Python: backquote in strings try to execute `sdist` command

A cut & past from markdown result in the following, non blocking issue:

$ echo -e "\e[0Ksection_start:`date +%s`:python-build\r\e[0KBuild distribution `sdist` and `wheel` from '${PYTHON_SOURCE_DIR}'"
/bin/bash: line 135: sdist: command not found
Build distribution  and usage: wheel [-h] {unpack,pack,convert,version,help} ...
positional arguments:
  {unpack,pack,convert,version,help}
                        commands
    unpack              Unpack wheel
    pack                Repack wheel
    convert             Convert egg or wininst to wheel
    version             Print version and exit
    help                Show this help
options:
  -h, --help            show this help message and exit from '.'