from itertools import permutations
import re

def solve(problem):
    problem = re.sub('^([^=]+)=+(.*)$', r'(\1)-(\2)', problem)
    variables = compile(problem, '<string>', 'eval').co_names
    letters = [ord(x) for x in set(''.join(variables))]
    default_mapping = dict(zip(letters, [ord('5')] * len(letters)))
    max_depth = max(len(x) for x in variables)

    def reconstruct(expr):
        return re.sub(r'^\((.*?)\)-\((.*?)\)$', r'\1==\2', expr)

    def advance(n, mapping, remaining):
        def distance(candidate):
            newmap = mapping + candidate
            expr = problem.translate(dict(newmap)).translate(default_mapping)
            r = remaining
            if candidate:
                r = [d for d in remaining if all(d != c[1] for c in candidate)]
            return abs(eval(expr)), expr, newmap, r

        if n == max_depth:
            result = distance(())
            if not result[0]:
                yield reconstruct(result[1])
        else:
            nth = set(''.join(v[n:n+1] for v in variables))
            letters = [ord(x) for x in nth if ord(x) not in dict(mapping)]
            if not letters:
                yield from advance(n + 1, mapping, remaining)
            else:
                xs = [ord(x) for x in '123456789'] if n == 0 else remaining
                ps = permutations(xs, len(letters))
                for r in sorted(distance(tuple(zip(letters, c))) for c in ps):
                    yield from advance(n + 1, r[2], r[3])

    yield from advance(0, (), [ord(x) for x in '0123456789']) 

print(next(solve('send + more = money')))
print(next(solve('apple + grape = cherry')))

  Line 31
    yield from advance(n + 1, mapping, remaining)
             ^
SyntaxError: invalid syntax