def concat(self, other, inplace=False):
        """Combine entityset with another to create a new entityset with the
        combined data of both entitysets.
        """
        if not self.__eq__(other):
            raise ValueError(
                "Entitysets must have the same dataframes, relationships"
                ", and column names",
            )

        if inplace:
            combined_es = self
        else:
            combined_es = copy.deepcopy(self)

        has_last_time_index = []
        for df in self.dataframes:
            self_df = df
            other_df = other[df.ww.name]
            combined_df = pd.concat([self_df, other_df])
            # If both DataFrames have made indexes, there will likely
            # be overlap in the index column, so we use the other values
            if self_df.ww.metadata.get("created_index") or other_df.ww.metadata.get(
                "created_index",
            ):
                columns = [
                    col
                    for col in combined_df.columns
                    if col != df.ww.index or col != df.ww.time_index
                ]
            else:
                columns = [df.ww.index]
            combined_df.drop_duplicates(columns, inplace=True)

            self_lti_col = df.ww.metadata.get("last_time_index")
            other_lti_col = other[df.ww.name].ww.metadata.get("last_time_index")
            if self_lti_col is not None or other_lti_col is not None:
                has_last_time_index.append(df.ww.name)

            combined_es.replace_dataframe(
                dataframe_name=df.ww.name,
                df=combined_df,
                recalculate_last_time_indexes=False,
                already_sorted=False,
            )

        if has_last_time_index:
            combined_es.add_last_time_indexes(updated_dataframes=has_last_time_index)

        combined_es.reset_data_description()

        return combined_es
Combine entityset with another to create a new entityset with the
        combined data of both entitysets.
        
featuretools/entityset/entityset.py