Formatting string by braces with braces escaping

Question

I have a string, that contains expresions in braces:

string = "3+3={3+3}"

I want to find all expresions and replace them by result of expression (using eval). Also I want to make some kind of braces escaping mechanism. I can do it by myself:

final = ""
opened_eval = False
short_escaping = False
long_escaping = False
inner_string = ""
for letter in string:
    if opened_eval:
        if letter == "}":
            final += eval(inner_string, kwargs)
            inner_string = ""
            opened_eval = False
        else:
            inner_string+=letter
    elif short_escaping:
        opened+=letter
        short_escaping=False
    elif long_escaping:
        if letter == "|":
            long_escaping=False
        else:
            opened+=letter
    else:
        if letter == "\\":
            short_escaping=True
        elif letter == "|":
            long_escaping=True
        elif letter=="{":
            opened_eval = True
        else:
            final+=letter

>>> print(final)
3+3=6

But I care about, how quickly does it work, so I want to use C function. I tryed to do that with re.finditer (r"\{\w+\}"), but I don't know, how can I make escaping with re. So I need something like this:

for expression in find(r"a = {get_a()} \{text in braces\} b = {get_b()}"):
    print(expression.text, expression.start, expression.end)

{get_a()} 5 13
{get_b()} 38 46

Answer 1

Faster way to do this:

After import re, define a string:

string = "3+3={3+3}, 7:4={7/4}, etc.."

find all the arguments in the brackets:

equations = re.findall("\{[^\{\}]*\}", string)
>>>['{3+3}', '{7/4}']

solve the equations:

results = [list(eval(equation))[0] for equation in equations]
>>>[6, 1.75]

finally replace the brackets in the string (sub) and format the string with the results:

re.sub("\{[^\{\}]*\}","{}",string).format(*results)
>>>'3+3=6, 7:4=1.75, etc..'