Question

I have a dictionary: dict = {"key":[None, "item 2", "item 3"]}

How can I check that dict["key"][0] is None if “key” is unknown.

I have this so far:

{k: dict[k][0] for k in dict.viewkeys()}

which gives me:

{"key":None}

In my application, I am testing to see if dict["key"][0] has been populated yet, its default is None.

Answer 1

You’re very close. If you want all key, value pairs such that the first item in the value list is None, you could do this:

unassigned_items = {k:v for k, v in mydict.viewitems() if v[0] is None}

Note that you shouldn’t use dict as a variable name because it masks the dict built-in — even in example code, if only because it may mislead people.

Once you’ve got unassigned_items, you can simply test to see if 'key' is in unassigned_items:

if key in unassigned_items:
    do_something()