@staticmethod

	def _filter_redundant_regexes(rs):

		"""

		Given a list of regular expressions to be joined via "|".join(),

		removes those branches that have non-unique suffixes: 

			['a$', 'ba$'] --> ['a$']

		for the purpose of improving efficiency.  

		This is used in _prepare_search_regex to make filename matching

		more efficient.

		@type rs: list

		@param rs: file path regular expressions each ending with '$'

		@rtype: list

		@return: list with possibly fewer branches

		@raise ValueError: if a regular expression does not end with '$'

		"""

		# sort in place

		rs.sort(key= len, reverse= True)

		rs_filtered = []

		# keep a list item only if no suffix of it is present

		for i in range(len(rs)):

			found = False

			for j in range(i + 1, len(rs)):

				if rs[i].endswith(rs[j]):

					found = True

					break

			if not found:

				if not rs[i].endswith('$'):

					raise ValueError(

						"_filter_redundant_regexes needs all regexes to end with '$'")

				rs_filtered.append(rs[i])

		# we assume a search with very few hits; sort order is unimportant

		return rs_filtered