input: Write a function to rewrite the given Python code by introducing list comprehensions. The original code initializes an empty list and then appends even numbers from 1 to 20 using a for loop and a conditional check. The rewritten code should use a list comprehension to achieve the same result.
  
  def rewrite_to_list_comprehension(code_str):
      # Function implementation here
      pass
  
  assert rewrite_to_list_comprehension("""even_numbers = []
  for i in range(1,21):
      if i % 2 == 0:
          even_numbers.append(i)""") == "[i for i in range(1, 21) if i % 2 == 0]"
  assert rewrite_to_list_comprehension("""odd_numbers = []
  for j in range(1,21):
      if j % 2 != 0:
          odd_numbers.append(j)""") == "[j for j in range(1, 21) if j % 2 != 0]"
  assert rewrite_to_list_comprehension("""squares = []
  for k in range(1,6):
      squares.append(k**2)""") == "[k**2 for k in range(1, 6)]"
  assert rewrite_to_list_comprehension("""multiples_of_3 = []
  for m in range(1,16):
      if m % 3 == 0:
          multiples_of_3.append(m)""") == "[m for m in range(1, 16) if m % 3 == 0]"
  assert rewrite_to_list_comprehension("") == ""
output: def rewrite_to_list_comprehension(code_str):
      if not code_str.strip():
          return ""
      lines = code_str.strip().split('\n')
      var_name = lines[0].split('=')[0].strip()
      start, end = lines[1].split('range(')[1].split(')')[0].split(',')
      start = int(start.strip())
      end = int(end.strip())
      if 'if' in lines[2]:
          condition = lines[2].split('if ')[1].split(':')[0].strip()
          return f"[{var_name.split('=')[0].strip()} for {var_name.split('=')[0].strip()} in range({start}, {end}) if {condition}]"
      else:
          return f"[{lines[2].split('.append(')[1].split(')')[0].strip()} for {var_name.split('=')[0].strip()} in range({start}, {end})]"