D&D_Dice_Roller.py

#! /usr/bin/python2.7

from random import seed, randint
from re import findall, match

def parse_input(_input):
    _input = _input.lower()
    # quit if requested
    if findall('exit|quit', _input.lower()):
        import sys
        sys.exit()
    # Check for validity: 
    #   1. If one integer X is given, assume 1dX (e.g. 100).
    #   2. Only integers and "d"
    #   3. Can not roll a die with zero sides
    #   4, Only one "d" allowed
    check = match('[0-9]+[d][1-9]+[0-9]*', _input)
    # Validity checks 2-4
    if check and check.group() == _input:
        nums = [int(num) for num in _input.split('d')]
    # Validity Check 1
    elif not findall('[^0-9]', _input):
        nums = [1, int(_input)]
    else:
        return
    return int(nums[0]), int(nums[1])

def roll_die(number_of_sides):
    seed()
    return randint(1, number_of_sides)

def roll_dice(num_of_dice, num_of_sides):
    return [ str(roll_die(num_of_sides)) for dice in range(num_of_dice) ]

def prompt_user(prompt_string=None):
    if prompt_string: 
        print prompt_string
    return raw_input(">> ")

def print_roll(_input, roll):
    print "---"*3
    print "Rolling %s" % _input
    print ", ".join(roll)

def welcome_message(name):
    print "-"*40
    print "-"*40
    print "> Time to roll some dice, %s." % name
    print "> Enter a roll."
    print "> e.g. 2d6, 1d20, 3d12, etc."
    print "> Tip: Entering a single number (e.g. 100) will roll 1 die that size"
    print "> Type 'exit' or 'quit' to quit."
    print "-"*40
    print "-"*40

def main():
    name = raw_input("What is your name?\n> ")
    welcome_message(name if name else 'nerd')
    prompt_string = None
    while True:
        try:
            _in = prompt_user(prompt_string)
            roll_input = parse_input(_in)
            if roll_input:
                roll = roll_dice(*roll_input)
                print_roll(_in, roll)
                prompt_string = None
            else:
                prompt_string = "Invalid roll. Try again."
        except KeyboardInterrupt:
            print "\n> Type 'exit' or 'quit' to quit."

if __name__=='__main__':
    main()