Make a list of random numbers in python without using numbers in another list

Question

I am trying to make a card game and I want to be able to generate random numbers in a list but I do not want the numbers to repeat themselves after they have been used once while the program is running.

Here is what I have so far:

usedcards = []
import random

def choosecards():
    global usedcards
    cards=random.sample(range(52), 5)
    usedcards = usedcards + cards
    #print(usedcards)
    return cards

Each time I run the function, I want the usedcards list to be cross checked with the cards variable.

How can I make this happen?

Just make a list of available cards, shuffle it (random.shuffle()) and .pop() a card when you need one. — Klaus D.
– Klaus D., Commented Jan 12, 2016 at 23:55

Marius · Accepted Answer · 2016-01-12 23:57:50Z

4

Here is one way to do this using sets. Sets make it very easy to exclude the cards that have already been used.

import random

used_cards = set()

def choose_cards(n_cards):
    # No need to do 'global used_cards', used_cards is
    #    already global and can be modified inplace
    # Find the set difference between all the cards and
    #   those that have been used
    available = set(range(52)) - used_cards
    chosen = random.sample(available, n_cards)
    for card in chosen:
        used_cards.add(card)
    return chosen


for i in range(4):
    print(choose_cards(5))
    print(used_cards)

answered Jan 12, 2016 at 23:57

Marius

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1 Comment

Copperfield Over a year ago

you can also use used_cards.update(chosen) to avoid the for-loop

Mike Müller · Accepted Answer · 2016-01-13 00:21:56Z

3

A generator can keep the state and hide the details:

import random

def choosecards(amount=5):
    cards = list(range(52))
    random.shuffle(cards)
    while True:
        yield [cards.pop() for _ in range(amount)]


>>> cards = choosecards()
>> next(cards)
[37, 41, 13, 2, 33]
>>> next(cards)
[4, 8, 7, 38, 23]

edited Jan 13, 2016 at 0:21

answered Jan 13, 2016 at 0:04

Mike Müller

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Comments

Chad S. · Accepted Answer · 2016-01-13 00:12:40Z

2

don't use globals. The problem becomes easy to solve if you use parameters properly.

def choosecards(stack, amount=5):
    cards=[ stack.pop() for i in range(amount) ]
    return cards


deck = list(range(52))
random.shuffle(deck)
hand = choosecards(deck)
otherhand = choosecards(deck)
#etc.

edited Jan 13, 2016 at 0:12

answered Jan 12, 2016 at 23:58

Chad S.

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1 Comment

John La Rooy Over a year ago

I think you mean stack.pop()

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