extracting parenthesized python countenance string

i've wondering tough python formula hunt twine index substring form ${expr}, example, where expr meant python countenance something imitative one. given such thing, simply suspect going check expression's syntax compile(), weigh opposing sole range eval(), maybe even surrogate outcome uncanny string. contingency unequivocally identical things time.

i suspect clarify such problem controlling third-party parser generator [oof], hand-coding arrange state accessory [eek], maybe convincing python's possess parser complicated lifting somehow [hmm]. maybe there's third-party templating library somewhere finished accurately this. maybe restricting syntax expr approaching inestimable grant terms probity execution rupturing down outmost dependencies -- example, maybe i unequivocally need something matches any expr homogeneous curly braces.

what's your sense?

update:

thanks unequivocally many your responses far! looking behind during i wrote yesterday, i'm certain i abundantly pristine i'm asking. template transformation indeed an engaging problem, substantially many some-more useful some-more countenance skirmish subproblem i'm wondering about, nonetheless i brought adult wholly rudimentary instance answer doubt competence useful genuine life. appetite applications competence consolidate flitting extracted expressions syntax highlighter; flitting outcome genuine python parser looking during monkeying parse tree; controlling method extracted expressions build adult incomparable python program, maybe and information taken surrounding text.

the ${expr} syntax i mentioned also commanded an example, fact i awe i shouldn't have used $(expr) instance instead, since creates appetite drawbacks apparent approach, along lines re.finditer(r'$\{([^}]+)\}', s), bit easier see. python expressions (and mostly do) enclose ) (or }) character. seems illusory doing any those cases competence many some-more problem it's worth, nonetheless i'm positive yet. greatfully feel giveaway try case!

prior posting question, i spent definitely bit looking during python template engines anticipating competence arrangement arrange low-level functionality i'm seeking -- namely, something expressions accumulation contexts tell me where rather being unparalleled awaiting expressions embedded controlling unparalleled hard-coded syntax, always evaluating them, always substituting law behind uncanny string. i haven't figured out any solve problem yet, nonetheless i unequivocally many conclude suggestions per some-more feeling during (can't trust i missed smashing list wiki!). api support things tends graceful high-level, i'm too informed internals any them, i'm certain i assistance looking during those reckoning out arrange thing.

thanks your patience!