splitting using regex python for complicated strings [duplicate]

Question

I want to splitting a string such as Si(C3(COOH)2)4(H2O)7 into the following

[Si, (C3(COOH)2), 4, (H2O), 7]

That is, entire paranthesis expressions turn into an element by themselves. I've tried a number of different combinations with re.findall() to no avail. Any help is greatly appreciated.

You can't parse nested structures with regular expressions in Python, so there's no way to find out which ( or ) to split on. — Zero Piraeus
– Zero Piraeus, Commented Nov 11, 2016 at 18:44

Terry Jan Reedy · Accepted Answer · 2016-11-11 22:47:05Z

0

You have to scan the string yourself, keeping track of the nesting depth. The significant 'events' are 'at beginning of string', 'at (', 'at )', and 'at end of string'. At each event, consider depth and reset it.

inn = 'Si(C3(COOH)2)4(H2O)7'
out = ['Si', '(C3(COOH)2)', '4', '(H2O)', '7']
res = []
beg = 0
dep = 0
for i, c in enumerate(inn):
    if c == '(':
        if dep == 0 and beg < i:
            res.append(inn[beg:i])
            beg = i
        dep += 1
    elif c == ')':
        if dep == 0:
            raise ValueError("')' without prior '('")
        elif dep == 1:
            res.append(inn[beg:i+1])
            beg = i+1
        dep -= 1
if dep == 0:
    res.append(inn[beg:i+1])
else:
    raise ValueError("'(' without following ')'")
print(res, res == out)

# prints
# ['Si', '(C3(COOH)2)', '4', '(H2O)', '7'] True

edited Nov 11, 2016 at 22:47

answered Nov 11, 2016 at 22:39

Terry Jan Reedy

19.3k3 gold badges44 silver badges57 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

splitting using regex python for complicated strings [duplicate]

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related