criptarithmetic.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Tue Feb  5 15:31:57 2019

@author: irina
"""
from __future__ import division
import string, re, itertools

def solve(formula):
    """Given a formula like 'ODD + ODD == EVEN', fill in digits to solve it.
    Input formula is a string; output is a digit-filled-in string or None."""
    for f in fill_in(formula):
        if valid(f):
            return f
    
def fill_in(formula):
    "Generate all possible fillings-in of letters in formula with digits."
    letters = "".join(set(re.findall('[A-Z]', formula)))
    for digits in itertools.permutations('1234567890', len(letters)):
        table = string.maketrans(letters, ''.join(digits))
        yield formula.translate(table)
    
def valid(f):
    """Formula f is valid if and only if it has no 
    numbers with leading zero, and evals true."""
    try: 
        return not re.search(r'\b0[0-9]', f) and eval(f) is True
    except ArithmeticError:
        return False


def faster_solve(formula):
    """
    Give

def compile_word(word):
    """Compile a word of uppercase letters as numeric digits.
    E.g., compile_word('YOU') => '(1*U+10*O+100*Y)'
    Non-uppercase words unchanged: compile_word('+') => '+'"""
    if word.isupper():
        terms = [('%s*%s' % (10**i, d)) for (i,d) in enumerate(word[::-1])]
        return '(' + '+'.join(terms) +')'
    else:
        return word