code: def bench_merge(benchmark, dataframe, num_key_cols):
      benchmark(
          dataframe.merge,
          dataframe,
          on=list(dataframe.columns[:num_key_cols]),
      )
  
imports: import string
  import numpy
  import pytest
  import pytest_cases
  from config import cudf, cupy
  from utils import benchmark_with_object
label_desc: Use image node_id 3 for calling a global function with example usage: bench_merge(benchmark, dataframe, num_key_cols) without return types