Random without repetition?

Question

I want to write a program that displays all the elements of a list in random order without repetition. It seems to me that it should work, but only prints those elements with repetition.

import random

tab = []

for i in range(1, 8):
    item = random.choice(["house", "word", "computer", "table", "cat", "enter", "space"])
    if item not in tab:
        print(item)
    else:
        tab.append(item)
        continue

possible duplicate of [Shuffling a list of objects in python](http://stackoverflow.com/questions/976882/shuffling-a-list-of-objects-in-python) — awesoon, Jun 09 '15 at 15:06

Anshul Goyal · Answer 1 · 2015-06-09T15:31:10.050

Instead of random.choice within the for loop, use random.shuffle here.

This way, your list is guaranteed to be have all the elements, while also maintaining the requirement of random order:

>>> import random
>>> tab = ["house", "word", "computer", "table", "cat", "enter", "space"]
>>> random.shuffle(tab)
>>> print tab

As for your original code, that will not work, since the if else block as you've written ensures that no element is added within the list tab. You could correct that by removing the else block like below:

>>> for i in range(1, 8):
...     item = random.choice(["house", "word", "computer", "table", "cat", "enter", "space"])
...     if item not in tab:
...         print(item)
...         tab.append(item)
... 
house
cat
space
enter

But now you will need to alter the logic so that the runs in which same value is randomly returned don't affect the number of outputs.

DanteVoronoi · Answer 2 · 2015-06-09T15:13:54.097

6

Read about capabilities of Random library. It can write simpler. For example:

import random

data = ["house", "word", "computer", "table", "cat", "enter", "space"]
x = random.sample(data, len(data))
print(x)

edited Jun 09 '15 at 15:13

answered Jun 09 '15 at 15:07

DanteVoronoi

1,133
1
13
20

score 0 · Answer 3 · answered Jun 23 '20 at 22:11

0

import random
items = ["house", "word", "computer", "table", "cat", "enter", "space"]
tab= []
while len(tab) < len(items):
    item = random.choice(items)
    if item not in tab:
    tab.append(item)
print(tab)

answered Jun 23 '20 at 22:11

Rajko Jovicic

1
1

1

Ple add some description to this answer – Henry Harutyunyan Jun 23 '20 at 23:19

score 0 · Answer 4 · edited Apr 10 '21 at 07:19

As Anshul pointed out the use of random shuffle is great:

import random

options = ["house", "word", "computer", "table", "cat", "enter", "space"]
random.shuffle(options)
print (options)

If you however do not want to import the random library it is possible to solve the problem like below:

options_shuffled = []
options = ["house", "word", "computer", "table", "cat", "enter", "space"]
while len(options) > 0:
    random_bytes = open('/dev/urandom', 'rb').read(4)
    idx = int(int.from_bytes(random_bytes, 'big') / 2 ** (8 * 4) * len(options))
    options_shuffled.append(options[idx])
    del options[idx]

print (options_shuffled)

Random without repetition?

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