input: Write a function to print out every number from 0 to 10, but with every number being multiplied by 2.
  
  assert call_function()=='0\n2\n4\n6\n8\n10\n12\n14\n16\n18\n20\n'
  assert call_function()=='0\n2\n4\n6\n8\n10\n12\n14\n16\n18\n20\n'
  assert call_function()==call_function()
  assert call_function()==call_function()
  assert call_function()==call_function()
output: def call_function():
      result = ""
      for i in range(11):
          result += str(i * 2) + "\n"
      return result