问运行一段之前可以运行的代码，python 3 报错，不知道为什么？

Traceback (most recent call last):

File "C:\Users\admin\Anaconda3\lib\site-packages\pandas\core\indexes\base.py", line 3078, in get_loc

return self._engine.get_loc(key)

File "pandas\_libs\index.pyx", line 140, in pandas._libs.index.IndexEngine.get_loc

File "pandas\_libs\index.pyx", line 162, in pandas._libs.index.IndexEngine.get_loc

File "pandas\_libs\hashtable_class_helper.pxi", line 1492, in pandas._libs.hashtable.PyObjectHashTable.get_item

File "pandas\_libs\hashtable_class_helper.pxi", line 1500, in pandas._libs.hashtable.PyObjectHashTable.get_item

KeyError: 'city_id'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):

File "C:\Users\admin\Desktop\我去年买了个表\毕设\city_detail.py", line 93, in <module>

class Schedule(object):

File "C:\Users\admin\Desktop\我去年买了个表\毕设\city_detail.py", line 94, in Schedule

c = city_detail_deal()

File "C:\Users\admin\Desktop\我去年买了个表\毕设\city_detail.py", line 13, in __init__

self.id = df['city_id']

File "C:\Users\admin\Anaconda3\lib\site-packages\pandas\core\frame.py", line 2688, in __getitem__

return self._getitem_column(key)

File "C:\Users\admin\Anaconda3\lib\site-packages\pandas\core\frame.py", line 2695, in _getitem_column

return self._get_item_cache(key)

File "C:\Users\admin\Anaconda3\lib\site-packages\pandas\core\generic.py", line 2489, in _get_item_cache

values = self._data.get(item)

File "C:\Users\admin\Anaconda3\lib\site-packages\pandas\core\internals.py", line 4115, in get

loc = self.items.get_loc(item)

File "C:\Users\admin\Anaconda3\lib\site-packages\pandas\core\indexes\base.py", line 3080, in get_loc

return self._engine.get_loc(self._maybe_cast_indexer(key))

File "pandas\_libs\index.pyx", line 140, in pandas._libs.index.IndexEngine.get_loc

File "pandas\_libs\index.pyx", line 162, in pandas._libs.index.IndexEngine.get_loc

File "pandas\_libs\hashtable_class_helper.pxi", line 1492, in pandas._libs.hashtable.PyObjectHashTable.get_item

File "pandas\_libs\hashtable_class_helper.pxi", line 1500, in pandas._libs.hashtable.PyObjectHashTable.get_item

KeyError: 'city_id'