Reads one section from the mesh3d file.

        integer ... if True, all numbers are passed to int(), otherwise to
            float(), before returning

        Some examples how a section can look like:

        2
        1 2 5 4 7 8 11 10
        2 3 6 5 8 9 12 11

        or

        5
        1 2 3 4     1
        1 2 6 5     1
        2 3 7 6     1
        3 4 8 7     1
        4 1 5 8     1

        or

        0

def _read_section(self, f, integer=True):
        """
        Reads one section from the mesh3d file.

        integer ... if True, all numbers are passed to int(), otherwise to
            float(), before returning

        Some examples how a section can look like:

        2
        1 2 5 4 7 8 11 10
        2 3 6 5 8 9 12 11

        or

        5
        1 2 3 4     1
        1 2 6 5     1
        2 3 7 6     1
        3 4 8 7     1
        4 1 5 8     1

        or

        0

        """
        if integer:
            dtype=int
        else:
            dtype=float
        l = self._read_line(f)
        N = int(l)
        rows = []
        for i in range(N):
            l = self._read_line(f)
            row = nm.fromstring(l, sep=" ", dtype=dtype)
            rows.append(row)
        return nm.array(rows)