Initializing a dictionary in python with a key value and no corresponding values

Question

I was wondering if there was a way to initialize a dictionary in python with keys but no corresponding values until I set them. Such as:

Definition = {\'apple\':         


        

Answer 1

It would be good to know what your purpose is, why you want to initialize the keys in the first place. I am not sure you need to do that at all.

1) If you want to count the number of occurrences of keys, you can just do:

Definition = {}
# ...
Definition[key] = Definition.get(key, 0) + 1

2) If you want to get None (or some other value) later for keys that you did not encounter, again you can just use the get() method:

Definition.get(key)  # returns None if key not stored
Definition.get(key, default_other_than_none)

3) For all other purposes, you can just use a list of the expected keys, and check if the keys found later match those.

For example, if you only want to store values for those keys:

expected_keys = ['apple', 'banana']
# ...
if key_found in expected_keys:
    Definition[key_found] = value

Or if you want to make sure all expected keys were found:

assert(all(key in Definition for key in expected_keys))