code: def preprocess(df, stock_list):
      df = df[["open", "high", "low", "close", "volume"]]
      if_first_time = True
      for stock in stock_list:
          if if_first_time:
              ary = df.loc[stock].values
              if_first_time = False
          else:
              temp = df.loc[stock].values
              ary = np.hstack((ary, temp))
      return ary
  
imports: from __future__ import annotations
  import numpy
label_desc: Use image node_id 3 for calling the QuantConnectEngineer obj's underlying member method code with example usage: obj.preprocess(df, stock_list) and returns: ary