input: Write a function in Python to create a random string of a specified length. The function should take an integer as input representing the desired length of the string and return a string composed of random characters from the set of lowercase and uppercase letters and digits.
  
  ### Input:
  integer length
  
  ### Output:
  import random
  
  def generate_string(string_length):
      random_characters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
      random_string = ''.join(random.choices(random_characters, k=string_length))
      return random_string
  
  assert generate_string(10) != generate_string(10) # Different random strings
  assert len(generate_string(10)) == 10
output: def generate_string(string_length):
      random_characters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
      random_string = ''.join(random.choices(random_characters, k=string_length))
      return random_string