from marshmallow import pre_dump


class SkipEmptyDataMixin:
    """Schema mixin which allows to skip empty values in output dumped data."""

    _EMPTY_VALUE = None

    def __init__(self, skip_empty=True, *args, **kwargs):
        self._skip_empty = skip_empty
        super().__init__(*args, **kwargs)

    @pre_dump
    def skip_empty_value(self, data, *args, **kwargs):
        if not self._skip_empty:
            return data
        return {key: value for key, value in data.items() if value != self._EMPTY_VALUE}