Executing python program

Question

I have been searching the web for an answer now for quite a while, but this is giving me really headache:

I am using Ubuntu 12.04 and I want to execute a Python script from the terminal without using the full path. So i added /home/kyril/python/scripts/ to the PATH variable through putting the following into ./bashrc:

kyrilpathvariable="/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/kyril/Python/scripts/:/home/kyril/Bash/scripts"

if [ "$kyrilpathvariable" = "$PATH" ]; then
    echo PATH already exported

else

PATH=$PATH:/home/kyril/Python/scripts/
PATH=$PATH:/home/kyril/Bash/scripts/
export PATH

fi

(I know the if clause is not necessary but I did not like to have everything two times in my PATH if I type exec bash.)

Now the problem: this perfectly works for my Bash scripts, so after making them executable via chmod I can just type $ script.sh and it is executed. However if I type $ python3 script.py the following error is raised: python3: can't open file 'script.py': [Errno 2] No such file or directory

if I type in the full path to the script it works. Anybody has an idea what I am doing wrong? Do I have to add the directory to the PYTHONPATH? (As I understood this only helps for importing modules).

Thanks guys!

Answer 1

When invoking python3 directly, python runs the script file you told it to, without using $PATH to find it. PYTHONPATH is irrelevant--that's used for searching for Python modules.

I'm guessing you're having issues with the wrong interpreter getting invoked when you run script.py by itself. I don't know what the first line of your script is, but it should be this:

#!/usr/bin/env python3

Or if you need even finer control:

#!/usr/bin/env python3.2

And for Python 2 scripts:

#!/usr/bin/env python2

Or:

#!/usr/bin/env python2.7

You should check that these executables exist on your system before trying to use them.

Answer 2

I would guess that path variables are ignored when python searches for the input-file. Python starts searching for 'script.py' in the current directory, not knowing that there is a path variable declared for that file, and therefore cannot find it.

Unfortunately I'm not sure how to solve it but maybe someone more experienced with variables can enlighten us?

Answer 3

python3 $(type -P script.py)

Tells Bash to look in the PATH for the executable file and supply its location and name.

For example:

$ type -P script.py
/usr/local/bin/script.py

Answer 4

To avoid duplicate entries in the path, you can do:

for dir in Python Bash; do
  dir_to_add="$HOME/$dir/scripts"
  case ":$PATH:" in
    *:"$dir_to_add":*) ;; # path already contains dir, do nothing
    *) PATH+=":$dir_to_add" ;;
  esac
done