conda: why I can not install pkgs in one environment, while I can install in another? - anaconda

Question

I'm using two environment of conda. I can not intall packages in one env, while I can intall packages in the other environment.
The error massage is: 'solving environment: failed'
system: windows 10 x64
The error msg:
(py3env) C:\>conda install cython
Collecting package metadata (current_repodata.json): done
Solving environment: failed
Collecting package metadata (repodata.json): done
Solving environment: failed
PackagesNotFoundError: The following packages are not available from current channels:
- anaconda/pkgs/free/win-64::protobuf==3.2.0=py36_0 -> libprotobuf==3.2.0
- anaconda/pkgs/free/win-64::tensorflow==1.2.1=py36_0 -> backports.weakref==1.0rc1
- anaconda/pkgs/free/win-64::tensorflow==1.2.1=py36_0 -> bleach==1.5.0
- anaconda/pkgs/free/win-64::tensorflow==1.2.1=py36_0 -> html5lib==0.9999999
Current channels:
- https://repo.anaconda.com/pkgs/main/win-64
- https://repo.anaconda.com/pkgs/main/noarch
- https://repo.anaconda.com/pkgs/r/win-64
- https://repo.anaconda.com/pkgs/r/noarch
- https://repo.anaconda.com/pkgs/msys2/win-64
- https://repo.anaconda.com/pkgs/msys2/noarch
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.
While the success info in another environment:
(py2env) C:\>conda install cython Collecting package metadata (current_repodata.json): done Solving environment: done
## Package Plan ##
environment location: C:\Users\sonic\Anaconda3\envs\py2env
added / updated specs:
- cython
The following packages will be downloaded:
package | build
---------------------------|-----------------
certifi-2019.6.16 | py27_0 151 KB
cython-0.29.11 | py27hc56fc5f_0 2.0 MB
------------------------------------------------------------
Total: 2.1 MB
The following NEW packages will be INSTALLED:
cython pkgs/main/win-64::cython-0.29.11-py27hc56fc5f_0
The following packages will be UPDATED:
certifi anaconda/pkgs/free::certifi-2016.2.28~ --> pkgs/main::certifi-2019.6.16-py27_0
Proceed ([y]/n)?

Answer 1

I think it is because you have packages installed from the "free" channel, but that channel has been removed. So conda is confused about what to do. You should read the blog post anaconda.com/why-we-removed-the-free-channel-in-conda-4-7 and temporarily add the "free" channel back to your configuration as described in that blog by running the command conda config --set restore_free_channel true. After you run that command, you can set the restore free channel back to false if you finished installing the Cython. Thanks for the comments of #darthbith