How to loop though range and randomly shuffle a list in Python?

Question

Given a list x = [1,0,0,1,1]I can use random.shuffle(x) repeatedly to shuffle this list, but if I try to do this a for loop the list doesn't shuffle.

For example:

x = [1,0,0,1,1]
k = []
for i in range(10):
     random.shuffle(x)
     k.append(x)
return x

Basically, kcontains the same sequence of x unshuffled? Any work around?

Answer 1

One pythonic way to create new random-orderings of a list is not to shuffle in place at all. Here is one implementation:

[random.sample(x, len(x)) for _ in range(10)]

Explanation

• random.sample creates a new list, rather than shuffling in place.
• len(x) is the size of the sample. In this case, we wish to output lists of the same length as the original list.
• List comprehensions are often considered pythonic versus explicit for loops.

Answer 2

As mentioned by @jonrsharpe, random.shuffle acts on the list in place. When you append x, you are appending the reference to that specific object. As such, at the end of the loop, k contains ten pointers to the same object!

To correct this, simply create a new copy of the list each iteration, as follows. This is done by calling list() when appending.

import random
x = [1,0,0,1,1]
k = []
for i in range(10):
     random.shuffle(x)
     k.append(list(x))