code: def prep_skl_df(df, copy_df=False):
      """Make df compatible with sklearn input expectations.
  
      Changes:
      turns column index into a list of strings
  
      Parameters
      ----------
      df : pd.DataFrame
          list of indices to sample from
      copy_df : bool, default=False
          whether to mutate df or return a copy
          if False, index of df is mutated
          if True, original df is not mutated. If index is not a list of strings,
          a copy is made and the copy is mutated. Otherwise, the original df is returned.
      """
      cols = df.columns
      str_cols = cols.astype(str)
  
      if not np.all(str_cols == cols):
          if copy_df:
              df = df.copy()
          df.columns = str_cols
  
      return df
  
label_desc: Use image node_id 1 for calling a global function with example usage: prep_skl_df(df, copy_df) and returns: df