Packets need to be adapted to use one or another. 
Many packages need either one or another implementation of requests.
But now they are mutually exclusive, thus preventing some packages from installation.
It is a good idea to be able to pack both of them into python.

apt-get install python3-module-requests
Reading Package Lists... Done
Building Dependency Tree... Done
The following extra packages will be installed:
  python3-module-ndg python3-module-ndg-httpsclient python3-module-urllib3
The following packages will be REMOVED:
  python3-module-yieldfrom.requests
The following NEW packages will be installed:
  python3-module-ndg python3-module-ndg-httpsclient python3-module-requests
  python3-module-urllib3
0 upgraded, 4 newly installed, 1 removed and 1 not upgraded.
Need to get 0B/274kB of archives.
After unpacking 579kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Committing changes...
Preparing...                            ################################ [100%]
Updating / installing...
1: python3-module-ndg-0.4.2-alt1        ################################ [ 20%]
2: python3-module-ndg-httpsclient-0.4.2-################################ [ 40%]
3: python3-module-urllib3-2:1.15.1-alt1 ################################ [ 60%]
4: python3-module-requests-2.12.4-alt3  ################################ [ 80%]
Cleaning up / removing...
5: python3-module-yieldfrom.requests-0.1################################ [100%]
Done.