def exit_counts(self):
        """Get a mapping from line numbers to count of exits from that line.

        Excluded lines are excluded.

        """
        excluded_lines = self.first_lines(self.excluded)
        exit_counts = {}
        for l1, l2 in self.arcs():
            if l1 < 0:
                # Don't ever report -1 as a line number
                continue
            if l1 in excluded_lines:
                # Don't report excluded lines as line numbers.
                continue
            if l2 in excluded_lines:
                # Arcs to excluded lines shouldn't count.
                continue
            if l1 not in exit_counts:
                exit_counts[l1] = 0
            exit_counts[l1] += 1

        # Class definitions have one extra exit, so remove one for each:
        for l in self.classdefs:
            # Ensure key is there: classdefs can include excluded lines.
            if l in exit_counts:
                exit_counts[l] -= 1

        return exit_counts
Get a mapping from line numbers to count of exits from that line.

        Excluded lines are excluded.