Enable the software collection in the answer is only effective in the current shell. The scl utility will create a "child-shell" that set the PATH variables properly, so that in the new child-shell, the enabled software collections will be firstly searched. These settings obviously only take effective temporarily in the current shell.

To make it permanently effective, add the command, source /opt/rh/devtoolset-7/enable to the user's profile (~/.bash_profile or ~/.bashrc for RHEL based OS, like CentOS 7). Then, start a new shell and you will have the right tools available.

After execute scl enable devtoolset-7 bash, you will need to execute exit twice to exit the opened shell window, which verifies that the scl command created a new shell instance as a child process. There might be side-effect with creating a child-shell, so do not put this command in the ~/.bashrc profile, otherwise it will repeatedly create child-shell (non-login shell) as each shell will load the profile, resulting in a endless recursive loop. Put it in ~/.bash_profile, it will be loaded for only once (for the login shell), but you will need to exit twice every time.

But for development purpose, scl enable devtoolset-7 bash would be preferred, as you can exit the created child-shell, and then switch between different versions of the same software.

More details about the GCC version in python terminal:

The version info of the built-in Python in CentOS 7:

[root@conda condabuilder]# python
Python 2.7.5 (default, Nov 16 2020, 22:23:17) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)] on linux2
Type "help", "copyright", "credits" or "license" for more information.

The version info of the user installed (via conda) Python on a system even without higher version of GCC installed:

[root@conda condabuilder]# conda activate jupyter
(jupyter) [root@conda condabuilder]# python -VV
Python 3.10.9 | packaged by conda-forge | (main, Feb  2 2023, 20:20:04) [GCC 11.3.0]

From the results, we can see that the GCC version contained in Python's version info is not related to the system's GCC. The system's default Python (2.7.5) should have been compiled with the GCC version distributed with CentOS 7, so the version info show the same GCC version. But for user installed python, the GCC version info actually depends on what version of GCC is used for building and packging the python binary.

Try:

yum group list

To see if yum can find the Development Tools under Available Groups. If it fails, try:

yum clean all
yum group list

And see if it can find it. If it still fails, you might not have the correct mirrors enabled to resolve it.

try the clean command again and then:

yum --disablerepo=\* --enablerepo=base,updates group list

If you can find it. Great! Install with:

yum --disablerepo=\* --enablerepo=base,updates groupinstall "Development Tools"

If not so, can you give us the output of:

yum repolist all

EDIT:

Thank you for the output.

I found an article which state the following: "To install the CentOS Development tools, you will need to be able to connect to your Virtual Server using SSH, and work as the root user."

Try switching to user "root" (if you don't know the root login credentials, you can try sudo su. sudo also might work but I see you already have tried that...) and running the above commands.

Lastly, you can try and enable these "sources" repos:

• CentOS-7 - Base Sources
• CentOS-7 - Extras Sources
• CentOS-7 - Updates Sources

And than running yum update followed by groupinstall.

Let me know if that doesn't work. Good luck!