我曾经使用virtualenv创建不同的项目环境，相同的库（不同版本）。最近，我安装了Anaconda来进行一些机器学习。当我尝试使用virtualenv创建新环境时，出现以下错误：
(venv) usr@KC-SCE:~/Desktop/bTree$ pip install nltk
Requirement already satisfied: nltk in /home/usr/anaconda3/lib/python3.6/site-packages (3.3)
Requirement already satisfied: six in /home/usr/anaconda3/lib/python3.6/site-packages (from nltk) (1.11.0)
tensorflow-tensorboard 1.5.1 has requirement bleach==1.5.0, but you'll have bleach 2.1.3 which is incompatible.
tensorflow-tensorboard 1.5.1 has requirement html5lib==0.9999999, but you'll have html5lib 1.0.1 which is incompatible.
tensorboard 1.8.0 has requirement bleach==1.5.0, but you'll have bleach 2.1.3 which is incompatible.
tensorboard 1.8.0 has requirement html5lib==0.9999999, but you'll have html5lib 1.0.1 which is incompatible.
jupyterlab 0.32.1 has requirement jupyterlab_launcher<0.11.0,>=0.10.0, but you'll have jupyterlab-launcher 0.11.0 which is incompatible.
我不明白的是为什么我无法下载已经存在的库！我可能会在其他版本中使用它。