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.

Update: Installing latest version of gcc 9: (gcc 9.3.0) - released March 12, 2020:

Same method can be applied to gcc 10 (gcc 10.1.0) - released May 7, 2020

Download file: gcc-9.3.0.tar.gz or gcc-10.1.0.tar.gz

Compile and install:

//required libraries: (some may already have been installed)
dnf install libmpc-devel mpfr-devel gmp-devel

//if dnf install libmpc-devel is not working try:
dnf --enablerepo=PowerTools install libmpc-devel

//install zlib
dnf install zlib-devel*

./configure --with-system-zlib --disable-multilib --enable-languages=c,c++

make -j 8 <== this may take around an hour or more to finish
              (depending on your cpu speed)

make install

Tested under CentOS 7.8.2003 for gcc 9.3 and gcc 10.1

Tested under CentOS 8.1.1911 for gcc 10.1 (may take more time to compile)

Results: gcc/g++ 9.3.0/10.1.0

Installing gcc 7.4 (gcc 7.4.0) - released December 6, 2018:

Download file: https://ftp.gnu.org/gnu/gcc/gcc-7.4.0/gcc-7.4.0.tar.gz

Compile and install:

//required libraries:
yum install libmpc-devel mpfr-devel gmp-devel

./configure --with-system-zlib --disable-multilib --enable-languages=c,c++

make -j 8 <== this may take around 50 minutes or less to finish with 8 threads
              (depending on your cpu speed)


make install

Result:

Notes:

1. This Stack Overflow answer will help to see how to verify the downloaded source file.

2. Use the option --prefix to install gcc to another directory other than the default one. The toplevel installation directory defaults to /usr/local. Read about gcc installation options

You may give it a try using the below steps if that may help: Download the latest package from http://ftp.gnu.org/gnu/gcc/gcc-9.2.0/

wget http://ftp.gnu.org/gnu/gcc/gcc-9.2.0/gcc-9.2.0.tar.gz

Extract the files using the steps below:

tar -xzvf gcc-9.20.tar.gz
cd gcc-9.2.0

Build a configuration using the below,

./configure

Compile the installation using make and then make install.

make 
make install 

Permanently adding DTS to your development environment

After installing the devtoolset:

yum install devtoolset-8-gcc devtoolset-8-gcc-c++

You can also use the following command, to make DTS the default:

source scl_source enable devtoolset-8

The benefit of this command is that it can be added to .bashrc, so that you don't have to run the scl command every time you login:

scl enable devtoolset-8 -- bash

One can surely build the gcc on CentOS oneself(though ew!).

Generally follow the below steps:

sudo yum -y update
sudo yum -y install bzip2 wget gcc gcc-c++ gmp-devel mpfr-devel libmpc-devel make
gcc --version
wget http://mirrors-usa.go-parts.com/gcc/releases/gcc-8.2.0/gcc-8.2.0.tar.gz
tar zxf gcc-8.2.0.tar.gz
mkdir gcc-8.2.0-build
cd gcc-8.2.0-build
../gcc-8.2.0/configure --enable-languages=c,c++ --disable-multilib
make -j 2
sudo make install
gcc --version

At this point, many can not see 8.2, i.e.

gcc version 4.8.5 (GCC)

Just overwrite the old gcc with which just built, i.e.

# which gcc
/usr/local/bin/gcc
# cp gcc/xgcc /usr/local/bin/gcc
# gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/aarch64-unknown-linux-gnu/7.2.0/lto-wrapper
Target: aarch64-unknown-linux-gnu
Configured with: ../gcc-7.2.0/configure --enable-languages=c,c++ --disable-multilib
Thread model: posix
gcc version 7.2.0 (GCC)

In order to avoid library error, one may need update libstdc as well,

cp ./aarch64-unknown-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6 /usr/local/lib64/libstdc++.so.6
cp ./stage1-aarch64-unknown-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6 /usr/lib64/libstdc++.so.6

One may also update libc.so as well, i.e. 2.18

curl -O http://ftp.gnu.org/gnu/glibc/glibc-2.18.tar.gz
tar zxf glibc-2.18.tar.gz
cd glibc-2.18/
mkdir build
cd build/
../configure --prefix=/usr
make -j2
make install
ln -sf /usr/glibc-2.18/glibc-2.18.so /lib64/libc.so.6

Finally, type /lib64/libc.so.6 to confirm

Mostly, ln would fail, since old relations, and LD is suggested, i.e.

LD_LIBRARY_PATH=/usr/glibc-2.18/lib
export LD_LIBRARY_PATH