input: Write a python function to measure execution time of a sample code block.
  assert measure_time() >= 0
  assert isinstance(measure_time(), float)
output: def measure_time():
      import time
      start_time = time.time()
      # Sample code block
      for _ in range(1000000):
          pass
      end_time = time.time()
      return end_time - start_time