Python random’s shuffle method to randomizes the sequence items

In this article, we will learn how to use the shuffle method of a random module to shuffle the data. In this article, we will learn how randomly Shuffle List and String in Python. Shuffle any sequence in place or not in place.

The Syntax of random.shuffle

Following is the syntax of a shuffle method.

random.shuffle(x, random)

Shuffle method takes two parameters. Out of the two random is an optional parameter. Shuffle method used to shuffle the sequence in place. i.e., it changes the position of items in a list. We call it a randomizes the elements of a list in place.

Examples: Shuffling a pack of cards, shuffling list of a string.

Arguments: –

• x is any sequence you want to shuffle. x can be the list, String or tuple.
• The optional argument random is a 0-argument function returning a random float number between 0.1 to 1.0 If not specified by default, this is the function random().
• If you want to perform shuffling as per your need then you can pass your custom random function in the place of random argument, which will dictate shuffle method how to randomizes the items of a list.

Return Value

The random.shuffle shuffles in place and doesn’t return anything i.e., It returns None.

It reshuffles the original list (change the items positions). If you print the original list after calling the shuffle method, you will find the elements positions changed.

Python shuffle a list using random.shuffle

Let see how to shuffle list in place using a random.shuffle method.

import random

number_list = [7, 14, 21, 28, 35, 42, 49, 56, 63, 70]
print ("Original list : ",  number_list)

random.shuffle(number_list) #shuffle method
print ("List after first shuffle  : ",  number_list)

random.shuffle(number_list)
print ("List after second shuffle : ",  number_list)

You can get the following output:  Execute Online

Original list :  [7, 14, 21, 28, 35, 42, 49, 56, 63, 70]
List after first shuffle  :  [7, 14, 56, 21, 35, 70, 49, 42, 28, 63]
List after second shuffle :  [35, 63, 70, 21, 42, 28, 49, 56, 14, 7]

As you can see in the output list items positions are changed.

Shuffle a list of Strings using random.shuffle()

It works same as above example.

import random

string_list = ["Paint It Black", "Gimme Shelter", "Sympathy for the Devil", "Satisfaction", "You Cant Always Get What You Want"]
print ("Original String list: ",  string_list)

random.shuffle(string_list) #shuffle method
print ("String List after the first shuffle  : ",  string_list)

random.shuffle(string_list)
print ("String List after the second shuffle : ",  string_list)

Output:  Execute Online

Original String list :  ['Paint It Black', 'Gimme Shelter', 'Sympathy for the Devil', 'Satisfaction', 'You Cant Always Get What You Want']
String List after the first shuffle  :  ['Gimme Shelter', 'Satisfaction', 'Sympathy for the Devil', 'You Cant Always Get What You Want', 'Paint It Black']
String List after the second shuffle :  ['Paint It Black', 'Gimme Shelter', 'Sympathy for the Devil', 'Satisfaction', 'You Cant Always Get What You Want']

Python shuffling list to get the same result every time

How to shuffle list with a parameter such that the shuffling produces the same result every time?

Using the random.seed() method of a random module it is possible that the shuffling produces the same result every time. Let see how to use a seed method with the shuffle method.

numbers = [10, 20, 30, 40, 50, 60]
print ("Original list: ", numbers )
random.seed(4)
random.shuffle(numbers)
print("reshuffled list ", numbers)

numbers = [10, 20, 30, 40, 50, 60]
random.seed(4)
random.shuffle(numbers)
print("reshuffled list ", numbers)

Output:  Execute Online

Original list:  [10, 20, 30, 40, 50, 60]
reshuffled list  [40, 60, 50, 10, 30, 20]
reshuffled list  [40, 60, 50, 10, 30, 20]

Python random’s shuffle not-in-place

As we already discussed the random.shuffle shuffles in place and didn’t return anything. So let see now how to shuffle list not in-place.

To perform shuffle not in-place we need to use a simple method of random module.

random.sample()  method returns the new list with the number of sample size you passed to it. If we pass the sample size same as the size of a list it will return us the new list which is shuffled version of the original list. Let do this with an example.

import random

numbers = [5, 10, 15, 20, 25]
print ("Original list : ",  numbers)

new_list = random.sample(numbers, len(numbers))
print ("List after not in-place shuffle  : ",  new_list)

Output:  Execute Online

Original list :  [5, 10, 15, 20, 25]
List after not in-place shuffle  :  [5, 20, 10, 15, 25]

As you can see we used a sample method to perform not in-place shuffle.

Shuffling a string in Python

The random.shuffle doesn’t’ work with String. I.e., It can’t accept string argument. If you try to execute the following, you will get an error.

import random

string_one = "pynative"
random.shuffle(string_one)
print(string_one)

You will get the TypeError: 'str' object does not support item assignment. Then how to shuffle characters of a string.

We can do this using various approaches. Let discuss each one by one.

Approach One

• Convert String into a list of characters.
• shuffle the list of characters randomly.
• Convert the shuffled list into String.

import random

string_one = "pynative"
print ("Original String: ", string_one)

char_list = list(string_one) # convert string inti list

random.shuffle(char_list) #shuffle the list

string_one = ''.join(char_list)
print ("shuffled String is: ", string_one)

Output:  Execute Online

Original String:  pynative
shuffled String is:  anvtipye

Shuffle two Python List at once with the same order

Let’s assume if you want to Shuffle two list but also wants to maintain the same shuffle order. For example, One list contains employee name and other contains salary.

import random

empName = ['Jhon', 'Emma', 'Kelly', 'Jason']
empSalary = [7000, 6500, 9000, 10000]

print("Print Lists Before Shuffling")
print("List Employee Names: ", empName)
print("List Employee Salary: ", empSalary)

mapIndexPosition = list(zip(empName, empSalary))
random.shuffle(mapIndexPosition)
empName, empSalary = zip(*mapIndexPosition)

print("\nPrint Lists after Shuffling")
print("List Employee Names: ", empName)
print("List Employee Salary: ", empSalary)

Output:  Execute Online

Print Lists Before Shuffling
List Employee Names:  ['Jhon', 'Emma', 'Kelly', 'Jason']
List Employee Salary:  [7000, 6500, 9000, 10000]

Print Lists after Shuffling
List Employee Names:  ('Emma', 'Jhon', 'Kelly', 'Jason')
List Employee Salary:  (6500, 7000, 9000, 10000)

Shuffling multidimensional array in Python

Let’s assume if you have a multidimensional array and want to shuffle it. In this example, I am using Numpy module to create a 2-d array. Also, Using numpy.random.shuffle() method we can shuffle the multidimensional array.
Now, Let’s see how to shuffle a multidimensional array in Python.

import numpy

print("Before Shufflling 2-dimensional array in Python")
sampleArray = numpy.arange(100, 240, 10)
sampleArray = sampleArray.reshape(7,2)
print (sampleArray)

print("After Shufflling 2-dimensional array in Python")
newArray = numpy.random.shuffle(sampleArray)
print (sampleArray)

Output:  Execute Online

Before Shufflling 2-dimensional array in Python
[[100 110]
 [120 130]
 [140 150]
 [160 170]
 [180 190]
 [200 210]
 [220 230]]
After Shufflling 2-dimensional array in Python
[[120 130]
 [140 150]
 [160 170]
 [180 190]
 [220 230]
 [100 110]
 [200 210]]

Shuffle a dictionary in Python

Shuffling a dictionary is not possible in Python. However, we can rearrange the iteration order of keys of a dictionary.  Fetch all keys from a dictionary and add it in a list, shuffle that list and access dictionary values using newly shuffled keys.

import random

studentDict = {'Eric':80, 'Scott':75, 'Jessa':95, 'Mike':66}
print("Dictionary Before Shuffling")
print(studentDict)
keys =  list(studentDict.keys())
random.shuffle(keys)

ShuffledStudentDict = dict()
for key in keys:
  ShuffledStudentDict.update({key:studentDict[key]})

print("\nDictionary after Shuffling")
print(ShuffledStudentDict)

Output:  Execute Online

Dictionary Before Shuffling
{'Eric': 80, 'Scott': 75, 'Jessa': 95, 'Mike': 66}

Dictionary after Shuffling
{'Jessa': 95, 'Eric': 80, 'Mike': 66, 'Scott': 75}

Next Steps

To practice what you learned in this article, I have created a Python random data generation Quiz and Exercise project.

Let me know your comments and feedback in the section below.