Tab completion does not work in python org src

Question

I set up a python org src

#+BEGIN_SRC python :results output
import sys

print(sys.version)
print(sys.version_info)

#+END_SRC

#+RESULTS:
: 3.7.4 (default, Aug 13 2019, 20:35:49) 
: [GCC 7.3.0]
: sys.version_info(major=3, minor=7, micro=4, releaselevel='final', serial=0)

After strike C-' to invoke a code buffer, the tab completion refused to work as intented.

Even though activated the python-mode and lsp-mode

ob-ipython did not work as well.

#+begin_src emacs-lisp :tangle yes :results output
(print (emacs-version))
(print (org-version))
#+end_src

#+RESULTS:
: 
: "GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.11)
:  of 2019-09-23, modified by Debian"
: 
: "9.3"