Ubuntu 18.04にpython3をインストールできません

Ubuntu 18.04を新しくインストールしました。フラスコを実行できるようにPythonをインストールしたいが、何らかの理由で実行するたびに

sudo apt install python3-minimal

続いて、次のような結果が表示されます。

ashoms@ashoms:~$ sudo apt install python3-minimal
[sudo] password for ashoms: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
python3-minimal is already the newest version (3.6.5-3ubuntu1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
3 not fully installed or removed.
Need to get 0 B/53.4 kB of archives.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
dpkg: dependency problems prevent configuration of update-manager:
 update-manager depends on policykit-1; however:
  Package policykit-1 is not installed.

dpkg: error processing package update-manager (--configure):
 dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup error from a previous failure.
                          dpkg: dependency problems prevent configuration of ubuntu-release-upgrader-gtk:
 ubuntu-release-upgrader-gtk depends on update-manager; however:
  Package update-manager is not configured yet.

dpkg: error processing package ubuntu-release-upgrader-gtk (--configure):
 dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup error from a previous failure.
                          Errors were encountered while processing:
 update-manager
 ubuntu-release-upgrader-gtk
E: Sub-process /usr/bin/dpkg returned an error code (1)