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  1. import re
  2.  
  3. s = 'K4[ON(SO3)2]2'
  4.  
  5. target = s.replace('[', '(').replace(']', ')')
  6. while True:
  7.     m = re.search(r'(\(([^()]*)\)(\d+))', target)
  8.     if not m:
  9.         break
  10.     substr, data, num = m.groups()
  11.     target = target.replace(substr, data * int(num))
  12.  
  13. result = {}
  14. for m in re.finditer(r'([A-Z][a-z]?)(\d+)?', target):
  15.     el, num = m.groups('1')
  16.     result[el] = result.get(el, 0) + int(num)
  17.  
  18. print(list(result.items()))
Success #stdin #stdout 0.03s 9636KB
comments (?)
stdin 
Standard input is empty
stdout 
[('K', 4), ('O', 14), ('N', 2), ('S', 4)]
https://ideone.com/n98WEs
language:
Python 3 (python  3.9.5)
created:
4 years ago
visibility:
secret

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