pip升級的錯誤

AttributeError: ‘NoneType’ object has no attribute ‘bytes’

在PyCharm創建的Virtualenv環境下，使用pip安裝包時，老是提示需要升級pip，具體提示信息為：

You are using pip version 10.0.1, however version 19.1 is available.
You should consider upgrading via the 'python -m pip install --upgrade pip' command.

而當執行完 python -m pip install --upgrade pip 后確報如下錯誤：

AttributeError: 'NoneType' object has no attribute 'bytes'

解決方法如下:

#這個方法我試了是可以的
1、python -m pip install -U --force-reinstall pip 

2、python -m pip install -U pip

3、easy_install -U pip