Remove value from self.

		Args:
			value: Element to remove from self
		Raises:
			ValueError: if element is already present

def remove(self, value):
		"""Remove value from self.

		Args:
			value: Element to remove from self
		Raises:
			ValueError: if element is already present
		"""
		try:
			index = self._dict[value]
		except KeyError:
			raise ValueError('Value "%s" is not present.')
		else:
			del self[index]