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python3.5 sees but python3.9 does not see sqlite3

My machine:
Linux eyes 4.9.0-9-amd64 #1 SMP Debian 4.9.168-1+deb9u3 (2019-06-16) x86_64 GNU/Linux
i.e. python3.5 is its native python3
Have two python3 in the system:
root#machine: # update-alternatives --list python3
/usr/bin/python3.5
/usr/local/bin/python3.9
root#machine: # update-alternatives --config python3
There are 2 choices for the alternative python3 (providing
/usr/bin/python3).
Selection Path Priority Status
---------------------------------------------------------------
0 /usr/local/bin/python3.9 2 auto mode
1 /usr/bin/python3.5 1 manual mode
* 2 /usr/local/bin/python3.9 2 manual mode
+++++++++++ LET'S CHOOSE 1 FIRST +++++++++++
root#machine: # python3
Python 3.5.3 (default, Nov 18 2020, 21:09:16)
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sqlite3 <------------ OK
>>> exit()
**+++++++++++ LET'S CHOOSE 2 NOW +++++++++++++
root#machine: # python3
Python 3.9.0 (default, Nov 23 2020, 09:50:01)
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sqlite3
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python3.9/sqlite3/__init__.py", line 23, in <module>
from sqlite3.dbapi2 import *
File "/usr/local/lib/python3.9/sqlite3/dbapi2.py", line 27, in <module>
from _sqlite3 import *
ModuleNotFoundError: No module named '_sqlite3' <------- WHAT?
>>> exit()
++++++++++++++++++++++++++++++++++++++++++++
root#machine: # head ~/python3-9_distr/Python-3.9.0/config.log
This file contains any messages produced by compilers while
running configure, to aid debugging if configure makes a mistake.
It was created by python configure 3.9, which was
generated by GNU Autoconf 2.69. Invocation command line was
$ ./configure --enable-optimizations --enable-loadable-sqlite-extensions
++++++++++++++++++++++++++++++++++++++++++++
/usr/lib/python3.5/lib-dynload# ls -la _sqlite3.cpython-35m-x86_64-linux-gnu.so
-rw-r--r-- 1 root root 96552 Nov 18 23:09 _sqlite3.cpython-35m-x86_64-linux-gnu.so
BUT /usr/local/lib/python3.9/lib-dynload DID NOT HAVE _sqlite3.*
I copied _sqlite3.cpython-35m-x86_64-linux-gnu.so and renamed to
-rwxr-xr-x 1 root root 96552 Nov 18 23:09 _sqlite3.cpython-3**9**m-x86_64-linux-gnu.so
Nothing had changed.
++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++
How come ? How can I make sqlite3 work in my python3.9 ?
UPDATE:
I have found a "solution". As I mentioned before, I copied
/var/lib/python3.5/lib-dynload/
_sqlite3.cpython-35m-x86_64-linux-gnu.so
and renamed to
/var/local/lib/python3.9/lib-dynload/
_sqlite3.cpython-39m-x86_64-linux-gnu.so
but it did not work.
Then I copied
_sqlite3.cpython-39m-x86_64-linux-gnu.so
to
_sqlite3.so in the same folder (/var/local/lib/python3.9/lib-dynload/)
It seemed to be working but later I got new problem.

Hi after you have installed python3.9 have you checked the PATH variable which python uses?
please go to a terminal and type
~$ python3.6
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.path
You should get something that looks like this
['', '/usr/lib/python38.zip', '/usr/lib/python3.8', '/usr/lib/python3.8/lib-dynload', '/home/jishnu/.local/lib/python3.8/site-packages', '/usr/local/lib/python3.8/dist-packages', '/usr/lib/python3/dist-packages']
Note i'm using python3.8 hence output will be different
Do the same thing for your python3.9 and check if the package you are trying to access is installed in any of these paths.
If you want further help on how to add to path, refer this question
PYTHONPATH on Linux

Move from python 2 to python 3 on Mac

I have both python 2.7.16 and python 3.7.3 on my Macbook air.
I don't use python 2.7.16 so I want to remove it, but I understood that this could break my Mac.
I am frustrated from using python3 and pip3 instead of python and pip is there a way to make all of the python3 commands to be accessed by using python (without 3) instead of python 2 and make python 2 be accessible by using python2?
tnx ahead

(base) shrub$ /usr/bin/py
pydoc python python2.7 pythonw
pydoc2.7 python-config python2.7-config pythonw2.7
Looking in /usr/bin there is a python executable (which when run opens a shell with python3) and a python2.7 executable (which when run opens a shell with python2).
(base) shrub$ python
Python 3.7.4 (default, Aug 13 2019, 15:17:50)
[Clang 4.0.1 (tags/RELEASE_401/final)] :: Anaconda, Inc. on darwin
Type "help", "copyright", "credits" or "license" for more information.
(base) shrub$ python2.7
Python 2.7.10 (default, Feb 22 2019, 21:55:15)
[GCC 4.2.1 Compatible Apple LLVM 10.0.1 (clang-1001.0.37.14)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
Running python scripts with python (python hello.py for example) should default to python3 and running scripts with python2.7 (python2.7 hello.py for example) will run them with python2.
Also there is a script called 2to3 which can help you with converting your python2 code to python3 :)
https://docs.python.org/3.0/library/2to3.html

Did installing Miniconda destroy Python 2.7 on my Mac?

Have I lost Python 2.7 and does Mac OS still need it? If so, how do I fix this?
I'm a longtime Python 3.x user on Mac OS. I wanted to try Miniconda3 to see if I could recommend it to Mac and Windows students (non-CS). Now I when I try $ type -a python3 I get:
python3 is /Applications/miniconda3/bin/python3
python3 is /Library/Frameworks/Python.framework/Versions/3.7/bin/python3
python3 is /Library/Frameworks/Python.framework/Versions/3.7/bin/python3
python3 is /Library/Frameworks/Python.framework/Versions/3.6/bin/python3
python3 is /usr/local/bin/python3
Try $ type -a python2 and get:
-bash: type: python2: not found
Try $ type -a python and get:
python is /Applications/miniconda3/bin/python
python is /usr/bin/python
I used the Miniconda 64-bit (.pkg installer) under Python 3.7 here:
https://docs.conda.io/en/latest/miniconda.html

Type /usr/bin/python and:
Python 2.7.10 (default, Oct 6 2017, 22:29:07)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
Okay, it's all good. Thanks, juanpa.arrivillaga!

"python" command can't find Python2 installation

I have screwed up my python install on my MacOS machine.
Here it is -
REMs-MBP:opt rem$ which python
/usr/bin/python
REMs-MBP:opt rem$ python
-bash: /usr/local/opt/python/libexec/bin/python: No such file or directory
REMs-MBP:opt rem$ which python2
/Library/Frameworks/Python.framework/Versions/2.7/bin/python2
REMs-MBP:opt rem$ python2
Python 2.7.14 (v2.7.14:84471935ed, Sep 16 2017, 12:01:12)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
python2 works fine but default python is not working fine.
How can I fix it?
brew install python by default tries to install python3. I need python2.7 as my default.
Updates:
pip still pointing to python3 installation.
PREMs-MBP:opt prem$ which python
/usr/bin/python
PREMs-MBP:opt prem$ pip
-bash: /usr/local/bin/pip: /usr/local/Cellar/python/3.7.0/bin/python3.7: bad interpreter: No such file or directory

Howto symlink Python to Python2.7 as non-superuser

I am a non-superuser of a linux machine.
Currently it has 2 versions of Python.
When I invoke standard python command it gave version 2.6
$ python
[neversaint#mach71 ~]$ python
Python 2.6.2 (r262:71600, Jan 28 2011, 13:47:39)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
$ which python
/opt/somedir/bin/python
It's only when I invoke with python2.7 it gives the version 2.7
[neversaint#mach71 ~]$ python2.7
Python 2.7.6 (default, Nov 11 2013, 13:13:15)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-1)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
$ which phython2.7
/usr/bin/python2.7
My question is how can I set it such that whenever I call $ python it will give me version 2.7.

You can simlink it into some directory both accessible to your user and in your $PATH. For example if /home/<your-username>/local/bin is in your $PATH then you can do
ln -s /usr/bin/python2.7 /home/<your-username>/local/bin/python
In this example /home/<your-username>/local/bin should be in your path before /usr/bin. If there is no such entry in your $PATH you can add it there:
export PATH=$HOME/local/bin:$PATH
You can also add this line to .bashrc or similar to activate it on shell start.

Use a shell alias, alias python=/usr/bin/python2.7 and then python will execute the result of that alias.

in /usr/bin create symlink to python27 or whatever python version you have
sudo ln -s python2.7 python