Python3.6 Pandasを用いたCSVファイルの抽出

###前提・実現したいこと
Python3.6 Pandasを用いて、ファイル”XXX.csv”を読み込み、column”AA”において"BBB"を含むindexを抽出し、”XXX2.csv”として出力したいと考えています。

###発生している問題・エラーメッセージ


C:\Users\mymt_akck\Anaconda3\python.exe C:/Users/mymt_akck/PycharmProjects/untitled/training2.py
Traceback (most recent call last):
  File "C:\Users\mymt_akck\Anaconda3\lib\site-packages\pandas\core\indexes\base.py", line 2442, in get_loc
    return self._engine.get_loc(key)
  File "pandas_libs\index.pyx", line 132, in pandas._libs.index.IndexEngine.get_loc
  File "pandas_libs\index.pyx", line 154, in pandas._libs.index.IndexEngine.get_loc
  File "pandas_libs\hashtable_class_helper.pxi", line 1210, in pandas._libs.hashtable.PyObjectHashTable.get_item
  File "pandas_libs\hashtable_class_helper.pxi", line 1218, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 'AA'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:/Users/mymt_akck/PycharmProjects/untitled/training2.py", line 5, in 
    df1 = df1[df1["AA"] == "BBB"]
  File "C:\Users\mymt_akck\Anaconda3\lib\site-packages\pandas\core\frame.py", line 1964, in getitem
    return self._getitem_column(key)
  File "C:\Users\mymt_akck\Anaconda3\lib\site-packages\pandas\core\frame.py", line 1971, in _getitem_column
    return self._get_item_cache(key)
  File "C:\Users\mymt_akck\Anaconda3\lib\site-packages\pandas\core\generic.py", line 1645, in _get_item_cache
    values = self._data.get(item)
  File "C:\Users\mymt_akck\Anaconda3\lib\site-packages\pandas\core\internals.py", line 3590, in get
    loc = self.items.get_loc(item)
  File "C:\Users\mymt_akck\Anaconda3\lib\site-packages\pandas\core\indexes\base.py", line 2444, in get_loc
    return self._engine.get_loc(self._maybe_cast_indexer(key))
  File "pandas_libs\index.pyx", line 132, in pandas._libs.index.IndexEngine.get_loc
  File "pandas_libs\index.pyx", line 154, in pandas._libs.index.IndexEngine.get_loc
  File "pandas_libs\hashtable_class_helper.pxi", line 1210, in pandas._libs.hashtable.PyObjectHashTable.get_item
  File "pandas_libs\hashtable_class_helper.pxi", line 1218, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 'AA'

Process finished with exit code 1
`

###該当のソースコード

import pandas as pd
df1=pd.read_csv('XXX.csv','low_memory=False',engine='python',encoding='utf-8')
df1 = df1[df1["AA"] == "BBB"]
df1.to_csv("XXX2.csv")

###試したこと

###補足情報(言語/FW/ツール等のバージョンなど
Python3.6　プログラミングは初心者です。