Develop Reference

Linux terminal and Python are mushed together

When I run some commands, which work, for example neofetch, it gives me a Python error.
username#host:~$ as
Traceback (most recent call last):
File "/usr/lib/command-not-found", line 28, in <module>
from CommandNotFound import CommandNotFound
File "/usr/lib/python3/dist-packages/CommandNotFound/CommandNotFound.py", line 19, in <module>
from CommandNotFound.db.db import SqliteDatabase
File "/usr/lib/python3/dist-packages/CommandNotFound/db/db.py", line 5, in <module>
import apt_pkg
ModuleNotFoundError: No module named 'apt_pkg'
It does that whenever I type an invalid command. This started happening after I installed Python 3.9. I am running Kubuntu with Python 3.10 installed by default.

Modern Linux distributions tend to use a lot of python scripts for internal use; for this reason python gets installed with a plethora of libraries.
The error you are getting is because you replaced that fairly complete system python with a version of your own choosing without providing all the libraries the original came with.
The error you see is emitted by /usr/lib/command-not-found, a script using python3 as found in the system path.
I strongly recommend that you re-install the original python packages and use e.g. anaconda for your specific python needs.
The main takeaway from this is:
DON'T MESS WITH THE SYSTEM PYTHON.

try to find which python are you using using which python and uninstall the first python interpreter it finds.

ModuleNotFoundError, even after pip install

I have recently bought a new laptop and was viewing some python projects of mine which I made on my pc. For one of them I use the python-bitvavo-api library which I installed using pip3 install python-bitvavo-api. The version I installed is 1.2.2 which is the latest on their website.
Now when I try to import it using this code: from python_bitvavo_api.bitvavo import Bitvavo, I get the following error:
Traceback (most recent call last):
File "C:\Users\indig\OneDrive\Documenten\Python Projects\Personal\Cryptone\Cryptone.py", line 6, in <module>
from python_bitvavo_api.bitvavo import Bitvavo
ModuleNotFoundError: No module named 'python_bitvavo_api'
I read online that it may occur when using multiple python versions, Im only using 1 and thats python 3.7
Btw. I have the same error with the Pillow module, so it might be a setting in visual studio that I dont know of. Anyway, someone please help. If you need more details please ask.

How are you running it? From the terminal or from VS?
You can also check the installed libraries running the command pip list

Arrow keys not working with Enthought python

If I use the arrow keys in either python or ipython, I don't get what I should, but instead a weird combination of characters: everything is like in this thread, except that I never compiled python from source.
What happened is roughly this: for some mysterious reasons that nobody was able to decipher (see this thread on ubuntuforums), my Kubuntu user stopped working properly and I had to set up a new one. On this new users, I didn't have Enthought python, so I performed (I hope) a global installation of it - and Canopy.
On this python, the arrow keys don't work.
Can you please help me? Please be patient, I'm a beginner...
Thanks in advance!
EDIT: output of python -c 'import readline':
Traceback (most recent call last):
File "", line 1, in
ImportError: No module named readline
EDIT2: Inspired by your comments, I tried the following
/usr/local/Canopy_32bit/User/bin/python setup.py install
for the readline module: it worked!!!
I couldn't get rid of Enthought python as I need all of the packages for scientific computation. Thanks a lot guys, you helped!

If running the command python -c 'import readline' gives you the following output:
Traceback (most recent call last):
File "<string>", line 1, in <module>
ImportError: libreadline.so.5: cannot open shared object file: No such file or directory
then you need to install the older libreadline in your system. On Ubuntu/Kubuntu it is libreadline5 , on Fedora it is compat-readline5

I don't have enough reputation to comment, so I have to put this in as an answer, but when installing Enthought did you by any chance replace your original python install on your machine? I vaguely remember the install script asking me whether I wanted to make Enthought my default python install.
You might still need to rebuild your Python as posted in the original question that you linked.

Conflicting versions of python in ubuntu

So i had python 2.7.2 on my server and i needed to update it to python 2.7.3. So i've tried to remove the 2.7.2 version and then install the new one using the sources. I wasn't able to remove the 2.7.2 version cause the system uses it to run crucial services on server, so i installed the 2.7.3 version in hope that after that i would be able to remove the old version. Still i cant remove the old version, although i'm able to execute the python 2.7.3 when i install any module i cant import it. I added the path to sys.path and i started finding the module but importing it causes another errors.
My python executes the /usr/local/bin/python which is the 2.7.3 version where the problems are.
If i try to execute python like this /usr/bin/python it executes the old version and everything works fine there, i can import the new installed modules.
So what can i do to make python 2.7.3 work?
I've searched a lot of tutorials and tried things like add the library in .pth files on python and i started finding the modules but when importing it i get errors like this:
>>> import numpy
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python2.7/dist-packages/numpy/__init__.py", line 137, in <module>
import add_newdocs
File "/usr/local/lib/python2.7/dist-packages/numpy/add_newdocs.py", line 9, in <module>
from numpy.lib import add_newdoc
File "/usr/local/lib/python2.7/dist-packages/numpy/lib/__init__.py", line 4, in <module>
from type_check import *
File "/usr/local/lib/python2.7/dist-packages/numpy/lib/type_check.py", line 8, in <module>
import numpy.core.numeric as _nx
File "/usr/local/lib/python2.7/dist-packages/numpy/core/__init__.py", line 5, in <module>
import multiarray
ImportError: /usr/local/lib/python2.7/dist-packages/numpy/core/multiarray.so: undefined symbol: PyUnicodeUCS4_AsUnicodeEscapeString
Thanks for the help
EDIT PROBLEM SOLvED
So to solve the missing import modules i created a .pth file under /usr/local/lib/python2.7/site-packages/ with the directories where the python modules are and the python starts to find them.
To fix the comptability problems you can install python from sources and specify the unicode doing ./configure --enable-unicode
more information here

Do not EVER mess with system python, EVER.
What you should do is install python 2.7.3 with a --prefix into your home directory, then use virtualenv -p /home/myuser/path/to/python.
In any case, using virtualenv to run your own application is almost always a good idea, as it avoids polluting the system package directories with libraries you use in your own applications.

It looks like the modules you've installed were built against your old version of Python, or at least a version incompatible with your newer installation. The import error you're seeing at the bottom is the numpy module searching for a symbol that is not in your build of 2.7.3. There is further information here.
If possible, it's usually way easier to upgrade Python with a package manager. That way, if anything on your system depends on Python, but does not need exactly 2.7.2, then Python can be easily upgraded without disturbing anything. I'm guessing that either your server doesn't have a newer version of Python available and you can't add new repositories, or you don't have access to a package manager. If using packages is possible, I would go ahead and remove what you've built from source (the command should be 'make clean' if Python uses GNU Make).
If that isn't an option, then there should be a way to compile Python, but not install it into system directories. Then you could add a symlink for users, and make sure that symlink has precedence in their path.

When installing python use the following steps
using prefix to specify the installation directory
./configure --prefix=/usr/bin/python
make
make install
Then everytime u run a new Terminal u have specify
export PATH="$PATH:/usr/bin/"
to tell where is the installation directory of Python
This way u can use any number of pythons

You can install python libs from R. It works for me.
For example, to install numpy library from R type:
system('python -m pip install -U numpy')

Modules in Python on Windows

I have a simple sode snippet that uses cairomodule. I would like to launch the scipt but it somehow cannot run giving this error :
Traceback (most recent call last):
File "C:\Users\xxx\Desktop\test.py", line 1, in <module>
import cairo
ImportError: No module named cairo
how should I "install" a module in Python on Windows ? I have tried installing http://gladewin32.sourceforge.net/ as stated on cairo page that I can get cairo as a "side effect" of intalling GTK+ but somehow this didn't work.
If I should add some paths to PATH please indicate which one as I am raelly confused about this.
Now I realise how simpler that would be on linux with powerful terminal :)

Try installing PyGtk from here: http://www.pygtk.org/downloads.html. The all-in-one-installer worked for me. Just choose the packages you want installed.