How can I edit PYTHONPATH on a Mac?

How can I permanently change the PYTHONPATH on a mac? I've tried editing .bash_profile, but when I use print sys.path in a file it gives a huge list of different URLs than the .bash_profile. In Terminal when I type echo $PYTHONPATH it shows a blank line. I don't want to use sys.path.append('...') because then I have to put that in every file.

How do you permanently change PATH variable on Mac?

Setting the PATH Variable Permanently To do this, you need to access the shell's configuration or profile file and add the program's path to it. Depending on the macOS version you're running on your Mac, this can be done via either the bash shell or zsh (z shell).

You can append the path to $PATH and not to $PYTHONPATH.
if you insist to change the PYTHONPATH, in some context that is prefferable:

do this:
```
export PYTHONPATH=$PYTHONPATH:/Users/username/pymodules
```
To make sure you are following the convention of what to append to PYTHONPATH see What exactly should be set in PYTHONPATH?.