Generating a series of random strings can help create security codes. Besides, there are many other applications for using a random string generator, for instance, obtaining a series of numbers for a lottery game or slot machines. A random string generator generates an alphanumeric string consisting of random characters and digits. Let's see how we can create a random string generator.

Method 1: Using for loop

For generating random strings only with uppercase letters and digits using for loop, we require to import built-in python modules, namely random and string.

# Random string generation using uppercase letters and digits
# YTDWIU75
import random
import string


def id_generator(length):

    # initializing empty string
    return_str = ""

    # generating a string containing A-Z and 0-9
    data = string.ascii_uppercase + '0123456789'

    for i in range(length):

        # generating random strings
        return_str += random.choice(data)

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


# function call
id_generator(7)

The generated random string : 0ZM1C29

Method 2: Using secrets.choice()

The secrets module generates cryptographically secure random numbers suitable for managing data such as passwords, account authentication, and security tokens.

import secrets
import string

# initializing empty string
return_str = ""
  
# initializing size of string
N = 7

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

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

The generated random string : 26SJ8IA

Method 3: Using random.choices()

The third approach is by random.choices. The choices() function returns a collection of random elements with replacement.

import random
import string

# initializing empty string
return_str = ""
  
# initializing size of string
N = 7

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

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

The generated random string : H4ICGAZ

Method 4: Using secrets module

 step-by-step algorithm for implementing this approach:

1. Import the secrets and string modules.
2. Define the id_generator function with a single argument, length.
3. Initialize an empty string, return_str.
4. Generate a string containing uppercase letters and digits (0-9) using string.ascii_uppercase and the string literal '0123456789'.
5. Use a list comprehension to generate a list of length random characters from the data string using secrets.choice(data).
6. Use the join method to concatenate the characters in the list into a single string.
7. Assign the resulting string to return_str.
8. Print the generated random string with a message.
9. Return the generated string.

import secrets
import string

def id_generator(length):

    # initializing empty string
    return_str = ""

    # generating a string containing A-Z and 0-9
    data = string.ascii_uppercase + '0123456789'

    # using the secrets module to generate the random string
    return_str = ''.join(secrets.choice(data) for i in range(length))

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

# function call
id_generator(7)

The generated random string : YB7HXVH

The time complexity of this algorithm is O(n), where n is the length of the string to be generated. The secrets.choice() method is called n times to generate the random characters, and the join() method is called once to concatenate the characters into a string.

The auxiliary space of this algorithm is also O(n), where n is the length of the string to be generated. This is because the function creates a list of length n to hold the random characters, and then concatenates them into a string of length n. The space used by the data string and the return_str variable is constant, regardless of the length of the generated string.