Saving to clipboard in a Python script running as shell command

Question

The following python script successfully copies a given string into the clipboard when run from Ubuntu shell:

import os
text = 'The text to be copied to the clipboard.'
os.system("echo -n {s} | xsel -b".format(s=text))

However, when I execute the script from Emacs as follows, it does not work:

(call-process-shell-command "clipboard.py &" nil 0)

What is special about the script run with call-process-shell-command and how do I work around the problem so my Python script would be able to use the clipboard?

EDIT: In addition, (shell-command-to-string "python clipboard.py") freezes.

Answer 1

Using the -i option of xsel, which tells xsel to read standard input, fixes it. I do not know why it worked without this option outside of Emacs.