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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def from_T050017(cls, url, coltype = LIGOTimeGPS):
 		""" 		Parse a URL in the style of T050017-00 into a CacheEntry. 		The T050017-00 file name format is, essentially, 		observatory-description-start-duration.extension 		Example: 		'L' 		'localhost' 		'L-L1_RDS_C03_L2-836562330-83.gwf' 		"""

		match = cls._url_regex.search(url)
		if not match:
			raise ValueError("could not convert %s to CacheEntry" % repr(url))
		observatory = match.group("obs")
		description = match.group("dsc")
		start = match.group("strt")
		duration = match.group("dur")
		if start == "-" and duration == "-":
			# no segment information
			segment = None
		else:
			segment = segments.segment(coltype(start), coltype(start) + coltype(duration))
		return cls(observatory, description, segment, url)