[GCC 4.2.1 (Apple Inc. build 5646)] is the version of GCC that the Python(s) were built with, not the version of Python itself. That information should be on the previous line. For example:

# Apple-supplied Python 2.6 in OS X 10.6
$ /usr/bin/python
Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49) 
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 

# python.org Python 2.7.2 (also built with newer gcc)
$ /usr/local/bin/python
Python 2.7.2 (v2.7.2:8527427914a2, Jun 11 2011, 15:22:34) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

Items in /usr/bin should always be or link to files supplied by Apple in OS X, unless someone has been ill-advisedly changing things there. To see exactly where the /usr/local/bin/python is linked to:

$ ls -l /usr/local/bin/python
lrwxr-xr-x  1 root  wheel  68 Jul  5 10:05 /usr/local/bin/python@ -> ../../../Library/Frameworks/Python.framework/Versions/2.7/bin/python

In this case, that is typical for a python.org installed Python instance or it could be one built from source.

In unix (mac os X included) terminal you can do

which python

and it will tell you.

You could have multiple Python versions on your macOS.

You may check that by command, type or which command, like:

which -a python python2 python2.7 python3 python3.6

Or type python in Terminal and hit Tab few times for auto completion, which is equivalent to:

compgen -c python

By default python/pip commands points to the first binary found in PATH environment variable depending what's actually installed. So before installing Python packages with Homebrew, the default Python is installed in /usr/bin which is shipped with your macOS (e.g. Python 2.7.10 on High Sierra). Any versions found in /usr/local (such as /usr/local/bin) are provided by external packages.

It is generally advised, that when working with multiple versions, for Python 2 you may use python2/pip2 command, respectively for Python 3 you can use python3/pip3, but it depends on your configuration which commands are available.

It is also worth to mention, that since release of Homebrew 1.5.0+ (on 19 January 2018), the python formula has been upgraded to Python 3.x and a python@2 formula will be added for installing Python 2.7. Before, python formula was pointing to Python 2.

For instance, if you've installed different version via Homebrew, try the following command:

brew list python python3

or:

brew list | grep ^python

it'll show you all Python files installed with the package.

Alternatively you may use apropos or locate python command to locate more Python related files.

To check any environment variables related to Python, run:

env | grep ^PYTHON

To address your issues:

• Error: No such keg: /usr/local/Cellar/python

  Means you don't have Python installed via Homebrew. However double check by specifying only one package at a time (like brew list python python2 python3).

• The locate database (/var/db/locate.database) does not exist.

  Follow the advice and run:

  sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.locate.plist
  

  After the database is rebuild, you can use locate command.