finite-state-machine

syn match pythonEscape +{{+ contained containedin=pythonfString,pythonfDocstring
syn match pythonEscape +}}+ contained containedin=pythonfString,pythonfDocstring

syn region pythonfString matchgroup=pythonQuotes
      \ start=+[fF]\@1<=\z(['"]\)+ end="\z1"
      \ contains=@Spell,pythonEscape,pythonInterpolation
syn region pythonfDocstring matchgroup=pythonQuotes
      \ start=+[fF]\@1<=\z('''\|"""\)+ end="\z1" keepend
      \ contains=@Spell,pythonEscape,pythonSpaceError,pythonInterpolation,pythonDoctest