code: def __call__(self, df):
      empty_result = build_empty_df(df.dtypes).melt(
          id_vars=self.id_vars,
          value_vars=self.value_vars,
          var_name=self.var_name,
          value_name=self.value_name,
          col_level=self.col_level,
      )
      self._output_types = [OutputType.dataframe]
      return self.new_tileable(
          [df],
          shape=(np.nan, len(empty_result.columns)),
          dtypes=empty_result.dtypes,
          index_value=parse_index(
              pd.RangeIndex(-1), df.key, df.index_value.key
          ),
          columns_value=parse_index(
              empty_result.columns, store_data=True
          ),
      )
  
imports: import numpy
  import pandas
  from ...None import opcodes
  from ...core import recursive_tile
  from ...serialization.serializables import AnyField, StringField
  from ...utils import calc_nsplits
  from ..operands import DataFrameOperand, DataFrameOperandMixin, OutputType
  from ..utils import build_empty_df, parse_index, standardize_range_index
label_desc: Use image node_id 7 for calling the DataFrameMelt obj's underlying member method code with example usage: obj.__call__(df) and returns: self