"find . -name '* .py' -exec grep 'import' {} +" will work more like the xargs example, i.e. all filenames will be passed as parameters to a single grep process,

"find . -name '* .py' -exec grep 'import' {} +" will work more like the xargs example, i.e. all filenames will be passed as parameters to a single grep process, so the filename is displayed by default. I usually don't bother with this kind of command line micro-optimization, but in my experience find and grep are the commands for which it's worth knowing and using every option.