The issue of converting && in Bash to Python has been resolved with the assistance of Xymostech, whose help is greatly appreciated -- thank you!
The command line at issue (from the Bash terminal) is: latexmk file.tex && latexmk -c file.tex.
Here is the plugin if anyone is interested:
https://github.com/lawlist/ST2-plugin-latexmk-save-build-clean