Dictionary value as function to be called when key is accessed, without using "()"

Question

I have a dictionary that has values sometimes as strings, and sometimes as a functions. For the values that are functions is there a way to execute the function without explicitly typing () when the key is accessed?

Example:

d = {1: "A", 2: "B", 3: fn_1}
d[3]() # To run function

I want:

d = {1: "A", 2: "B", 3: magic(fn_1)}
d[3] # To run function

Answer 1

Another possible solution, is to create a custom dictionary object that implements this behavior:

>>> class CallableDict(dict):
...     def __getitem__(self, key):
...         val = super().__getitem__(key)
...         if callable(val):
...             return val()
...         return val
...
>>>
>>> d = CallableDict({1: "A", 2: "B", 3: lambda: print('run')})
>>> d[1]
'A'
>>> d[3]
run

A perhaps more idiomatic solution would be to use try/except:

def __getitem__(self, key):
    val = super().__getitem__(key)
    try:
        return val()
    except TypeError:
        return val

Note however the method above is really for completness. I would not reccomend using it. As pointed out in the comments, it would mask TypeError's raised by the function. You could test the exact content of TypeError, but at that point, you'd be better of using the LBYL style.