I made a simple blackjack game in Python 3.4.3. I'm a beginner, so it would be awesome if you could rip up my code and tell me everything I did wrong. I know there's no insurance for when the dealer has an ace (yet), and there's some other blackjack rules that I'm going to add in the future, but I wanted to get a base code out there. Thanks!

import random as r
import itertools as i


suit = 'scdh'
rank = '23456789TJQKA'
deck = tuple(''.join(card) for card in i.product(rank, suit))
val = ()
for _ in range(9):
    val = val + (_+2, _+2, _+2, _+2)
    if _ == 8:
        for __ in range(3):
            val = val + (10, 10, 10, 10)
val = val + (1, 1, 1, 1)
deckval = dict(zip(deck, val))


def deal():
    global hand, dealer_hand, player_hand, counter
    hand = r.sample(deck, 52)
    counter = 0
    dealer_hand = list(hand[counter:counter + 1])
    counter += 2
    player_hand = list(hand[counter:counter + 2])
    counter += 2


def sum_player_hand():
    global hand, player_hand, counter, player_sum, opt_player_sum
    player_sum = 0
    opt_player_sum = 0
    for a in range(len(player_hand)):
        if int(deckval[player_hand[a]]) == 1 and opt_player_sum + int(deckval[player_hand[a]]) <= 21:
            opt_player_sum = player_sum + int(deckval[player_hand[a]]) + 10
            player_sum += int(deckval[player_hand[a]])
        elif opt_player_sum > 21:
            player_sum += int(deckval[player_hand[a]])
            opt_player_sum = player_sum
        else:
            player_sum += int(deckval[player_hand[a]])
            opt_player_sum += int(deckval[player_hand[a]])


def dealer_init():
    global hand, dealer_hand, counter, dealer_sum, opt_dealer_sum
    dealer_sum = 0
    opt_dealer_sum = 0
    if int(deckval[dealer_hand[0]]) == 1:
        dealer_sum += int(deckval[dealer_hand[0]])
        opt_dealer_sum += dealer_sum + 10
    else:
        dealer_sum = int(deckval[dealer_hand[0]])
        opt_dealer_sum = int(deckval[dealer_hand[0]])
    dealer_logic()


def dealer_logic():
    global hand, dealer_hand, counter, dealer_sum, opt_dealer_sum
    if dealer_sum >= 17 or opt_dealer_sum >= 17:
        pass
    else:
        while opt_dealer_sum <= 16:
            dealer_sum = 0
            opt_dealer_sum = 0
            dealer_hand = dealer_hand + list(hand[counter:counter + 1])
            counter += 1
            for _ in range(len(dealer_hand)):
                if int(deckval[dealer_hand[_]]) == 1 and (opt_dealer_sum + int(deckval[dealer_hand[_]])) <= 21:
                    opt_dealer_sum += int(deckval[dealer_hand[_]])
                    dealer_sum += int(deckval[dealer_hand[_]])
                else:
                    dealer_sum += int(deckval[dealer_hand[_]])
                    opt_dealer_sum += int(deckval[dealer_hand[_]])


def main():
    global hand, dealer_hand, player_hand, counter, player_sum,     dealer_sum, opt_player_sum, opt_dealer_sum
    sum_player_hand()
    print('\nDealer has:', dealer_hand[0:2], '--')
    if player_sum <= 21:
        if opt_player_sum == player_sum or opt_player_sum > 21:
            print('Your hand is:', player_hand, '\n', 'Your sum is:', player_sum)
        else:
            print('Your hand is:', player_hand, '\n', 'Your sum is:', player_sum, 'or', opt_player_sum)
        choice = input('Hit or stay? ').lower()
        if choice == 'hit':
            player_hand = player_hand + list(hand[counter:counter + 1])
            counter += 1
            main()
        elif choice == 'stay':
            print('')
            if opt_player_sum <= 21:
                print('Final Hand: ', player_hand, 'Final Sum:', opt_player_sum)
                dealer_init()
                if opt_dealer_sum <= 21:
                    print('Dealer has:', dealer_hand, 'Sum:', opt_dealer_sum)
                    if 21 >= opt_dealer_sum > opt_player_sum:
                        print('DEALER WINS')
                    else:
                        print('YOU WIN')
                    run()
                else:
                    print('Dealer has:', dealer_hand, 'Sum:', dealer_sum)
                    if 21 >= dealer_sum > opt_player_sum:
                        print('DEALER WINS')
                    else:
                        print('YOU WIN')
                    run()
            else:
                print('Final Hand: ', player_hand, '\n', 'Final Sum:', player_sum)
                dealer_init()
                if opt_dealer_sum <= 21:
                        print('Dealer has:', dealer_hand, 'Sum:', opt_dealer_sum)
                    if 21 >= opt_dealer_sum > player_sum:
                        print('DEALER WINS')
                    else:
                        print('YOU WIN')
                    run()
                else:
                    print('Dealer has:', dealer_hand, 'Sum:', dealer_sum)
                    if 21 >= dealer_sum > player_sum:
                        print('DEALER WINS')
                    else:
                        print('YOU WIN')
                    run()
            else:
                print('')
                print('***Please enter hit or stay***')
                main()
        else:
            print('BUST\nYOUR HAND WAS:', player_hand, '\nYOUR SUM WAS:', player_sum, '\n')
        dealer_init()
        if opt_dealer_sum < 21:
            print('Dealer has:', dealer_hand, 'Sum:', opt_dealer_sum)
            if dealer_sum > 21:
                print('DEALER BUSTS')
            run()
        else:
            print('Dealer has:', dealer_hand, 'Sum:', dealer_sum)
            if dealer_sum > 21:
                print('DEALER BUSTS')
            run()


def run():
    play = input('********************\nWould you like to play again?').lower()
    if play == 'yes':
        deal()
        main()
    elif play == 'no':
        pass
    else:
        print('Please enter yes or no')
        run()


deal()
main()
run()