How to shuffle a string in python without using shuffle

I'm trying to scramble a string, "string", without using random.shuffle(), but my code keeps producing output that has missing and repeating characters, e.g. gtrgtg, gnrtnn, etc. I'm not sure what I'm doing wrong.

    import random
    s = "string"
    new_s=[]
    for c in s:
      if random.choice(s) not in new_s:
        new_s.append(random.choice(s))

    print(''.join(new_s))

asked Dec 24, 2017 at 15:51

In its current state, your program checks whether the randomly chosen character is in a string. If it is, it doesn't do anything other than continuing the loop. Also since you don't assign random.choice(s) to a variable, you generate another character after you do the check.

A working version would be:

import random
s = "string"
new_s = []
for c in s:
    char = random.choice(s)  # assign it to a variable
    while char in new_s:  # until a new character comes, repeat the procedure
        char = random.choice(s)
    new_s.append(char)

print(''.join(new_s))

This generates strings like ngtsri, gsrnit, etc. Note that this won't work if you have duplicates in the original string.

The above code is highly inefficient. I only gave the correction assuming this was for learning purposes. Normally, if you want to repeatedly check if something is in a collection, that collection should be a set or a dictionary.

answered Dec 24, 2017 at 16:03

ayhanayhan

66.2k17 gold badges173 silver badges191 bronze badges

0

random.choice choses a random character out of string s, but doesn't remove it - so it's possible for the same character to be chosen multiple times, and for some characters to not be chosen at all.

import random

s = 'string'
new_s = []

# rather than choosing a character, chose an index, use it and slice it out
while s:
    i = random.randint(0, len(s)-1)
    new_s.append(s[i])
    s = s[:i] + s[i+1:]
print(''.join(new_s))

# this is more elegant with lists:
s = list(s)
while s:
    i = random.randint(0, len(s)-1)
    new_s.append(s.pop(i))
print(''.join(new_s))

Neither option is very efficient... but for efficiency, use random.shuffle. :)

answered Dec 24, 2017 at 16:01

Dan GittikDan Gittik

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Using while, you could loop through s until the length of new_s matches with that of s and the resultant string has non-repeating characters.

import random

s = "string"
new_s = ''  # So you will not need ''.join() when you print this result

while len(new_s) != len(s):
    char = random.choice(s)
    if char not in new_s:
        new_s += char

print(new_s)

rntigs
>>> 

answered Dec 24, 2017 at 20:19

srikavineeharisrikavineehari

2,4041 gold badge10 silver badges21 bronze badges

try this:

from random import randint

def shuffle(sr):
    n = len(sr)
    s = list(sr)
    for i in range(n):
        cur, idx = s[i], randint(0, n - 1)
        s[i], s[idx] = s[idx], cur
    return ''.join(s)

print(shuffle("hello"))

answered Dec 24, 2017 at 15:57

mehdi maickmehdi maick

3253 silver badges7 bronze badges

In Python, you can shuffle (= randomize) a list, string, and tuple with random.shuffle() and random.sample().

• random — Generate pseudo-random numbers — Python 3.8.1 documentation

random.shuffle() shuffles a list in place, and random.sample() returns a new randomized list. random.sample() can also be used for a string and tuple.

• random.shuffle() shuffles a list in place
• random.sample() returns a new shuffled list
• How to shuffle a string and tuple
• Initialize the random number generator with random.seed()

If you want to sort in ascending or descending order or reverse instead of shuffling, see the following articles.

• Sort a list, string, tuple in Python (sort, sorted)
• Reverse a list, string, tuple in Python (reverse, reversed)

random.shuffle() shuffles a list in place

You can shuffle a list in place with random.shuffle().

import random

l = list(range(5))
print(l)
# [0, 1, 2, 3, 4]

random.shuffle(l)
print(l)
# [1, 0, 4, 3, 2]

random.sample() returns a new shuffled list

random.sample() returns a new shuffled list. The original list remains unchanged.

random.sample() returns random elements from a list. Pass the list to the first argument and the number of elements to return to the second argument. See the following article for details.

• Random sampling from a list in Python (random.choice, sample, choices)

By setting the total number of elements in the list to the second argument, random.sample() returns a new list with all elements randomly shuffled. You can get the total number of elements in the list with len().

l = list(range(5))
print(l)
# [0, 1, 2, 3, 4]

lr = random.sample(l, len(l))
print(lr)
# [0, 3, 1, 4, 2]

print(l)
# [0, 1, 2, 3, 4]

How to shuffle a string and tuple

Strings and tuples are immutable, so random.shuffle() that modifies the original object raises an error TypeError.

s = 'abcde'

# random.shuffle(s)
# TypeError: 'str' object does not support item assignment

t = tuple(range(5))
print(t)
# (0, 1, 2, 3, 4)

# random.shuffle(t)
# TypeError: 'tuple' object does not support item assignment

To shuffle strings or tuples, use random.sample(), which creates a new object.

random.sample() returns a list even when a string or tuple is specified to the first argument, so it is necessary to convert it to a string or tuple.

For strings, a list of characters is returned. Use the join() method to concatenate to a single string again.

• Concatenate strings in Python (+ operator, join, etc.)

sr = ''.join(random.sample(s, len(s)))
print(sr)
# bedca

Use tuple() for tuples, which creates a tuple from a list.

• Convert list and tuple to each other in Python

tr = tuple(random.sample(t, len(l)))
print(tr)
# (0, 1, 2, 4, 3)

Initialize the random number generator with random.seed()

You can initialize a random number generator with random.seed().

After initializing with the same seed, it is shuffled in the same way.

l = list(range(5))
random.seed(0)
random.shuffle(l)
print(l)
# [2, 1, 0, 4, 3]

l = list(range(5))
random.seed(0)
random.shuffle(l)
print(l)
# [2, 1, 0, 4, 3]

How do you randomize a string in Python?

How do you randomize data in Python?

How can you randomize the items of a list in place in Python?

Do we have any inbuilt function for shuffling the values of list?