如何解决Python绘图代码中的KeyError('2019-10')错误？

测试绘图功能时所有图表都报相同错误，同事运行同款代码正常，不确定是缺库还是版本问题。错误出在filter_df = df[fechas[d]].copy()行，提示找不到'2019-10'这个键。

出错代码 #

def sub_plot_weekday(df):
    
    fechas = []
    
    for i in range(len(df.index)):
        date = str(df.index[i])[0:7]
        if date not in fechas: 
            fechas.append(date)
    #print(fechas)       
    
    n_subplots = len(fechas)
    n_col = 2
    n_rows = math.ceil(n_subplots/n_col)
    
    fig = plt.figure(figsize = (20, 12))
    
    for d in range(len(fechas)):
        #Guardamos en una var el df filtrado x fecha
        filter_df = df[fechas[d]].copy()
        #Guardamos en una lista el nombre de cada día para cada "Fecha" y la ponemos en una columna
        #print(filter_df)
        dates = filter_df.index
        name_m = dates[0].strftime("%B")
        list_weekdays = [dates[i].date().strftime("%A") for i in range(len(dates))]
        filter_df['weekday'] = list_weekdays
        # Creamos un df agrupando por día de semana contando eventos 
        grouped_by_weekday = pd.DataFrame(filter_df[['EVENT', 'weekday']][filter_df['EVENT'] != 0].groupby('weekday').count())
        
        days_index = grouped_by_weekday.index.tolist()
        days_values = grouped_by_weekday.EVENT.tolist()
         
        order_day, order_val = reorder_lists(days_index, days_values)
        #Añadimos subplot 
        plt.subplot(n_rows, n_col, d+1)
        plt.title('Number of Operations per Weekday (' + name_m + ' ' +fechas[d][:4] + ')',fontsize= 17)
        plt.bar(order_day, order_val, color = 'purple') #(0.5,0.1,0.5,0.6) 
        #plt.xticks(order_day, rotation=45)
        for i, val in enumerate(order_val):
            plt.text(i, val, int(val), horizontalalignment='center', verticalalignment='bottom', fontdict={'fontweight':500, 'size':12})
        plt.ylim(0,26)
        plt.xticks(order_day, rotation=0)
    fig.tight_layout(pad=2.0)
    plt.show()
sub_plot_weekday(dt1)

错误回溯信息 #

KeyError                                  Traceback (most recent call last)
File ~\AppData\Local\anaconda3\envs\myenv\lib\site-packages\pandas\core\indexes\base.py:3790, in Index.get_loc(self, key)
   3789 try:
-> 3790     return self._engine.get_loc(casted_key)
   3791 except KeyError as err:

File index.pyx:152, in pandas._libs.index.IndexEngine.get_loc()

File index.pyx:181, in pandas._libs.index.IndexEngine.get_loc()

File pandas\_libs\hashtable_class_helper.pxi:7080, in pandas._libs.hashtable.PyObjectHashTable.get_item()

File pandas\_libs\hashtable_class_helper.pxi:7088, in pandas._libs.hashtable.PyObjectHashTable.get_item()

KeyError: '2019-10'

The above exception was the direct cause of the following exception:

KeyError                                  Traceback (most recent call last)
Cell In[11], line 1
----> 1 sub_plot_weekday(dt1)

Cell In[10], line 25, in sub_plot_weekday(df)
     21 #Recoremos cada "fecha" recogida
     23 for d in range(len(fechas)):
     24     #Guardamos en una var el df filtrado x fecha
---> 25     filter_df = df[fechas[d]].copy()
     26     #Guardamos en una lista el nombre de cada día para cada "Fecha" y la ponemos en una columna
     27     #print(filter_df)
     28     dates = filter_df.index

File ~\AppData\Local\anaconda3\envs\myenv\lib\site-packages\pandas\core\frame.py:3896, in DataFrame.__getitem__(self, key)
   3894 if self.columns.nlevels > 1:
   3895     return self._getitem_multilevel(key)
-> 3896 indexer = self.columns.get_loc(key)
   3897 if is_integer(indexer):
   3898     indexer = [indexer]

File ~\AppData\Local\anaconda3\envs\myenv\lib\site-packages\pandas\core\indexes\base.py:3797, in Index.get_loc(self, key)
   3792     if isinstance(casted_key, slice) or (
   3793         isinstance(casted_key, abc.Iterable)
   3794         and any(isinstance(x, slice) for x in casted_key)
   3795     ):
   3796         raise InvalidIndexError(key)
-> 3797     raise KeyError(key) from err
   3798 except TypeError:
   3799     # If we have a listlike key, _check_indexing_error will raise
   3800     #  InvalidIndexError. Otherwise we fall through and re-raise
   3801     #  the TypeError.
   3802     self._check_indexing_error(key)

KeyError: '2019-10'
<Figure size 2000x1200 with 0 Axes>

问题分析与修复 #

核心问题是搞混了行索引和列的用法：你从行索引里提取了日期字符串fechas，但却用df[fechas[d]]去按列名取数据，而你的数据里根本没有叫'2019-10'的列，自然触发KeyError。同事的代码能跑，是因为他的dt1数据结构和你的不一样——他的列名是日期格式，而你的日期存在行索引里。

修复方案：

• 替换错误的过滤代码，改成按行索引筛选对应年月的数据，推荐两种写法：
  1. 简单字符串匹配（如果索引是字符串格式）：

     filter_df = df.loc[df.index.str.startswith(fechas[d])].copy()
     

  2. 规范datetime索引筛选（先把索引转为datetime类型，更可靠）：

     # 先确保索引是datetime类型（放在函数开头）
     df.index = pd.to_datetime(df.index)
     # 筛选对应年月
     year, month = int(fechas[d][:4]), int(fechas[d][5:])
     filter_df = df[(df.index.year == year) & (df.index.month == month)].copy()
     

• 另外，提取fechas的循环代码可以简化，不用手动遍历：

  # 如果索引是字符串
  fechas = df.index.str[:7].unique().tolist()
  # 如果是datetime索引，更规范
  fechas = df.index.to_period('M').astype(str).unique().tolist()
  

内容的提问来源于stack exchange，提问作者Luis Enrique Orozco Villanueva