Single Player Blackjack

This program runs a simple player vs dealer blackjack game. The command to run the program is:
python Blackjack.py

The default starting balance for the player is $500. This can be specified with an additional argument.
For example, to specifiy a starting balance of $6000, one can run:
python Blackjack.py 6000

All code for this program can be found in Blackjack.py. The code uses the random and sys python libraries.

I'm not 100% clear on all the nitty gritty rules of Blackjack, but I think I got the gist of it. As requested, the dealer must hit on soft 17 and splitting is not allowed.
I tried to correctly implement push and double down. I assumed that a push is considered a tie and the player get's his/her money back.
I interpreted double down to mean that at any point in time, on his/her turn, the player can double down and double his/her bet, but will receive exactly one more card and then stand.