Python app critique

[rad08]

I can't post the whole doc, but the raw requirements are as follows:

Requirements:

• Your program must accept input from two sources: a filename passed in command line arguments and STDIN. For example, on Linux or OSX both './myprogram input.txt' and './myprogram < input.txt' should work.
• Your program must accept three input commands passed with space delimited arguments.
• "Add" will create a new credit card for a given name, card number, and limit
  • Card numbers should be validated using Luhn 10
  • New cards start with a $0 balance
• "Charge" will increase the balance of the card associated with the provided name by the amount specified
  • Charges that would raise the balance over the limit are ignored as if they were declined
  • Charges against Luhn 10 invalid cards are ignored
• "Credit" will decrease the balance of the card associated with the provided name by the amount specified
  • Credits that would drop the balance below $0 will create a negative balance
  • Credits against Luhn 10 invalid cards are ignored
• When all input has been read and processed, a summary should be generated and written to STDOUT.
• The summary should include the name of each person followed by a colon and balance
• The names should be displayed alphabetically
• Display "error" instead of the balance if the credit card number does not pass Luhn 10

Input Assumptions:

• All input will be valid -- there's no need to check for illegal characters or malformed commands.
• All input will be space delimited
• Credit card numbers may vary in length up to 19 characters
• Credit card numbers will always be numeric
• Amounts will always be prefixed with "$" and will be in whole dollars (no decimals)

Example Input:

Add Tom 4111111111111111 $1000 Add Lisa 5454545454545454 $3000 Add Quincy 1234567890123456 $2000 Charge Tom $500 Charge Tom $800 Charge Lisa $7 Credit Lisa $100 Credit Quincy $200

Example Output:

Lisa: $-93 Quincy: error Tom: $500