environs.py 文件源码

def _field2method(field_or_factory, method_name, preprocess=None):
    def method(self, name, default=ma.missing, subcast=None, **kwargs):
        name = self._prefix + name if self._prefix else name
        missing = kwargs.pop('missing', None) or default
        if isinstance(field_or_factory, type) and issubclass(field_or_factory, ma.fields.Field):
            field = field_or_factory(missing=missing, **kwargs)
        else:
            field = field_or_factory(subcast=subcast, missing=missing, **kwargs)
        self._fields[name] = field
        parsed_key, raw_value = _get_from_environ(name, ma.missing)
        if raw_value is ma.missing and field.missing is ma.missing:
            raise EnvError('Environment variable "{}" not set'.format(parsed_key))
        value = raw_value or field.missing
        if preprocess:
            value = preprocess(value, subcast=subcast, **kwargs)
        try:
            value = field.deserialize(value)
        except ma.ValidationError as err:
            raise EnvError('Environment variable "{}" invalid: {}'.format(name, err.args[0]))
        else:
            self._values[name] = value
            return value
    method.__name__ = str(method_name)  # cast to str for Py2 compat
    return method