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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 _GetRelPath(self, filename):
 		"""Get relative path of a file according to the current directory, 		given its logical path in the repo."""

		assert filename.startswith(self.subdir), (filename, self.subdir)
		return filename[len(self.subdir):].lstrip(r"\/")