@classmethod
def from_exactlines(cls, transformed_lines):
    """Constructs a partially-computed LinesClassifier from ExactLines.

        This is useful, for example, if you need ExactLines for some other
        analysis and then want to determine classification regions. We use it
        to determine the class break-point when generating Figure 4 from [1]
        (experiments/linearity_hypothesis.py).
        """
    if not len(transformed_lines[0]) == 2:
        error = ('ExactLine must be called with include_post=True ' +
            'to use from_exactline.')
        if len(transformed_lines) == 2:
            error += ('\nIf you called exactline (singular), you must ' +
                'pass a singleton list instead.')
        raise TypeError(error)
    self = cls(None, None, None)
    self.transformed_lines = transformed_lines
    self.partially_computed = True
    return self
