I've downloaded the Selenium zip file for python and it contains the folder with the setup.py. It says on python.org that I have to type in terminal 'python setup.py install' but it gives me this error that I need to be administrator because I have no permission to the directory, when in fact my user is already an administrator:

Checking .pth file support in /Library/Python/2.7/site-packages/
error: can't create or remove files in install directoryThe following error occurred while trying to add or remove files in the
installation directory:[Errno 13] Permission denied: /Library/Python/2.7/site-packages/test-easy-install-1469.pth'The installation directory you specified (via --install-dir, --prefix, or
the distutils default setting) was:/Library/Python/2.7/site-packages/Perhaps your account does not have write access to this directory?  If the
installation directory is a system-owned directory, you may need to sign in
as the administrator or "root" account.  If you do not have administrative
access to this machine, you may wish to choose a different installation
directory, preferably one that is listed in your PYTHONPATH environment
variable.For information on other options, you may wish to consult the
documentation at:https://pythonhosted.org/setuptools/easy_install.htmlPlease make the appropriate changes for your system and try again.`

I prefer not to touch Mac's default python. Instead I would suggest to brew your own python

Install brew from https://brew.sh/

then install python

brew install python3

Then install selenium

pip3 install selenium