Python3 no such file or directory - linux

Question

I am trying to make python3 executable scripts and run them from shell.I have python 3.4.0 installed on my system.
So, I added '/home/spandan/python_codes' directory to PYTHONPATH, as I am planning to keep my scripts and modules here.
However, while trying to execute these, the above error is thrown by the system, and the scripts wont execute unless I go into the python_codes directory and then execute them.
Executing python program : Here I found out that PYTHONPATH is irrelevant while making scripts, and also how to set the python shebang. So I set mine as #!/usr/bin/env python3.4.0
Is it correct?

Answer 1

You don't have to put your python codes in a global path. Just make your python 3.4 interpreter interpreter available globally. For that, edit .bash_profile or .bashrc file in your home directory and add the following line:
export PATH=${PATH}:/usr/bin/python3
That will make python3 executable irrespective of your current working directory.
In order to execute code from your codes directory, you just have to write:
$ python3 ./your_code.py
Another way is to add the shebang at the top of your code as
#/usr/bin/python3
and change the permission to executable by the current user (by default it will not have execute permission).
$ chmod 744 your_code.py
and then executing the script directly as
$ your_code.py
I hope I could address your problem.

Answer 2

Another way to do it is to use python-is-python2 or python-is-python3 debian packages with /usr/bin/env python sheabang.
This option will let the end user select which interpreter he want to use while maintaining your code versionless and avoiding some people to install unwanted interpreter versions.
As an example, run this commands to make a sample file:
cat << EOF > version.py && chmod +x version.py
#!/usr/bin/env python
import sys
print(sys.version)
EOF
And run the following command if you want to set python2 as default:
sudo apt install python-is-python2
Or run this command if you want to set python3 as default:
sudo apt install python-is-python3
Finally you could see the python interpreter version that you have been selected by running:
./version.py
The only drawback of this solution is that you could make your python scripts compatible across python interpreter versions, but thats your decision!
You can install which you want and change from python2 to python3 and vice- versa as you want, but the idea is to fix a python interpreter version in a system and not change it again unless definitive upgrade.
References:
https://askubuntu.com/questions/1296790/python-is-python3-package-in-ubuntu-20-04-what-is-it-and-what-does-it-actually