Create a two way dict to be useful for symmetric mapping

TwoWayDict.py

class SymmetricMapping(dict):
    """
    Construct a bidirectional mapping when a list of tuple is passed.
    The mapping is usable as a two way dictionaty which has the same length\
    as the original one.
    
    Example usage:
    obj = SymmetricMapping([[(1, "Male"), (2, "Female"), (3, "Non-binary")]])
    >>> obj
    {
        1: 'Male',
        'Male': 1,
        2: 'Female',
        'Female': 2,
        3: 'Non-binary',
        'Non-binary': 3
    }
    
    >>> len(obj)
    3
    """
    
    def __init__(self, list_of_tuples):
      """Create the dict for items passed"""
        super(SymmetricMapping, self).__init__()
        for (key, value) in list_of_tuples:
            self.__setitem__(key, value)
        
    
    def __setitem__(self, key, value):
        """Set items for symmmetric mapping"""
        # Remove any previous connections with these values
        if key in self:
            del self[key]
        if value in self:
            del self[value]

        dict.__setitem__(self, key, value)
        dict.__setitem__(self, value, key)
            
    def __delitem__(self, key):
      """Delete connections from both mappings"""
        dict.__delitem__(self, self[key])
        dict.__delitem__(self, key)

    def __len__(self):
        """Returns the number of connections"""
        return dict.__len__(self) // 2