Append your paths so there is only one PYTHONPATH.
PYTHONPATH="/Applications/python/common:/Applications/sitecustomize:$PYTHONPATH"
export PYTHONPATH
Then source ~/.bash_profile
OR import them into your Python script (this would only work for the script added to):
import sys
sys.path.append("/Applications/python/common")
sys.path.append("/Applications/sitecustomize")