Python nested dict comprehension with if else

Question

I am trying to convert the below to a dict comprehension

my_dict = {'a': None, 'b': None, 'c': ['1', '2', '3']}
new_dict = {}
 for k, v in my_dict.items():
     if not v:
         new_dict[k] = None
     else:
         for item in v:
             new_dict[f'{k}{item}'] = None

I'm trying to translate my dict to

new_dict = {'a': None, 'b': None, 'c1': None, 'c2': None, 'c3': None}

I'm fairly comfortable with basic list and dict comprehensions but struggling with this one, currently looking something like this but clearly I am a bit off on the syntax:

{k: None if not v else f'{k}{item}': None for item in v for k, v in my_dict.items()}

Answer 1

This abomination will do:

{fk: None
 for k, v in my_dict.items()
 for fk in ([k] if v is None else (k + fv for fv in v))}

If the value is None, you just want the key.
If the value is not None, you want a list of each value concatenated with the key.
Homogenise that to always returning a list, either of one key or multiple:

[k] if v is None else [k + fv for fv in v]

Then you're looking at a "simple" nested comprehension:

{k: None for k in [['a'], ['b'], ['c1', 'c2', 'c3']] for fk in k}