input: Write a python function to check if Python is installed using bash command.
  assert check_python_installed() == 'Python is installed!'
output: def check_python_installed():
      import subprocess
      try:
          result = subprocess.run(['python', '--version'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
          if result.returncode == 0:
              return 'Python is installed!'
          else:
              return 'Python is not installed!'
      except FileNotFoundError:
          return 'Python is not installed!'