Relations between python 2.7 3 3.7, scipy, pip?

[Gribouillis]

You should be able do install pip through the command

Output:
python3.7 -m ensurepip --upgrade

as indicated in python's documentation.
Then you should be able to install scipy etc with the command

Output:
python3.7 -m pip install --user numpy scipy matplotlib ipython jupyter pandas sympy nose

as suggested in scipy documentation.

Do I need to install scipy, numpy for each version of python?

Yes, every module needs to be installed for each version of python (not only scipy and numpy).