brew install python3 didn't install pip3

Ok it took me a lot of googling but the problem is that in high sierra all permissions inside usr/local changed and homebrew has to create some folder inside usr/local. Here is how I solved everything:

I tried using sudo brew install python3 but that also threw an error directly from Homebrew telling me that it doesn't allow the use of sudo brew.

Create the folders I needed using sudo mkdir inside /usr/local:

sudo mkdir lib sudo mkdir Frameworks

Change the permissions inside /usr/local so that homebrew can access them:

sudo chown -R $(whoami) $(brew --prefix)/*

Now install python3

brew install python3

This will give you a successful installation:

==> Pouring python3-3.6.3.high_sierra.bottle.tar.gz==> /usr/local/Cellar/python3/3.6.3/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/Cellar/python3/3.6.3/bin --in==> /usr/local/Cellar/python3/3.6.3/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/Cellar/python3/3.6.3/bin --in==> /usr/local/Cellar/python3/3.6.3/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/Cellar/python3/3.6.3/bin --in==> CaveatsPip, setuptools, and wheel have been installed. To update them  pip3 install --upgrade pip setuptools wheelYou can install Python packages with  pip3 install <package>They will install into the site-package directory  /usr/local/lib/python3.6/site-packagesSee: https://docs.brew.sh/Homebrew-and-Python.html==> Summary🍺  /usr/local/Cellar/python3/3.6.3: 3,588 files, 56.1MB

After resolving the linking issue (e.g. https://github.com/Homebrew/homebrew-core/issues/19286 ), python3 is installed but not pip3. Reinstalling python (e.g. brew reinstall python) eventually installs pip3 as well. These steps works well for me.

GitHub user @aether2501, commenting on a sudo chown solution for a "Homebrew Permission Denied" problem, suggests instead that Homebrew be uninstalled/reinstalled after the upgrade to High Sierra.

I successfully used @aether2501's reinstall command, /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)", on High Sierra (10.13.2) without uninstalling brew first.

In addition to creating the /usr/local/Frameworks directory and setting the necessary ownership and permissions I needed to link python3, it also appears to have fixed other directory issues.