python subdirectories

[snippsat]

dist-packages is a Debian-specific convention that is also present in its derivatives, like Ubuntu.
Debian Python Wiki:

dist-packages instead of site-packages.
Third party Python software installed from Debian packages goes into dist-packages, not site-packages.
This is to reduce conflict between the system Python, and any from-source Python build you might install manually.

Means that if you manually install Python from source,it uses the site-packages directory.
site-packages or dist-packages is the place Python install 3-party modules/package.

Testing on Mint 19.
I use pyenv it will use site-packages folder.

pip -V
pip 19.0.3 from /home/tom/.pyenv/versions/3.7.3/lib/python3.7/site-packages/pip (python 3.7)

# Going back to original Python version(3.6.5) on Mint 19
$ pyenv local system
$ pip -V
pip 18.0 from /home/tom/.local/lib/python3.6/site-packages/pip (python 3.6)

So Mint 19 use site-packages.

Test Ubuntu 14 i run on Cloud9,here use dist-packages.

snippsat:~/workspace/bs4_test $ pip -V
pip 9.0.1 from /usr/local/lib/python3.5/dist-packages (python 3.5)

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As note so has Windows always used site-packages,as folder for 3-party installed modules/package.