Path variables become longer and longer after doing source ~/.bashrc - bash

Question

This might be a stupid question, but I wonder how to avoid this problem.
In my ~/.bashrc file, I add some local paths. The following is an example of the PYTHONPATH. In my work environment, I need to do "source ~/.bashrc" from time to time, and the following PYTHONPATH becomes longer and longer which is quite annoying.
Instead of appending to the existing PYTHONPATH, it might be nicer if I can append it to the "clean" PYTHONPATH. Is there anyway of doing this?
export PYTHONPATH=$PYTHONPATH:$CLIENTS:$EXPERIMENTAL/my_pythonlib:/mnt/src/cloud/chanwcom/chanwcom-speech/mnt/experimental/users/chanwcom/bin:$CK_MEDIA_FRAMEWORK

Answer 1

EDIT: I answered the question about keeping a clean PATH.
#mklement0 commented correctly, that the OP is talking about the PYTHONPATH.
I could correct my answer, but perhaps other readers have the same problem for PATH.
Dear Chanwcom, you can use the methods beneath, you only need to rename the variables.
Add some tests before expanding your path. Choose one of these examples.
if [[ -z "${my_clean_path}" ]]; then
my_clean_path="${PATH}"
fi
# some more commands
PATH="${my_clean_path}:${PYTHONPATH}"
or
if [[ -z "${python_added}" ]]; then
PATH="${PATH}:${PYTHONPATH}" # PATH += also possible here
fi
or (my favorite, without additional variables)
if [[ "${PATH}" != *${PYTHONPATH}* ]]; then
PATH="${PATH}:${PYTHONPATH}" # PATH += also possible here
fi
or open a second shell before changing the path. exit to the first shell and open a new fresh shell.

Answer 2

The "right" way to solve this is as chepner mentioned in a comment -- modify your PYTHONPATH in .bash_profile which gets run at login, rather than in .bashrc which gets run for every shell.
If you're unable to adjust the scripts or tools that append repeated items to your path, you may be able to clean things up by removing non-unique values.
Here's a strategy I use, which involves converting my $PATH to an array, inverting the array (i.e. turning array values into subscripts of an associative array) and then rebuilding the path from the array index:
if [[ ${BASH_VERSINFO[0]} -ge 4 ]]; then
path_a=( ${PATH//:/ } )
declare -A path_b=()
for i in ${path_a[#]}; do path_b[$i]=1; done
IFS=: eval 'PATH="${!path_b[*]}"'
fi
export PATH
You can adjust this for PYTHONPATH easily enough.
Note that associative arrays were introduced with Bash version 4, so they may not be available with the default bash in OSX. You should be fine just about anywhere else that's modern, though.
Note also that this solution will break if any of the directories in the path contain colons. But your path would be broken in that case anyway, I think.
Also, note that this solution uses eval, which some people consider dangerous, unclean, smelly. In the right setting, though, it can be a fine cheese.