improve installing python3 on ubuntu

docs/posts/2019/2019-10-27-installing-python3-on-ubuntu.md

@@ -16,79 +16,27 @@ Most of tutorials on the Internet about installing Python3.6 on Ubuntu are by [u
 
 <!-- more -->
 
-## Installing Python3.6 on Ubuntu 16.04
-
-### Disabling IPv6
+## Disabling IPv6
 
 IPv6 is enabled by default on Ubuntu 16.04, in some cases, your Ubuntu network connection might be very low due to IPv6. Use `ip a | grep inet6` to check if IPv6 is enabled.
 
 Ref: [How to disable ipv6 address on ubuntu 18 04 bionic beaver linux](https://linuxconfig.org/how-to-disable-ipv6-address-on-ubuntu-18-04-bionic-beaver-linux)
 
 To disable IPv6 in a persist way, add following 2 lines in the file `/etc/sysctl.conf` and [reload the sysctl by `sudo sysctl --system`](https://www.cyberciti.biz/faq/reload-sysctl-conf-on-linux-using-sysctl/) or reboot the server:
 
-```
+```bash
 net.ipv6.conf.all.disable_ipv6=1
 net.ipv6.conf.default.disable_ipv6=1
 ```
 
-### Installing build packages
-
-```bash
-sudo apt install -y build-essential zlib1g-dev libssl-dev
-```
-
-!!! note
-
-    without `libssl-dev` package, pip install will throw TLS/SSL error.
-
-!!! note
-
-    From this point of view, installing Python on Windows by Scoop is much more pleasant :)
-
-### Installing Python3.6 from official source
-
-The latest Python3.6 version at the time of this writing is 3.6.9.
-
-```bash
-# You may download the Python source to a local shared location (S3 or Artifactory, etc.) if you need to deploy Python to many servers.
-wget https://www.python.org/ftp/python/3.6.9/Python-3.6.9.tgz
-tar xzvf Python-3.6.9.tgz
-cd Python-3.6.9
-sudo ./configure --prefix=/opt/python3.6
-make -j $(nproc)
-sudo make install
-sudo ln -s /opt/python3.6/bin/python3.6 /usr/bin/python3.6
-```
-
-!!! warning
-
-    Python3.5 is preinstalled by default on Ubuntu 16.04, `python3 -V` gives `Python 3.5.2`, many system tools rely on it, please **DO NOT** bind python3 to any versions other than Python3.5, otherwise your system might have unexpected problems.
-
-!!! note
-
-    For a general Python installation not only for this Python3.6, if you have `gcc v8+`, you can add the flag `--enable-optimizations` to `./configure` to gain an extra runtime speed, otherwise you might encounter `Could not import runpy module` error
-
-### Using Python3.6 pip
-
-```bash
-python3.6 -m pip install [a python module]
-```
-
-### Prevent pip install without an active venv
-
-```bash
-echo 'export PIP_REQUIRE_VIRTUALENV=true' >> ~/.bashrc
-```
-
-## Installing Python3.7 on Ubuntu 16.04
-
-Just tested installing Python3.7.5 with the same procedure, all works.
-
 ## Installing Python3.10.10 with sqlite3 on Ubuntu 20.04 in WSL
 
+!!! note "Same procedure applied to other Python versions"
+
 ```bash
 # install build packages
 sudo apt update
+# without `libssl-dev` package, pip install will throw TLS/SSL error.
 sudo apt install -y build-essential zlib1g-dev libssl-dev libffi-dev
 
 # install sqlite3 from source, if you need a specific sqlite3 version in Python, you must install it before compiling Python, because the compilation needs the lib libsqlite3.so
@@ -113,14 +61,27 @@ wget https://www.python.org/ftp/python/3.10.10/Python-3.10.10.tgz
 tar xvf Python-3.10.10.tgz
 cd Python-3.10.10/
 
-# ubuntu 20.04 has gcc v9, so you can add the flag --enable-optimizations to ./configure
+# ubuntu 20.04 has gcc v9 (v8+ are OK), so you can add the flag --enable-optimizations to ./configure
+# to gain an extra runtime speed, otherwise you might encounter `Could not import runpy module` error
 # --with-bz2 is for pandas, otherwise modulenotfounderror: no module named '_bz2' pandas
-./configure --prefix=$HOME/opt/python3.10 --with-bz2
+version=$(basename "$(pwd)" | cut -d'-' -f2 | cut -d'.' -f1-2)
+sudo ./configure --prefix=$HOME/opt/python$version --with-bz2 --enable-optimizations
 make -j $(nproc)
 sudo make install
 make clean
-sudo ln -s ~/opt/python3.10/bin/python3.10 /usr/bin/python3.10
-ll $(which python3.10)
-echo -e '\nexport PIP_REQUIRE_VIRTUALENV=true' >> ~/.bashrc
-python3.10 -c 'import sqlite3 ; print(sqlite3.sqlite_version)'
+sudo ln -sf ~/opt/python$version/bin/python$version /usr/bin/python$version
+ll $(which python$version)
+if ! grep -q 'export PIP_REQUIRE_VIRTUALENV=true' ~/.bashrc; then
+    echo 'export PIP_REQUIRE_VIRTUALENV=true' >> ~/.bashrc
+    echo "added export PIP_REQUIRE_VIRTUALENV=true"
+fi
+python$version -c 'import sqlite3 ; print(sqlite3.sqlite_version)'
+```
+
+## Prevent pip install without an active venv
+
+```bash
+if ! grep -q 'export PIP_REQUIRE_VIRTUALENV=true' ~/.bashrc; then
+    echo 'export PIP_REQUIRE_VIRTUALENV=true' >> ~/.bashrc
+fi
 ```