如何从已有的字典中有选择地创建字典？

existing_dict = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
selected_dict = {k: v for k, v in existing_dict.items() if k in ['a', 'b']}
print(selected_dict)

existing_dict = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
selected_dict = dict(filter(lambda x: x[0] in ['a', 'b'], existing_dict.items()))
print(selected_dict)

existing_dict = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
selected_dict = {}
for k, v in existing_dict.items():
    if k in ['a', 'b']:
        selected_dict[k] = v
print(selected_dict)