pandas线性插值报错：ValueError: Invalid fill method. Expecting pad (ffill) or backfill (bfill). Got linear

问题遇到的现象和发生背景

对某个数据集读取的dataframe进行线性插值。

问题相关代码，请勿粘贴截图

dataframe的格式是：date列、整型列

def search_none(df,date_index):
    list_1 = []  # 存储生成的
    list_2 = []  # 存储df的
    day = pd.DataFrame(date_index, columns=['date'])
    for d in range(len(day)):
        # day['date'][d] = day['date'][d].strftime('%Y-%m-%d')
        list_1.append(day['date'][d])
    for i in range(len(df)):
        list_2.append(df['date'][i])
    lack = []
    for j in range(len(list_1)):
        if list_1[j] not in list_2:
            lack.append(list_1[j])
    print("缺少价格的天数：", len(lack))
    # print("具体是：\n", lack)

def fix_none(df,date_index):
    # 寻找缺失值
    search_none(df.copy(), date_index)
    df.set_index('date', inplace=True)
    df = df.reindex(date_index)
    df.reset_index(inplace=True)
    df.rename(columns={'index': 'date'}, inplace=True)
    print(df)
    # 进行线性插值填充---------------------报错
    df.interpolate(method='linear', inplace=True)
    # df.interpolate(method='nearest', inplace=True)
    print(df)
    # sys.exit()


def transfor(path,col,to_path):
    df = pd.read_excel(path)
    df.columns = col
    # 对时间序列中的不存在的日期进行填充，防止月度数据出现偏小---------------------------------------
    date_index = pd.date_range(start='20161130', end='20211223', freq='D')
    df1 = df[['date','GZ_maize_prince']]
    # sys.exit()
    #修复缺失值
    df_new = fix_none(df1, date_index)
    print(df_new)

运行结果及报错内容

报错内容：

  File "E:/Users/Administrator/Desktop/chicken_price_predict/data/original_factory/Uncleaned_data/转换.py", line 62, in transfor
    df_new = fix_none(df1, date_index)
  File "E:/Users/Administrator/Desktop/chicken_price_predict/data/original_factory/Uncleaned_data/转换.py", line 45, in fix_none
    df.interpolate(method='linear', inplace=True)
  File "C:\Users\Administrator\anaconda3\envs\tf2\lib\site-packages\pandas\util\_decorators.py", line 311, in wrapper
    return func(*args, **kwargs)
  File "C:\Users\Administrator\anaconda3\envs\tf2\lib\site-packages\pandas\core\frame.py", line 10720, in interpolate
    **kwargs,
  File "C:\Users\Administrator\anaconda3\envs\tf2\lib\site-packages\pandas\core\generic.py", line 6908, in interpolate
    **kwargs,
  File "C:\Users\Administrator\anaconda3\envs\tf2\lib\site-packages\pandas\core\internals\managers.py", line 377, in interpolate
    return self.apply("interpolate", **kwargs)
  File "C:\Users\Administrator\anaconda3\envs\tf2\lib\site-packages\pandas\core\internals\managers.py", line 327, in apply
    applied = getattr(b, f)(**kwargs)
  File "C:\Users\Administrator\anaconda3\envs\tf2\lib\site-packages\pandas\core\internals\blocks.py", line 1369, in interpolate
    new_values = values.fillna(value=fill_value, method=method, limit=limit)
  File "C:\Users\Administrator\anaconda3\envs\tf2\lib\site-packages\pandas\core\arrays\_mixins.py", line 219, in fillna
    value, method, validate_scalar_dict_value=False
  File "C:\Users\Administrator\anaconda3\envs\tf2\lib\site-packages\pandas\util\_validators.py", line 372, in validate_fillna_kwargs
    method = clean_fill_method(method)
  File "C:\Users\Administrator\anaconda3\envs\tf2\lib\site-packages\pandas\core\missing.py", line 120, in clean_fill_method
    raise ValueError(f"Invalid fill method. Expecting {expecting}. Got {method}")
ValueError: Invalid fill method. Expecting pad (ffill) or backfill (bfill). Got linear

如何解决这个问题呢？

已经解决！

将date列置为index列即可，该函数只需要输入目标列。