'Takes a string and tries to parse it as a variable definition. Returns
the key and value if successful, or raises an error.'

def _parse_variable_definition(self, line):

    if ('=' in line):
        (k, v) = [e.strip() for e in line.split('=', 1)]
        return (k, self._parse_value(v))
    self._raise_error(('Expected    key=value,    got:    %s' % line))
