CODEWITHSUNDEEP
pythonlist
user
user

Reputation: 159

how to shuffle items of a list using python?

I want to riffle shuffle items of a list without necessary importing any module. So a function should return a riffle shuffled list, riffle shuffle is where it will first break it into two lists then interleave them into one list.

for example the list= [ a, b ,c ,d]

should be [ c,a,d,b] or [a, c,b,d] after riffle shuffling it

Upvotes: 0

Views: 751

Answers (3)

RickyA
RickyA

Reputation: 16029

This is fun! No imports!

The problem is that we need a coin flip without importing anything. Sounds like a test for <some random int> % 2 == 0. The hard part is <some random int>. A pointer on the heap maybe?

input_list = ['a', 'b', 'c', 'd']

#you should empty this once and awhile
fill_my_heap = [] 

#nothing to see here
class Dummy(): 
    pass

for x in range(0,10):    
    #give me a new pointer
    foo = Dummy()
    #prevent reuse of heap memory location
    fill_my_heap.append(foo) 
    #get id of new class and strip its last digit because that was always even
    ptr_int = int(str(id(foo))[:-1]) 
    #test to see if this is even. Should be 50% of the time. Sort of... ;)
    is_even = ptr_int%2==0 
    #split list
    a = input_list[:len(input_list)/2]
    b = input_list[len(input_list)/2:]
    #and assemble output based on even-switch
    if is_even:
        output = a + b
    else:
        output = b + a
    print(output)

Gives:

['a', 'b', 'c', 'd']
['a', 'b', 'c', 'd']
['a', 'b', 'c', 'd']
['c', 'd', 'a', 'b']
['a', 'b', 'c', 'd']
['a', 'b', 'c', 'd']
['c', 'd', 'a', 'b']
['a', 'b', 'c', 'd']
['c', 'd', 'a', 'b']
['a', 'b', 'c', 'd']

Upvotes: 1

georg
georg

Reputation: 214969

If you don't like imports, a simple LCG is pretty straightforward to code:

def lcg(_):
    lcg.val = (1664525 * lcg.val + 1013904223) & 0xffffffff
    return lcg.val

lcg.val = id('') # seed

and then:

print sorted(range(52), key=lcg)

Upvotes: 0

John La Rooy
John La Rooy

Reputation: 304175

Python2 version

cards = range(52)
a = cards[:len(cards)/2]
b = cards[len(cards)/2:]
if id('')/0xffff&1:
    a, b = b, a
cards[::2] = a
cards[1::2] = b
print cards

Python3 version

cards = list(range(52))
a = cards[:len(cards)//2]
b = cards[len(cards)//2:]
if id('')//0xffff&1:
    a, b = b, a
cards[::2] = a
cards[1::2] = b
print(cards)

Upvotes: 3

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