Python - checking raw_input string for two simultaneous conditions?

Question

Apologies for basic nature of this query - this is almost my first Python script.

I want the user to enter a two character string corresponding to a playing card (eg 2c, 3s) and for the program to check two things: first, whether it's in the list of valid cards, and second, whether that card has already been entered. If either condition is failed, I want the user to be prompted to re-enter the card. What I have written does each of those things, but it doesn't do them simultaneously - eg, if the card is invalid, the user is prompted, but if the re-entered card is already on the list, no prompt occurs. I can't see how to get both things tested at once.

Anyway, here is what I have:

posscards=["ac",
           "2c",
           "3c",
           "4c",
           "5c" #and so on] 


for x in range(0, decksize):
        answer=raw_input("next card? ")
        while answer not in posscards:
            answer = raw_input("not a possible card - try again: ")
        while answer in deck1:
            answer = raw_input ("you've already had that one - try again: ")
        deck1.append(answer)

As a side note, you might want to write some code to generate the postcards list instead of writing it out manually. Then you only need to write 13+4 values instead of 13*4, and you can write those 13 values as just a 13-character string. For example, posscards = [value+suit for suit in 'cshd' for value in 'a23456789tjqk'] Even if you don't understand that nested list comprehension (which you probably don't), you should be able to write it as a 4-line for statement. — abarnert
– abarnert, Commented Nov 14, 2013 at 22:40

abarnert · Accepted Answer · 2013-11-14 22:34:27Z

Instead of two while loops, you can use a single while loop with two if conditions. For example:

prompt = "next card? "
while True:
    answer = raw_input(prompt)
    if answer not in posscards:
        prompt = "not a possible card - try again: "
    elif answer in deck1:
        prompt = "you've already had that one - try again: "
    else:
        deck1.append(answer)
        break

It might be a little more readable if you factored it out into a function:

def get_card():
    while True:
        answer = raw_input(prompt)
        if answer not in posscards:
            prompt = "not a possible card - try again: "
        elif answer in deck1:
            prompt = "you've already had that one - try again: "
        else:
            return answer

Now, every time you call get_card, it's guaranteed to (eventually) return an answer. So, your main loop can look like this:

deck1 = []
for x in range(decksize):
    answer = get_card()
    deck1.append(answer)

And you can turn that into a one-liner:

deck1 = [get_card() for x in range(deck size)]

jramirez · Accepted Answer · 2013-11-14 22:26:22Z

0

by the way I don' see deck1 anywhere. make sure you declare before you try to append things to it.

deck1 = []

while answer not in posscards and answer in deck1:
     answer = raw_input("not a possible card or card already entered- try again: ")

answered Nov 14, 2013 at 22:26

jramirez

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