Enigma.py

from re import match
letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890 ,.?!:$()"
print("Installing data... Please wait...")
exec("primes = [2,"+open("PrimesDataBase.pr", "r").read()+"]")
print("Data installed")
def get_beginning():
    try:
        return int(input("Enter the first number to use:\n"))
    except:
        print("Must be a number")
        get_beginning()
beginning = int(get_beginning())
print(25*"="+"Important!"+25*"="+"\n"+6*"="+"After "+str(len(primes))+" characters it will be the same key"+7*"=")
while 0 == 0:
    dat = ""
    EnOrDeCode = input("Encode or Decode?\n")
    if match(r"^( +)?[eE][nN]([cC]([oO]([dD]([eE])?)?)?)?( +)?$", EnOrDeCode):
        En = input("Enter text to Encode:\n")
        for i in range(len(En)-1, -1, -1):
            try:
                if i+beginning < len(primes):
                    ip = i+beginning
                else:
                    ip = (i+beginning) %len(primes)
                if letters.index(En[i])+primes[ip] <= len(letters)-1:
                    ind = letters.index(En[i])+primes[ip]
                else:
                    ind = (letters.index(En[i])+primes[ip]) % len(letters)
                dat += letters[ind]
            except ValueError:
                dat += "-"
        print(dat)
    elif match(r"^( +)?[dD][eE]([cC]([oO]([dD]([eE])?)?)?)?( +)?$", EnOrDeCode):
        datOne = ""
        DeOne = input("Enter text to Decode:\n")
        De = ""
        for i in range(len(DeOne)-1, -1, -1):
            De += DeOne[i]
        for i in range(len(De)-1, -1, -1):
            if De[i] != "-":
                if i+beginning < len(primes):
                    ip = i+beginning
                else:
                    ip = (i+beginning) %len(primes)
                if letters.index(De[i])-primes[ip]<0:
                    ind = (letters.index(De[i])-primes[ip]) % len(letters)
                else:
                    ind = letters.index(De[i])-primes[ip]
                    datOne += letters[ind]
            else:
                datOne += "-"
        for i in range(len(datOne)-1,-1,-1):
            dat += datOne[i]
        print(dat)
    else:
        print("try again")