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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 _PathList_key(self, pathlist):
 """ Returns the key for memoization of PathLists. Note that we want this to be pretty quick, so we don't completely canonicalize all forms of the same list. For example, 'dir1:$ROOT/dir2' and ['$ROOT/dir1', 'dir'] may logically represent the same list if you're executing from $ROOT, but we're not going to bother splitting strings into path elements, or massaging strings into Nodes, to identify that equivalence. We just want to eliminate obvious redundancy from the normal case of re-using exactly the same cloned value for a path. """

        if SCons.Util.is_Sequence(pathlist):
            pathlist = tuple(SCons.Util.flatten(pathlist))
        return pathlist