brew install on OSX has python issues

I have exactly same issue, but I use MacPort to install Byobu.

I've just discovered it this week, previously was using GNU Screen and start experimenting with tmux and hit Byobu. I use it on WSL, Ubuntu and my MacOS 10.13.6

It work the 1st time on my Mac, but since then I've also performed:
sudo port selfupdate
sudo port upgrade outdated

Then it still started, but once detached, I'm unable to invoke byobu again is it outputs the same error as above:
# delphym @ KiwiBook in /usr/bin [22:06:55]
$ byobu
/opt/local/bin/byobu-select-session: /opt/local/lib/byobu/include/select-session.py: /usr/bin/python3: bad interpreter: No such file or directory
/opt/local/bin/byobu-select-session: line 24: /opt/local/lib/byobu/include/select-session.py: Undefined error: 0

I also use ohmyz.sh as a shell.

Also as above, I've tried to fix it by creating a symlink, but I couldn't because of Apple's System Integrity Protection. (More info here: https://superuser.com/questions/933019/sudo-cant-create-file-in-usr-bin-in-el-capitan)

Location of python(s) in my system is:
$ ll /usr/bin/python*
-rwxr-xr-x 1 root wheel 65K 29 May 17:03 /usr/bin/python
-rwxr-xr-x 4 root wheel 925B 16 Jul 2017 /usr/bin/python-config
lrwxr-xr-x 1 root wheel 75B 21 Oct 2017 /usr/bin/python2.7 -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7
lrwxr-xr-x 1 root wheel 82B 21 Oct 2017 /usr/bin/python2.7-config -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7-config
-rwxr-xr-x 1 root wheel 65K 29 May 17:03 /usr/bin/pythonw
lrwxr-xr-x 1 root wheel 76B 21 Oct 2017 /usr/bin/pythonw2.7 -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/pythonw2.7

$ ll `which python3`
lrwxr-xr-x 1 root admin 24B 11 Sep 23:28 /opt/local/bin/python3 -> /opt/local/bin/python3.4

Looking into the src: https://github.com/dustinkirkland/byobu/blob/master/usr/lib/byobu/include/select-session.py
it's not much obvious to me (I'm very much Python beginner) where it's getting the /usr/bin PATH set.

Many thanks for looking into this issue soon.

Alright, it is not that black and white, so here're the reproduction steps:
Assumption: no byobu, tmux, nor screen processes are running
$ ps -ef |grep byobu
And if they do, kill them.

STEPS:
1. List all sessions:
$ byobu ls
no server running on /private/tmp/tmux-501/default

2. Start byobu. It surprisingly starts
$ byobu

3. List sessions again within the byobu session
$ byobu ls
1: 2 windows (created Sat Sep 29 23:00:15 2018) [153x20] (attached)

4. Detach from byobu (F6)
[detached (from session 1)]

5. List again its sessions
$ byobu ls
1: 2 windows (created Sat Sep 29 23:00:15 2018) [153x20]

6. Try to launch byobu again
$ byobu
/opt/local/bin/byobu-select-session: /opt/local/lib/byobu/include/select-session.py: /usr/bin/python3: bad interpreter: No such file or directory
/opt/local/bin/byobu-select-session: line 24: /opt/local/lib/byobu/include/select-session.py: Undefined error: 0

7. Check for its running processes
$ ps -ef | grep byobu
  501 49530 1 0 11:00pm ?? 0:02.41 tmux -u -2 -f /opt/local/share/byobu/profiles/tmuxrc new-session -n - /opt/local/bin/byobu-shell
  501 59119 44965 0 11:07pm ttys000 0:00.00 grep --color=auto --exclude-dir=.bzr --exclude-dir=CVS --exclude-dir=.git --exclude-dir=.hg --exclude-dir=.svn byobu

8. Kill the byobu process
$ kill -9 49530

# delphym @ KiwiBook in /usr/bin [23:07:55]
$ echo $?
0

9. Check the processes again:
$ ps -ef | grep byobu
  501 59173 44965 0 11:08pm ttys000 0:00.00 grep --color=auto --exclude-dir=.bzr --exclude-dir=CVS --exclude-dir=.git --exclude-dir=.hg --exclude-dir=.svn byobu

10. Repeat from step #1

To fix this, change the shebang line in
/usr/local/lib/byobu/include/select-session.py
(or /usr/local/Cellar/byobu/5.127/lib/byobu/include/select-session.py)

from:
#!/usr/bin/python3

to:
#!/usr/bin/env python3

This makes the code more portable -- and fixes this bug

Here is patched copy:
https://github.com/gerber/byobu/blob/gerber-patch-1/usr/lib/byobu/include/select-session.py

Hi @Ben, your fix works great! Thanks for it

Very sorry for late response, but being a dad of twins takes incredible amount of time and resources.

I've just tested on my:
 - Mac OS 10.13.6 with MacPort 2.5.4 and its Byobu port 5.127 (fixed problem)
 - Win 10 1803, with WSL Ubuntu 16.04.5 LTS, Byobu 5.106 (no regression, and here it doesn't matter if I refer to python 3 or just python).

Thanks again,
-d