报错：

>conda install python==3.5
Channels:
 - defaults
Platform: win-64
Collecting package metadata (repodata.json): done
Solving environment: failed

PackagesNotFoundError: The following packages are not available from current channels:

  - python==3.5

Current channels:

  - defaults

To search for alternate channels that may provide the conda package you're
looking for, navigate to

    https://anaconda.org

and use the search bar at the top of the page.

解决方法：

conda config --remove-key channels
conda config --add channels https://repo.continuum.io/pkgs/free/ 
conda config --add channels https://repo.continuum.io/pkgs/main/ 
conda config --set show_channel_urls yes

参考文章：Anaconda创建虚拟环境报错 UnavailableInvalidChannel: HTTP 404 NOT FOUND for channel simple <https://pypi.tuna.tsinghua.edu.cn/simple> - LittleDuo - 博客园 (cnblogs.com)