我的python版本有问题。我直接从站点下载并安装了最新版本的 python，3.9.0，但是当我使用 python --version 命令从终端检查版本时，安装了 2.7.16 并安装了 PIP 包管理器，我得到了这个回复：
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.
Defaulting to user installation because normal site-packages is not writeable
Collecting pip
Downloading pip-20.2.4-py2.py3-none-any.whl (1.5 …