Repair Ubuntu 18.04 after Python 3.6 Removal

Question

I wanted to upgrade my python versions, and when the update via apt did nothing, I decided I wanted to build the newest versions of Python 2 (2.7.16) and 3 (3.7.2). Before I did that however, I unfortunately decided to remove both of the versions I had (2.7.15~rc1-1, 3.6.7), so I basically destroyed my system. I could build and install the new versions just fine, but when I restarted, the GUI wasn't loading. The boot loader is still working, and I can get in the terminal. But when trying to follow some advice on here (like installing ubuntu-desktop), I discovered that I can't connect to the internet (host names can't be resolved when I try to install packages and I can't ping www.google.com). I tried to use the recovery mode where I enabled networking, but no difference.

Is there any chance I can repair my system? Or is there some way I could use a Ubuntu installation USB stick to reset the system to "factory settings" (same partitions etc. as before), even if I have to delete everything on there? I'm running Windows 10 and Ubuntu 18.04 on dual-boot, and even though the installation process went quite smoothly the first time, I had problems before with dual-booting Windows and Ubuntu on my laptop and now I'm scared I could cause even more damage. I'd be very happy if someone could help me.

Edit#1: It seems like I still have python3.6-minimal installed, apt list --installed | grep 'python' outputs:

libpython-stdlib/bionic,now 2.7.15~rc1-1 amd64 [installed,auto-removable]
libpython2.7/bionic-updates,bionic-security,now 2.7.15~rc1-1ubuntu0.1 amd64 [installed]
libpython2.7-minimal/bionic-updates,bionic-security,now 2.7.15~rc1-1ubuntu0.1 amd64 [installed]
libpython2.7-stdlib/bionic-updates,bionic-security,now 2.7.15~rc1-1ubuntu0.1 amd64 [installed]
libpython3-stdlib/bionic-updates,now 3.6.7-1~18.04 amd64 [installed]
libpython3.6/bionic-updates,now 3.6.7-1~18.04 amd64 [installed]
libpython3.6-minimal/bionic-updates,now 3.6.7-1~18.04 amd64 [installed]
libpython3.6-stdlib/bionic-updates,now 3.6.7-1~18.04 amd64 [installed]
python-apt-common/bionic-updates,bionic-updates,now 1.6.3ubuntu1 all [installed]
python-minimal/bionic,now 2.7.15~rc1-1 amd64 [installed,auto-removable]
python-talloc/bionic,now 2.1.10-2ubuntu1 amd64 [installed]
python2.7/bionic-updates,bionic-security,now 2.7.15~rc1-1ubuntu0.1 amd64 [installed]
python2.7-minimal/bionic-updates,bionic-security,now 2.7.15~rc1-1ubuntu0.1 amd64 [installed,automatic]
python3-minimal/bionic-updates,now 3.6.7-1~18.04 amd64 [installed]
python3.6/bionic-updates,now 3.6.7-1~18.04 amd64 [installed]
python3.6-minimal/bionic-updates,now 3.6.7-1~18.04 amd64 [installed]

Also ls /var/cache/apt/archive | grep 'python' gives me:

python3-apt_1.6.3ubuntu1_amd64.deb
python3-distupgrade_1%3a18.04.30_all.deb
python3-gi_3.26.1-2ubuntu1_amd64.deb
python3-gi-cairo_3.26.1-2ubuntu1_amd64.deb
python3-update-manager_1%3a18.04.11.9_all.deb
python-apt-common_1.6.3ubuntu1_all.deb

I hope this helps.

Edit#2: Session log from /var/log/apt/term.log:

Log started: 2019-03-13  23:31:26
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Removing gnome-software-plugin-snap (3.28.1-0ubuntu4.18.04.8) ...
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Removing apturl (0.5.2ubuntu14.2) ...
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Removing foomatic-db-compressed-ppds (20180306-1) ...
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Removing update-notifier (3.192.1.5) ...
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Removing ubuntu-release-upgrader-gtk (1:18.04.30) ...
[1mdpkg:[0m aptdaemon: dependency problems, but removing anyway as you requested:
 python3-aptdaemon depends on aptdaemon.

Removing aptdaemon (1.1.1+bzr982-0ubuntu19) ...
[1mdpkg:[0m python3-aptdaemon: dependency problems, but removing anyway as you requested:
 python3-aptdaemon.gtk3widgets depends on python3-aptdaemon (= 1.1.1+bzr982-0ubuntu19).

Removing python3-aptdaemon (1.1.1+bzr982-0ubuntu19) ...
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Removing ibus-table (1.9.14-3) ...
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[1mdpkg:[0m [1;33mwarning:[0m while removing hplip-data, directory '/usr/share/hplip/ui5' not empty so not removed
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[1mdpkg:[0m [1;33mwarning:[0m while removing hplip-data, directory '/usr/share/hplip/pcard' not empty so not removed
[1mdpkg:[0m [1;33mwarning:[0m while removing hplip-data, directory '/usr/share/hplip/installer' not empty so not removed
[1mdpkg:[0m [1;33mwarning:[0m while removing hplip-data, directory '/usr/share/hplip/fax' not empty so not removed
[1mdpkg:[0m [1;33mwarning:[0m while removing hplip-data, directory '/usr/share/hplip/copier' not empty so not removed
[1mdpkg:[0m [1;33mwarning:[0m while removing hplip-data, directory '/usr/share/hplip/base/pexpect' not empty so not removed
Removing ubuntu-standard (1.417) ...
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[1mdpkg:[0m [1;33mwarning:[0m while removing update-manager-core, directory '/var/lib/update-manager' not empty so not removed
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update-initramfs: deferring update (trigger activated)
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Removing python3-aptdaemon.gtk3widgets (1.1.1+bzr982-0ubuntu19) ...
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Removing usb-creator-gtk (0.3.5) ...
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Removing python3-debian (0.1.32) ...
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Removing python3-debconf (1.5.66) ...
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Removing python3-mako (1.0.7+ds1-1) ...
Removing python3-markupsafe (1.0-1build1) ...
Removing python3-netifaces (0.10.4-0.1build4) ...
Removing python3-oauth (1.0.1-5) ...
Removing python3-olefile (0.45.1-1) ...
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Removing python3-reportlab (3.4.0-3build1) ...
Removing python3-pil:amd64 (5.1.0-1) ...
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Removing python3-renderpm:amd64 (3.4.0-3build1) ...
Removing python3-reportlab-accel:amd64 (3.4.0-3build1) ...
Removing python3-rfc3339 (1.0-4) ...
Removing python3-simplejson (3.13.2-1) ...
Removing python3-software-properties (0.96.24.32.7) ...
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Skip stopping firewall: ufw (not enabled)
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Removing python3-idna (2.6-1) ...
Removing python3-pkg-resources (39.0.1-2) ...
Removing python3-urllib3 (1.22-1) ...
Removing python3-six (1.11.0-2) ...
Removing python3-distupgrade (1:18.04.30) ...
Removing python3-update-manager (1:18.04.11.9) ...
Removing lsb-release (9.20170808ubuntu1) ...
Removing python3-apt (1.6.3ubuntu1) ...
[1mdpkg:[0m gir1.2-ibus-1.0:amd64: dependency problems, but removing anyway as you requested:
 gnome-shell depends on gir1.2-ibus-1.0 (>= 1.5.2); however:
  Package gir1.2-ibus-1.0:amd64 is to be removed.

Removing gir1.2-ibus-1.0:amd64 (1.5.17-3ubuntu4) ...
[1mdpkg:[0m python3: dependency problems, but removing anyway as you requested:
 gnome-shell depends on python3; however:
  Package python3 is to be removed.

Removing python3 (3.6.7-1~18.04) ...
[1mdpkg:[0m gnome-shell: dependency problems, but removing anyway as you requested:
 network-manager-gnome depends on policykit-1-gnome | polkit-1-auth-agent; however:
  Package policykit-1-gnome is not configured yet.
  Package polkit-1-auth-agent is not installed.
  Package policykit-1-gnome which provides polkit-1-auth-agent is not configured yet.
  Package gnome-shell which provides polkit-1-auth-agent is to be removed.

Removing gnome-shell (3.28.3-0ubuntu0.18.04.4) ...
Processing triggers for mime-support (3.60ubuntu1) ...
Processing triggers for libreoffice-common (1:6.0.7-0ubuntu0.18.04.2) ...
Processing triggers for desktop-file-utils (0.23-1ubuntu3.18.04.2) ...
Processing triggers for libglib2.0-0:amd64 (2.56.3-0ubuntu0.18.04.1) ...
Processing triggers for cups (2.2.7-1ubuntu2.3) ...
Processing triggers for initramfs-tools (0.130ubuntu3.7) ...
update-initramfs: Generating /boot/initrd.img-4.15.0-46-generic
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Setting up policykit-1-gnome (0.105-6ubuntu2) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Processing triggers for shared-mime-info (1.9-2) ...
Processing triggers for dbus (1.12.2-1ubuntu1) ...
Processing triggers for hicolor-icon-theme (0.17-2) ...
Log ended: 2019-03-13  23:32:0

I can see now that a bunch of really important packages got removed. And by the looks of my bash history, it seems I called both sudo apt remove python and sudo apt remove python3 even before building the newer versions. I changed my original question to reflect that.

Answer 1

I solved the issue by reinstalling Ubuntu as suggested (thank you!).

When I first installed Ubuntu, I followed exactly the advice from Dual Boot Windows 10 and Linux Ubuntu on Separate Hard Drives [duplicate].

I still had the USB installation medium, so I booted from it, chose 'Something else' and then I had only three changes to make (Ubuntu was installed on partition /dev/sdd):

• set sdd2 to be used as ext4 file system (instead of 'don't use this partition') and set '/' as mount
• set sdd4 to be used as ext4 file system (instead of 'don't use this partition') and set '/home' as mount
• set sdd1 to be used for the boot loader in the drop-down list

So in summary I just had to redo part of the settings I used for my initial installation, and I didn't have to create the partition table first etc. I made sure not to select the 'format partition' option anywhere, so when the installation was done, all my files where still there. Thank you for your help everyone!