In #45597 the error was "no destroot found". The cause was the user did not clean before trying again.
This is not the same as your issue, which is "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/requests/__init__.py already exists and does not belong to a registered port".
Why does that file already exist, if it was not provided by a MacPorts port? You can try forcing the port activation, but if you cannot explain why the file already existed, who knows how many other files already exist that should not be there. In that case the safest solution would be to uninstall MacPorts and all ports, then remove /opt/local (after saving any important files, such as configuration files, data files, databases), then reinstall the ports you want.
