code: def test_setitem(stream):
      df = cudf.DataFrame({"x": list(range(10)), "y": [1] * 10})
  
      sdf = DataFrame(example=df.iloc[:0], stream=stream)
      stream = sdf.stream
  
      sdf["z"] = sdf["x"] * 2
      sdf["a"] = 10
      sdf[["c", "d"]] = sdf[["x", "y"]]
  
      L = sdf.mean().stream.gather().sink_to_list()
  
      stream.emit(df.iloc[:3])
      stream.emit(df.iloc[3:7])
      stream.emit(df.iloc[7:])
  
      df["z"] = df["x"] * 2
      df["a"] = 10
      df["c"] = df["x"]
      df["d"] = df["y"]
  
      assert_eq(L[-1], df.mean())
  
imports: import json
  import operator
  import numpy
  import pandas
  import pytest
  from dask.dataframe.utils import assert_eq
  from distributed import Client
  from streamz import Stream
  from streamz.dask import DaskStream
  from streamz.dataframe import Aggregation, DataFrame, DataFrames, Series
label_desc: Use image node_id 19 for calling a global function with example usage: test_setitem(stream) without return types