my tuple.

To achieve this I did (uncessfully) using this class approach

class Filedata(object):
    def __init__(self, filename, path):
        self.filename = filename
        self.path = path + '\\' + filename
    def __eq__(self, other):
        return self.filename==other.filename
    def __ne__(self, other):
        return self.filename!=other.filename
    def __call__(self):
        return self.filename
    def __repr__(self):
        return self.filename     

Digging in the sets.py module I found that the library uses the itertools.ifilterfalse function to make the difference

def difference(self, other):
    """Return the difference of two sets as a new Set.

    (I.e. all elements that are in this set and not in the other.)
    """
    result = self.__class__()
    data = result._data
    try:
        otherdata = other._data
    except AttributeError:
        otherdata = Set(other)._data
    value = True
    for elt in ifilterfalse(otherdata.__contains__, self):
        data[elt] = value
    return result

But I wasn’t able to do anything useful with this.

Answer 1

The only way to do this is to define your own sequence class that only uses the first element in __eq__() and __hash__().