def cartesian_df(A,B):
    new_df = pd.DataFrame(columns=list(A).extend(list(B)))
    for _,A_row in A.iterrows():
      for _,B_row in B.iterrows():
        row = A_row.append(B_row)
        new_df = new_df.append(row,ignore_index=True)
    return new_df
#这个方法，如果两张表列名重复会出错

def cartesian_df(df_a,df_b):
  '求两个dataframe的笛卡尔积'
  #df_a 复制n次，索引用复制次数
  new_df_a = pd.DataFrame(columns=list(df_a))
  for i in range(0,df_b.shape[0]):
    df_a['merge_index'] = i
    new_df_a = new_df_a.append(df_a,ignore_index=True)
  #df_b 设置索引为行数
  df_b.reset_index(inplace = True, drop =True)
  df_b['merge_index'] = df_b.index
  #merge
  new_df = pd.merge(new_df_a,df_b,on=['merge_index'],how='left').drop(['merge_index'],axis = 1)
  return new_df

#两个原始表中不能有列名'merge_index'