def windows(self, window_size=60, context_len=90, step=10):
        '''Walk through the sequence of interest in windows of window_size,
        evaluate free (unbound) pair probabilities.

        :param window_size: Window size in base pairs.
        :type window_size: int
        :param context_len: The number of bases of context to use when
                            analyzing each window.
        :type context_len: int
        :param step: The number of base pairs to move for each new window.
        :type step: int

        '''
        self.walked = _context_walk(self.template, window_size, context_len,
                                    step)
        self.core_starts, self.core_ends, self.scores = zip(*self.walked)
        return self.walked
Walk through the sequence of interest in windows of window_size,
        evaluate free (unbound) pair probabilities.

        :param window_size: Window size in base pairs.
        :type window_size: int
        :param context_len: The number of bases of context to use when
                            analyzing each window.
        :type context_len: int
        :param step: The number of base pairs to move for each new window.
        :type step: int