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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 _check_L(self, L):
 """Run some basic checks on L."""

        # TODO: Take this out?
        if issparse(L):
            L = L.todense()

        # Check for correct values, e.g. warning if in {-1,0,1}
        if np.any(L < 0):
            raise ValueError("L must have values in {0,1,...,k}.")