A class with the attributes that are prevented from being overwritten

read_only_class.py

class ReadOnlyAttr:
    """ A class with the attributes that are defined on the instance
    creation and cannot be modified later. """

    # A tuple of attributes that should remain read-only
    READ_ONLY_ATTR = ('x', 'y')

    def __init__(self, *args, **kwargs):
        """ Takes a list of read-only attributes: %s """
        for attr in self.READ_ONLY_ATTR:
            setattr(self, attr,
                    kwargs.get(attr, ''))

    # List READ_ONLY_PARAMETERS in the docstring of the class.
    __init__.__doc__ %= ", ".join(READ_ONLY_ATTR)

    def __setattr__(self, name, value):
        """ Prevent the READ_ONLY_ATTR from being overwritten. """
        if name in self.__dict__ and name in self.READ_ONLY_ATTR:
            raise AttributeError("The attribute '%s' cannot be overwritten"
                                 % name)
        else:
            self.__dict__[name] = value


# Examples:

# Create an instance
roa = ReadOnlyAttr(x="Some value", y=234)

# Print the value:
print roa.x

# The following will raise an exception:
roa.x = "New value"