'In-place addition of a distribution or environment'

def __iadd__(self, other):

    if isinstance(other, Distribution):
        self.add(other)
    elif isinstance(other, Environment):
        for project in other:
            for dist in other[project]:
                self.add(dist)
    else:
        raise TypeError(("Can't    add    %r    to    environment" % (other,)))
    return self
