Get stderr after redirecting output to dialog gauge

I am using a python file to scrape a link, but to do that it takes some time, it prints 33, 66 and 100 normally and print the link to stderr using sys.write.stderr(var) Now, I want to run this command python file.py | dialog --gauge "Doing stuffs" 10 35 0 and want to pipe the stdout(33, 66, 100 for updating percentage) to gauge and get the sterr to a variable. { python3 file.py 2>&3 | dialog --gauge "Doing stuffs" 10 35 0; } 3>&1 this command runs dialog correctly and then print the stderr, but I can't take its output unless It is made to run in subshell. But doing so will make the dialog disappear.