ensure and add comments to base python formulas

builds/runtimes/python3

@@ -9,12 +9,11 @@ OUT_PREFIX=$1
 BIN_DIR="$(cd "$(dirname "$0")"/../.. || exit; pwd)/bin"
 export BIN_DIR
 
+# Orient ourselves and build download link
 dep_formula=${0#$WORKSPACE_DIR/} # this is the original script, e.g. pypy-5.3.1
-dep_name=$(basename $BASH_SOURCE) # this is us
-
-BASE=${dep_formula##*/}
-python_version=${BASE^}
-version_number=$(echo "$python_version" | cut -d- -f2)
+BASE=${dep_formula##*/} # this gives us relative path
+python_version=${BASE^} # this gives us only the filename with version number
+version_number=$(echo "$python_version" | cut -d- -f2) # this returns just X.X.X
 dep_url=https://python.org/ftp/python/${version_number}/${python_version}.tgz
 
 # shellcheck source=bin/utils