ln -sf /usr/local/bin/python3 /usr/local/bin/python
type -a python
# Result:
# python is /usr/bin/python
# python is /usr/local/bin/python
## type on terminal
which python3
PATH="/Library/Frameworks/Python.framework/Versions/3.1/bin:${PATH}"
export PATH
PYTHONPATH="/Me/Documents/mydir:$PYTHONPATH"
export PYTHONPATH