Задача: перебор всех вариантов/ парсинг

from itertools import cycle, product
 
 
def fin_ned(buf, need):  # search of second needed symbol
    coun = 0
    for item in range(len(buf)):
        if buf[item] == need:
            coun += 1
            if coun == 2:
                return item
    return False
 
 
def get_next(mass):  # next_option
    for i in mass:
        yield i
 
 
def full_mass_of_options(array_of_options, count_of_options):  # creating an array of all options
    new_arr = []
    for item in array_of_options:
        cyc = cycle(item)
        new_arr.append([next(cyc) for i in range(count_of_options)])
    return new_arr
 
 
st = "{A|B} {B|C|D} {{E|F} G|H}."
 
array_of_options = []
arr = []
count_of_options = 1
number_of_substitutions = 0
 
# text splitting, search options
while "{" in st:
    if "{" in st[st.index('{') + 1:st.index('}')]:  # seach of nested structure
        array_of_options.append([submass for submass in st[fin_ned(st, '{') + 1:st.index('}')].split('|')])
        st = st[0:fin_ned(st, '{')] + str(number_of_substitutions) + st[st.index('}') + 1:len(st)]
        number_of_substitutions += 1
    else:
        array_of_options.append([submass for submass in st[st.index('{') + 1:st.index('}')].split('|')])
        st = st[0:st.index('{')] + str(number_of_substitutions) + st[st.index('}') + 1:len(st)]
        number_of_substitutions += 1
number_of_substitutions -= 1
 
# preparation of initial arrays
for item in array_of_options:
    count_of_options *= len(item)
array_of_options = full_mass_of_options(array_of_options, count_of_options)
full_sample = [st for item in range(count_of_options)]
 
# assembly of an array of variants
for itr in range(number_of_substitutions, -1, -1):
    gen = get_next(array_of_options[itr])
    for itm in range(count_of_options):
        if str(itr) in full_sample[itm]:
            full_sample[itm] = full_sample[itm].replace(str(itr), next(gen))
 
# final
for i in enumerate(set(full_sample)):
    print(*i)