python activate virtual environment

I haven't used the python virtual environment for a long time. If I want to activate the virtual environment built before, I use source activate to activate it directly. I find that it always goes to the root directory. After tossing for half an hour, I found that I need to add a file name behind it.
Join directly using source activeate, (root) zzz@zzz-System-Product-Name, will enter this directory.
If the file name source activate py3 is added later, it will enter (py3) zzz@zzz-System-Product-Name.
Record it here.