Ytukyg

I am trying to randomly iterate over a deck of cards with no repetition.

Following is the code:

import random



class Cards:



    # Where prefix d is Diamonds, h is Hearts, s is Spades and c is Clubs

    total_cards = [{2: 'd2', 3: 'd3', 4: 'd4', 5: 'd5', 6: 'd6', 7: 'd7', 8: 'd8', 9: 'd9', 10: 'd10', 11: 'dJack',

              12: 'dQueen', 13: 'dKing', 14: 'dAce'},

             {2: 'h2', 3: 'h3', 4: 'h4', 5: 'h5', 6: 'h6', 7: 'h7', 8: 'h8', 9: 'h9', 10: 'h10', 11: 'hJack',

              12: 'hQueen', 13: 'hKing', 14: 'hAce'},

             {2: 's2', 3: 's3', 4: 's4', 5: 's5', 6: 's6', 7: 's7', 8: 's8', 9: 's9', 10: 's10', 11: 'sJack',

              12: 'sQueen', 13: 'sKing', 14: 'sAce'},

             {2: 'c2', 3: 'c3', 4: 'c4', 5: 'c5', 6: 'c6', 7: 'c7', 8: 'c8', 9: 'c9', 10: 'c10', 11: 'cJack',

              12: 'cQueen', 13: 'cKing', 14: 'cAce'}]



    def random_pick(self): # Method to randomly pick a card from the deck



        choice = random.choice(random.choice(self.total_cards))



        for v in self.total_cards:    # to retrieve the corresponding `key` for `choice` 

            for i in v.values():

                if choice == i:

                    k = v[i]

                    v.pop(k)



        print(choice)    # To print the random card picked from the deck

        print(self.total_cards)    # To print the updated Deck after picking the card





c = Cards()

c.random_pick()

The idea that I am trying to work with is, as soon as the card is picked, it should be removed from the deck.

This is the error :

Traceback (most recent call last):

  File "F:/Blackjack/Base/Cards.py", line 30, in <module>

    c.random_pick()

  File "F:/Blackjack/Base/Cards.py", line 17, in random_pick

    choice = random.choice(random.choice(self.total_cards))

  File "C:UsersPythonPython37-32librandom.py", line 262, in choice

    return seq[i]

KeyError: 0

From my understanding, KeyError is an exception raised when a mapping (dictionary) key is not found in the set of existing keys. But my IF LOOP is TRUE only when the condition choice == i and only then should the pop() be initiated.

I have tried the above code without the pop() method in the code and the code works just fine, generating random cards after every run.

If you try your code several times, you'll notice that you won't get this error every time. Sometimes it'll get past the line

        choice = random.choice(random.choice(self.total_cards))

and hit another error later in the code.

So what's going on? I assume that random.choice(self.total_cards) works fine and returns one of the four decks from the total_cards list. You represent that deck as a dictionary.

Let's see what random.choice does with dictionaries on a simpler example:

>>> import random

>>>

>>> random.seed(0)  # for reproducability

>>> random.choice({1:2, 3:4})

2

Huh, strange, it returned one of the values. I'd have expected one of the keys, like when iterating over a dictionary without calling .items() nor .values().

>>> [i for i in {1:2, 3:4}]

[1, 3]

Let's try again:

>>> random.seed(42)  # for reproducability

>>> random.choice({1:2, 3:4})

KeyError: 0

Strange, isn't it? 0 is neither among the values nor among the keys here. Where did it come from?

Let's see how random.choice is implemented. In IPython I can get its source code like this:

In [1]: import random



In [2]: random.choice??

To get the code on your system, you can also look at the file mentioned in the error message you got: C:UsersPythonPython37-32librandom.py around line 262.

On Python 3.6.6 (the version on my system) the source code is:

    def choice(self, seq):

        """Choose a random element from a non-empty sequence."""

        try:

            i = self._randbelow(len(seq))

        except ValueError:

            raise IndexError('Cannot choose from an empty sequence') from None

        return seq[i]

private method random._randbelow has the description

Return a random int in the range [0,n). Raises ValueError if n==0.

While this works fine for sequences (like lists, sets or tuples), I guess you can see why it won't do the right thing at all when seq happens to be a dictionary (or any other mapping):

It takes

the length of the sequence (len(seq))

(which works fine for dictionaries, too) and then

generates a random integer between 0 (inclusive) and that length (exclusive) (that's what self._randbelow does)

so this will be the

0-indexed position of a random element of the sequence

and then it

uses that random integer to index the sequence (seq[i]) and returns that value (return)

which doesn't work on dictionaries as intended because they are

indexed by their keys.

That's also why we sometimes didn't get the error and instead one of the dictionary values was returned by random.choice: When the integer intended as a

random position

also happened to be one of the keys of the dictionary, it would just return the corresponding value. If it happens to be none of our keys (which b.t.w. would always be the case, if all the keys were non-integers, e.g. strings) then a KeyError occurs.

Quick answer: random.choice() is meant for sequences i.e. lists, as it says in documentation.

Long answer: See das-g's answer.

I think a list would be better, here is how I would do it:

from random import shuffle



class Cards:



def __init__(self): #example deck with just some cards

    self.total_cards = ['c2', 'c3', 'c4', 'c5', 'c6', 'c7', 'c8', 'c9', 'c10']

    shuffle(self.total_cards)  #shuffle the deck of cards



def random_pick(self): #Method to randomly pick a card from the deck



    print(self.total_cards[len(self.total_cards)-1])    #To print the last card from your deck, which will be removed by pop() command

    self.total_cards.pop()

    print(self.total_cards)    #To print the updated Deck after pop() the last card





c = Cards()

for _ in range(3): # picking 3 random cards for demostration

    c.random_pick()

Try my solution:

import random

import numpy as np



class Cards:



    # Where prefix d is Diamonds, h is Hearts, s is Spades and c is Clubs

    total_cards = [{2: 'd2', 3: 'd3', 4: 'd4', 5: 'd5', 6: 'd6', 7: 'd7', 8: 'd8', 9: 'd9', 10: 'd10', 11: 'dJack',

          12: 'dQueen', 13: 'dKing', 14: 'dAce'},

         {2: 'h2', 3: 'h3', 4: 'h4', 5: 'h5', 6: 'h6', 7: 'h7', 8: 'h8', 9: 'h9', 10: 'h10', 11: 'hJack',

          12: 'hQueen', 13: 'hKing', 14: 'hAce'},

         {2: 's2', 3: 's3', 4: 's4', 5: 's5', 6: 's6', 7: 's7', 8: 's8', 9: 's9', 10: 's10', 11: 'sJack',

          12: 'sQueen', 13: 'sKing', 14: 'sAce'},

         {2: 'c2', 3: 'c3', 4: 'c4', 5: 'c5', 6: 'c6', 7: 'c7', 8: 'c8', 9: 'c9', 10: 'c10', 11: 'cJack',

          12: 'cQueen', 13: 'cKing', 14: 'cAce'}]

    _showed = 0



    def __init__(self):

        self._shuffle_cards()

        self.pointers = [0 for _ in range(len(self.total_cards))]



    def _shuffle_cards(self):

        for i, v in enumerate(self.total_cards):

            temp = list(v.items())

            self._showed += 1

            np.random.shuffle(temp)

            self.total_cards[i] = temp



    def random_pick(self):

        choice = random.choice(range(len(self.total_cards)))

        while self.pointers[choice] >= len(self.total_cards[choice]) and self._showed > 0: 

            choice = random.choice(self.total_cards)

            self.pointers[choice] += 1

        if self._showed == 0:

            print('Nothing cards to show')

        else:

            self._showed -= 1

            print(self.total_cards[choice][self.pointers[choice]][1])





c = Cards()

c.random_pick()