Comment 6 for bug 1192890

TL;DR
The issue for me lied in /etc/bash.bashrc

This line near the bottom:
python /usr/lib/command-not-found -- $1

should be:
/usr/lib/command-not-found -- $1

Long explanation follows:
I had the same issue. For me issue occurred whenever I mistyped a command.

/usr/lib/command-not-found is a python program.

I found that if I ran it like:
python3.3 /usr/lib/command-not-found bad-command
it ran fine, but
python /usr/lib/command-not-found bad-command

Resulted in:
Traceback (most recent call last):
  File "/usr/lib/python3.3/site.py", line 631, in <module>
    main()
  File "/usr/lib/python3.3/site.py", line 616, in main
    known_paths = addusersitepackages(known_paths)
  File "/usr/lib/python3.3/site.py", line 284, in addusersitepackages
    user_site = getusersitepackages()
  File "/usr/lib/python3.3/site.py", line 260, in getusersitepackages
    user_base = getuserbase() # this will also set USER_BASE
  File "/usr/lib/python3.3/site.py", line 250, in getuserbase
    USER_BASE = get_config_var('userbase')
  File "/usr/lib/python3.3/sysconfig.py", line 580, in get_config_var
    return get_config_vars().get(name)
  File "/usr/lib/python3.3/sysconfig.py", line 530, in get_config_vars
    _init_posix(_CONFIG_VARS)
  File "/usr/lib/python3.3/sysconfig.py", line 403, in _init_posix
    from _sysconfigdata import build_time_vars
  File "/usr/lib/python3.3/_sysconfigdata.py", line 6, in <module>
    from _sysconfigdata_m import *
ImportError: No module named '_sysconfigdata_m'

The issue lied in /etc/bash.bashrc

This line near the bottom:
python /usr/lib/command-not-found -- $1

 was invoking python 2.

Changing it to:
python3.3 /usr/lib/command-not-found -- $1

or just plain:
/usr/lib/command-not-found -- $1

fixed the problem for me :)