Python | Generate random string of given length

The issue of generation of random numbers is quite common, but sometimes, we have applications that require us to better that and provide some functionality of generating a random string of digits and alphabets for applications such as passwords. Let’s discuss certain ways in which this can be performed in Python. Here, we will use Random string generation with upper case letters and digits

Method 1: Generate a random string using random.choices()

This random.choices() function of a random module can help us achieve this task, and provides a one-liner alternative to a whole loop that might be required for this particular task. Works with Python > v3.6. 

• String.ascii_uppercase – It returns the string with uppercase.
• String.digits – It returns the string with digits.
• String.punctuation – It returns the string with punctuations
• String.ascii_letters – It returns the string containing various cases.
• String.ascii_lowercase – It returns the string with lowercase.

Example 1: Random string generation with upper case letters

Python3

import string
import random

# initializing size of string
N = 7

# using random.choices()
# generating random strings
res = ''.join(random.choices(string.ascii_uppercase +
                             string.digits, k=N))

# print result
print("The generated random string : " + str(res))

Output :

The generated random string : 0D5YE91

Example 2: Generate a random string of a given length in Lowercase

Python3

import string
import random

# initializing size of string
N = 7

# using random.choices()
# generating random strings
res = ''.join(random.choices(string.ascii_lowercase +
                             string.digits, k=N))

# print result
print("The generated random string : " + str(res))

Output:

The generated random string : ipxktny

Example 3: Generate a random string of a given length in Uppercase and Lowercase

Python3

import string
import random

# initializing size of string
N = 7

# using random.choices()
# generating random strings
res = ''.join(random.choices(string.ascii_letters, k=N))

# print result
print("The generated random string : " + str(res))

Output:

The generated random string : ALpxvmI

Method 2: Generate random string using secrets.choice()

We can Generate Random Strings and Passwords in Python using secrets.choice(). For Cryptographically more secure random numbers, this function of the secret module can be used as its internal algorithm is framed in a way to generate less predictable random numbers.

Python3

import secrets
import string

# initializing size of string
N = 7

# using secrets.choice()
# generating random strings
res = ''.join(secrets.choice(string.ascii_uppercase + string.digits)
              for i in range(N))

# print result
print("The generated random string : " + str(res))

Output : 

The generated random string : T7HPKVR

Approach:

Import the necessary modules: random and string.
Define a function named generate_random_string that takes in a parameter length to determine the length of the random string to generate.
Use string.ascii_letters to get all the ASCII letters in lowercase and uppercase.
Use random.choice to randomly choose characters from letters for the given length of the string, and concatenate them using ”.join().
Return the generated string.
Use the function by passing in the desired length to generate a random string.

Python3

import random
import string

def generate_random_string(length):
    # Get all the ASCII letters in lowercase and uppercase
    letters = string.ascii_letters
    # Randomly choose characters from letters for the given length of the string
    random_string = ''.join(random.choice(letters) for i in range(length))
    return random_string

# Example usage: generate a random string of length 10
random_string = generate_random_string(10)
print(random_string)

Output

mFPltLThhj

Time complexity: O(n), where n is the length of the desired random string.

Auxiliary Space: O(n), where n is the length of the desired random string.