I suspect the scope of this UX "bug" is larger than python.  I think this probably affects every executable written in an interpreted
language and using a shebang.  Here's another example with a bash
script:

  $ cat > t.sh
  #!/bin/bash
  sed 's/\x0/\\0/g'  # replaces null bytes with a visible '\0'
  
  $ ./t.sh </proc/self/cmdline
  /bin/bash\0./t.sh\0

Looks like '/bin/bash' is argv[0].  What happens when we try exec -a:
  
  $ bash -c 'exec -a FOO bash t.sh </proc/self/cmdline'
  FOO\0t.sh\0

  $ bash -c 'exec -a FOO ./t.sh </proc/self/cmdline'
  /bin/bash\0/tmp/t.sh\0

"t.sh" still appears. The result of that last command surprised me,
there's no FOO in /prod/self/cmdline at all (still confused)!  By the
way, bash does the same as python, in that $0 always references the
script name, never the actual argv[0]:

  $ cat >s.sh
  #!/bin/bash
  echo $0
  
  $ ./s.sh </proc/self/cmdline
  ./s.sh

  $ bash s.sh </proc/self/cmdline
  s.sh

I'm not sure what the solution is.

Troy