source.list correct ?

Deal all,

I aquiered a Jetson nano few weeks ago and I am in trouble to follow any tutorial because any time I have to install a new package I end up with the following error message. I am starting to think that I have an issue with my source.list file.
How can I be sure of the following things :
1-my source.list file is correctly configured
2-the package I want is available on the source I have configured

Package python3-numpy is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Unable to locate package libpython3-dev
E: Package 'python3-numpy' has no installation candidat

Below example of issues I had but I found out on Ubuntu – Package Search Results -- bionic that they existe for my linux distribution :

Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package hdf5-tools

But I found it : Ubuntu – Details of package hdf5-tools in bionic

Below my source file

See UpgradeNotes - Community Help Wiki for how to upgrade to

newer versions of the distribution.

deb Index of /ubuntu bionic main restricted

deb-src Index of /ubuntu-ports bionic main restricted

Major bug fix updates produced after the final release of the

distribution.

deb Index of /ubuntu bionic-updates main restricted

deb-src Index of /ubuntu-ports bionic-updates main restricted

N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu

team. Also, please note that software in universe WILL NOT receive any

review or updates from the Ubuntu security team.

deb Index of /ubuntu bionic universe

deb-src Index of /ubuntu-ports bionic universe

deb Index of /ubuntu bionic-updates universe

deb-src Index of /ubuntu-ports bionic-updates universe

N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu

team, and may not be under a free licence. Please satisfy yourself as to

your rights to use the software. Also, please note that software in

multiverse WILL NOT receive any review or updates from the Ubuntu

security team.

deb Index of /ubuntu bionic multiverse

deb-src Index of /ubuntu-ports bionic multiverse

deb Index of /ubuntu bionic-updates multiverse

deb-src Index of /ubuntu-ports bionic-updates multiverse

N.B. software from this repository may not have been tested as

extensively as that contained in the main release, although it includes

newer versions of some applications which may provide useful features.

Also, please note that software in backports WILL NOT receive any review

or updates from the Ubuntu security team.

deb Index of /ubuntu bionic-backports main restricted universe multiverse

deb-src Index of /ubuntu-ports bionic-backports main restricted universe multiverse

Uncomment the following two lines to add software from Canonical’s

‘partner’ repository.

This software is not part of Ubuntu, but is offered by Canonical and the

respective vendors as a service to Ubuntu users.

deb Index of /ubuntu bionic partner

deb-src Index of /ubuntu bionic partner

deb Index of /ubuntu-ports bionic-security main restricted universe

deb-src Index of /ubuntu-ports bionic-security main restricted

deb-src Index of /ubuntu-ports bionic-security universe

deb Index of /ubuntu-ports bionic-security multiverse

deb-src Index of /ubuntu-ports bionic-security multiverse

deb Index of /ubuntu-ports bionic main universe multiverse restricted

Thank you in advance for your tips