config.py

import configparser

_CFGFILE = 'config.cfg'

_DEFAULTS = {
             'main': {
                      'snapshot_seek': '-1',
                      'converter': '',
                      'output_format': 'webm',
                      'snapshot_format': '',
                      },
             'advanced': {
                          'converter_args': ('-c:v libvpx -b:v 2M -crf 10'
                                             ' -qmin 10 -qmax 42 -cpu-used 5'
                                             ' -v error'),
                          'converter_args_snap': '-frames:v 1 -v error',
                          'ffmpeg_args': '-vcodec copy -v error',
                          'ffmpeg_args_snap': '-vframes 1 -v error',
                          'snapshot_pos': 0.5,
                          'db_file': 'index.db',
                          'h_index_file': 'index00.bin',
                          },
             }

_MANDATORY = {
              'main': ('data_dir', 'output_dir'),
              }


class Config(configparser.ConfigParser):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def configure(self, cfgfile=_CFGFILE):
        self._load_defaults()
        self._read_file(cfgfile)
        self.validate()

    def save(self, cfgfile=_CFGFILE):
        self._write_file(cfgfile)

    def _load_defaults(self):
        self.read_dict(_DEFAULTS)

    def _read_file(self, cfgfile):
        self.read(cfgfile)

    def _write_file(self, cfgfile):
        with open(cfgfile, 'w') as f:
            self.write(f)

    def validate(self):
        for sec, keys in _MANDATORY.items():
            if sec not in self:
                raise ConfigError(
                    'Section [{}] must be present in config file'
                    .format(sec)
                )
            for k in keys:
                if k not in self[sec]:
                    raise ConfigError(
                        'Parameter `{}` must be present in section [{}]'
                        .format(k, sec)
                    )

        if self.getboolean('main', 'analyze_motion'):
            try:
                import cv2  # noqa
                import numpy  # noqa
            except ImportError:
                raise Exception('analyze_motion requires OpenVC and numpy')


class ConfigError(Exception):

    def __init__(self, msg):
        self.msg = msg

    def __str__(self):
        return self.msg


config = Config()