input: Write a function to generate a random 6-digit number in Python. If the input is provided, return the number as a string; otherwise, return it as an integer.
  assert generate_random_number('include_string')=='123456'
  assert generate_random_number('not_include_string')==123456
  assert generate_random_number(None)==123456
  assert generate_random_number(True)==123456
output: import random
  
  def generate_random_number(input_type=None):
      random_number = random.randint(100000, 999999)
      if input_type == 'include_string':
          return str(random_number)
      else:
          return random_number