python倒序读取文件tail方式

网上找的都不太好

自己写了个 模仿tail

更新了下代码, 发现windows和unix文本区别还是会导致点坑的

def get_last_line(file_path, max_line_number, buffer_size=4096):
    # 从末尾读取文件并返回以行组成的列表
    """
    :param file_path: 文件路径
    :param max_line_number: 返回行数
    :param buffer_size: 读缓冲区大小
    :return: :raise ParameterIllegal:   自定义错误
    """
    if not isinstance(max_line_number, (int, long)):
        raise ParameterIllegal('max line number not int')
    if not isinstance(file_path, str):
        raise ParameterIllegal('file_path value error')
    if not isinstance(buffer_size, (int, long)):
        raise ParameterIllegal('buffer_size not int')
    if not os.path.exists(file_path):
        raise ParameterIllegal('file_path not exists')
    if buffer_size > 20000:
        raise ParameterIllegal('buffer_size large then 20000')
    # 限制最大读取行数
    if max_line_number > 100:
        max_line_number = 100
    out_put_line_list = []
    try:
        # 非unix文件使用r方式打开读取长度会减少,直接以rb方式打开
        f = open(file_path, 'rb', buffering=buffer_size)
    except OSError:
        raise ParameterIllegal('open file get os error')
    except IOError:
        raise ParameterIllegal('open file get io error')
    # 文件大小
    file_size = os.path.getsize(file_path)
    if file_size == 0:
        try:
            f.close()
            msg = 'closed file'
        except OSError:
            msg = 'close file os error'
        except IOError:
            msg = 'close file io error'
        raise ParameterIllegal('file size is 0 %s' % msg)
    # 当前位置,即开始读取的位置
    if file_size < buffer_size:
        start_read_pos = 0
        buffer_size = file_size
    else:
        start_read_pos = file_size - 1 - buffer_size
    # 实际读取的buffer大小
    read_buffer_size = buffer_size
    # 实际读取到的行数
    read_line_num = 0
    # 未满行的字符串
    line_buffer = ''
    # 全部读取大小
    size_read = 0
    while read_line_num < max_line_number:
        # 已经是文件的最开始部位,设置退出
        # 防止读取过多内容,限制为1M
        size_read += read_buffer_size
        if size_read >= 1048576:
            try:
                f.close()
                msg = 'closed file'
            except OSError:
                msg = 'close file os error'
            except IOError:
                msg = 'close file io error'
            try:
                f.close()
            except OSError:
                raise ParameterIllegal('close file get os error')
            except IOError:
                raise ParameterIllegal('close file get io error')
            raise ParameterIllegal('read file get string to much long %d, %s' % (size_read, msg))
        # seek到读取位置
        f.seek(start_read_pos)
        # 读取文件
        try:
            string_buffer = f.read(read_buffer_size)
        except OSError:
            try:
                f.close()
                msg = 'closed file'
            except OSError:
                msg = 'close file os error'
            except IOError:
                msg = 'close file io error'
            raise ParameterIllegal('read file get os error and %s' % msg)
        except IOError:
            try:
                f.close()
                msg = 'closed file'
            except OSError:
                msg = 'close file os error'
            except IOError:
                msg = 'close file io error'
            raise ParameterIllegal('read file get io error and %s' % msg)
        # 换行位置,默认为string_buffer的结尾
        new_line_pos = read_buffer_size
        # xrange倒序
        for i in xrange(read_buffer_size - 1, -1, -1):
            if string_buffer[i] == '\n':
                 # 切片添加
                if len(line_buffer) > 0:
                    out_put_line_list.insert(0, string_buffer[i + 1: new_line_pos] + line_buffer)
                    line_buffer = ''
                else:
                    if len(string_buffer[i + 1: new_line_pos]) > 0:
                        out_put_line_list.insert(0, string_buffer[i + 1: new_line_pos])
                read_line_num += 1
                new_line_pos = i
                if read_line_num >= max_line_number:
                    break
            # 已经到当前string buff的第一个字符串
            if i == 0:
                if new_line_pos > 0:
                    line_buffer = string_buffer[0: new_line_pos] + line_buffer
                    out_put_line_list.insert(0, line_buffer)
        # 剩余文件长度大于buffer
        if start_read_pos > buffer_size - 1: # 重新定位开始读取的位置
            start_read_pos = start_read_pos - buffer_size
        # 剩余文件长度小于buffer
        else:
            read_buffer_size = buffer_size - start_read_pos # 减少实际读取的buffer
            start_read_pos = 0  # 读取位置定义到文件头
            if read_line_num < max_line_number:
                read_line_num = max_line_number - 1
            if file_size < buffer_size:
                read_line_num = max_line_number
    try:
        f.close()
    except OSError:
        raise ParameterIllegal('close file get os error')
    except IOError:
        raise ParameterIllegal('close file get io error')
    return out_put_line_list