Installing pythonstartup file

Question

How do I install the pythonstartup file so that it runs on command like python myfile.py?

I tried to install it into my /home/myuser directory for Ubuntu, but it said that I had insufficient permissions. Furthermore, different places say alternately that it should be in all caps or in all lower case with a period before it. The Python command line guide does not seem to explain where to put the file, or how to change which environment variable to 'point' to it.

Answer 1

In your ~/.bashrc:

export PYTHONSTARTUP=$HOME/.pythonstartup

and put your python code in $HOME/.pythonstartup, like:

import rlcompleter
import readline

readline.parse_and_bind("tab: complete")

Then run the interactive shell:

python

See the imports from PYTHONSTARTUP are processed. This only works in python interactive mode.

For more information about PYTHONSTARTUP variable, read the python man page:

$ man python

Answer 2

How to execute the python file defined in $PYTHONSTARTUP when you execute a file like python foobar.py

Run this command to find out where your OS has defined USER_SITE:

$ python -c "import site; site._script()" 

Mine says:

USER_SITE: '/home/el/.local/lib64/python2.7/site-packages'

Create a new file there called /home/el/.local/lib64/python2.7/site-packages/usercustomize.py, put this code in there:

try:
    import your_things
    import readline
    print("ROCKETMAN!")

except ImportError:
    print("Can't load your things")
    print("Either exit here, or perform remedial actions")
    exit()

Close the terminal and reopen it to clear out any shenanigans.

Make a new file python foobar.py anywhere on the filesystem, put this code in there:

#Note there is no your_things module imported here.
#Print your_things version:
print(your_things.__version__)

Run it:

python foobar.py 
ROCKETMAN!
'1.12.0'

What just happened.

You used the python sitewide specific python configuration hook and imported libraries in the usercustomize.py file which ran before foobar.py.

Documentation: https://docs.python.org/2/library/site.html

Where I found this trick: https://nedbatchelder.com/blog/201001/running_code_at_python_startup.html