'Check if a header has already been included.
Args:
header: header to check.
Returns:
Line number of previous occurrence, or -1 if the header has not
been seen before.'

def FindHeader(self, header):

    for section_list in self.include_list:
        for f in section_list:
            if (f[0] == header):
                return f[1]
    return (-1)
