>>> _parse_op('>')
    'gt'
    >>> _parse_op('>=')
    'ge'
    >>> _parse_op('=>')
    'ge'
    >>> _parse_op('=> ')
    'ge'
    >>> _parse_op('<')
    'lt'
    >>> _parse_op('<=')
    'le'
    >>> _parse_op('==')
    'eq'
    >>> _parse_op(' <= ')
    'le'

def _parse_op(op):
    '''
    >>> _parse_op('>')
    'gt'
    >>> _parse_op('>=')
    'ge'
    >>> _parse_op('=>')
    'ge'
    >>> _parse_op('=> ')
    'ge'
    >>> _parse_op('<')
    'lt'
    >>> _parse_op('<=')
    'le'
    >>> _parse_op('==')
    'eq'
    >>> _parse_op(' <= ')
    'le'
    '''
    op = op.strip()
    if '>' in op:
        if '=' in op:
            return 'ge'
        else:
            return 'gt'
    elif '<' in op:
        if '=' in op:
            return 'le'
        else:
            return 'lt'
    elif '!' in op:
        return 'ne'
    else:
        return 'eq'