class ConfigParserError(Exception):

    pass

class ConfigParser:

    def __init__(self):

        self.options = {}

        self.values = {}

    def add_option(self, name, type=str, default=None):

        """Register option name, type and default value."""

        self.options[name] = {'type':type, 'default':default}

        self.values[name] = default

        """Read config file and check loaded values."""

        self.read(fname)

        self.check()

    def read(self, fname):

        """Read config file. Does not check values."""

        with open(fname) as f:

            exec(f.read(), self.values)

    def check(self):

        """Check option values against registered types."""

        for key in self.values.keys():

            if key == '__builtins__':

                continue

            if key in self.options:

                type_ = self.options[key]['type']

                if not isinstance(self.values[key], type_) and not self.values[key] is None:

                    raise ConfigParserError("Bad value of config parameter '%s': type is %s but should be %s"

                        % (key, type(self.values[key]), type_))

            else:

                raise ConfigParserError("Unknown config parameter '%s'." % key)

    def __getattr__(self, name):

        """Attribute access for config parameters.

        cfg.my_param <===> cfg.values['myparam']

        """

        if name in self.values:

            return self.values[name]

        else:

            raise AttributeError()