我已经创建了一个虚拟环境并将我的内核更改为与该环境相关联的内核。我知道这些软件包已安装，因为它们可以从命令行正常导入。
运行 !pip install matplotlib 收益：
Requirement already satisfied: matplotlib in ./meme-env/lib/python3.9/site-packages (3.4.1)
Requirement already satisfied: pyparsing>=2.2.1 in ./meme-env/lib/python3.9/site-packages (from matplotlib) (2.4.7)
Requirement already satisfied: python-dateutil>=2.7 in ./meme-env/lib/python3.9/site-packages (from matplotlib) (2.8.1)
Requirement already satisfied: kiwisolver>=1.0.1 in ./meme-env/lib/python3.9/site-packages (from matplotlib) (1.3.1)
Requirement already satisfied: numpy>=1.16 in ./meme-env/lib/python3.9/site-packages (from matplotlib) (1.20.2)
Requirement already satisfied: cycler>=0.10 in ./meme-env/lib/python3.9/site-packages (from matplotlib) (0.10.0)
Requirement already satisfied: pillow>=6.2.0 in ./meme-env/lib/python3.9/site-packages (from matplotlib) (8.2.0)
Requirement already satisfied: six in ./meme-env/lib/python3.9/site-packages (from cycler>=0.10->matplotlib) (1.15.0)
然后，当我运行 import matplotlib.pyplot as plt 时，我得到：
ModuleNotFoundError: No module named 'matplotlib'。
我正在运行 Python 3.9.4。