Python 3 not working

Question

I lately installed python 3.5 from the source, but I think I did something wrong during the installation or linking. After this I have problem installing any Ubuntu packages. For example, add-apt-repository doesn't work, even after reinstalling software-properties-common.

$ add-apt-repository 
bash: /usr/bin/add-apt-repository: /usr/bin/python3: bad interpreter: No such file or directory

Also, apt-get install will give me this errors

$ sudo apt-get install libraw-dev
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
  libraw-dev
0 upgraded, 1 newly installed, 0 to remove and 229 not upgraded.
3 not fully installed or removed.
Need to get 382 kB/391 kB of archives.
After this operation, 1,588 kB of additional disk space will be used.
Get:1 http://us.archive.ubuntu.com/ubuntu/ trusty/main libraw-dev amd64 0.15.4-1 [382 kB]
Fetched 382 kB in 0s (651 kB/s)    
Selecting previously unselected package libraw-dev:amd64.
(Reading database ... 295477 files and directories currently installed.)
Preparing to unpack .../libraw-dev_0.15.4-1_amd64.deb ...
Unpacking libraw-dev:amd64 (0.15.4-1) ...
Setting up python3.4 (3.4.3-1ubuntu1~14.04.5) ...
Could not find platform independent libraries <prefix>
Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
Fatal Python error: Py_Initialize: Unable to get the locale encoding
ImportError: No module named 'encodings'
Aborted
dpkg: error processing package python3.4 (--configure):
 subprocess installed post-installation script returned error exit status 134
Setting up python3-commandnotfound (0.3ubuntu12) ...
/var/lib/dpkg/info/python3-commandnotfound.postinst: 6: /var/lib/dpkg/info/python3-commandnotfound.postinst: py3compile: not found
dpkg: error processing package python3-commandnotfound (--configure):
 subprocess installed post-installation script returned error exit status 127
dpkg: error processing package software-properties-common (--configure):
 package is in a very bad inconsistent state; you should
 reinstall it before attempting configuration
Setting up libraw-dev:amd64 (0.15.4-1) ...
Errors were encountered while processing:
 python3.4
 python3-commandnotfound
 software-properties-common
E: Sub-process /usr/bin/dpkg returned an error code (1)

Also, trying to add ppa gives the following error

$ sudo add-apt-repository ppa:dhor/myway
sudo: unable to execute /usr/bin/add-apt-repository: No such file or directory

What's going on, any ideas?

Solution

1. First, you need to restore the core of Python 3:

   sudo apt install -f --reinstall python3 python3.4 python3-minimal python3.4-minimal libpython3.4-minimal
   

   If this doesn't work due to half-installed packages depending on Python 3 download and install them manually:

   cd /tmp
   apt-get download python3 python3.4 python3-minimal python3.4-minimal libpython3.4-minimal
   sudo dpkg -i *python3*.deb
   sudo apt install -f
   

2. Install the debsums package and perform a package sanity check to verify the integrity of the remaining packages and reinstall them if necessary.

Comments

[Ravexina]

What is the output of ls -l /usr/bin/python3 ? and whereis python3?

[user109352]

It gives: ls: cannot access /usr/bin/python3: No such file or directory I don't think python3 exists.

[Ravexina]

what about this command : whereis python3

[Byte Commander]

And this, dear children, is exactly why you don't mess with the Python.

[user109352]

it gives python3: /usr/bin/python3.4 /usr/bin/python3.4m /etc/python3.5 /etc/python3.4 /etc/python3 /usr/lib/python3.4 /usr/lib/python3 /usr/bin/X11/python3.4 /usr/bin/X11/python3.4m /usr/local/bin/python3.5m-config /usr/local/bin/python3.5 /usr/local/bin/python3.5-config /usr/local/bin/python3 /usr/local/bin/python3.5m /usr/local/lib/python3.5 /usr/share/python3 /usr/share/man/man1/python3.1.gz