>>> marks = {
   'Ravi': 45.23,
   'Amar': 62.78,
   'Ishan': 20.55,
   'Hema': 67.20,
   'Balu': 90.75
}

>>> passed = { key:value for key, value in marks.items() if value > 50 }
>>> passed
{'Amar': 62.78, 'Hema': 67.2, 'Balu': 90.75}

>>> names = { 'Amar', 'Hema', 'Balu' }
>>> lst = { key:value for key,value in marks.items() if key in names}
>>> lst
{'Amar': 62.78, 'Hema': 67.2, 'Balu': 90.75}