Python Only Response Morse Code

Morse Code is delivered in a series signals which are referred to as dashes (-) or dots (.). To keep things simple for the purposes of this challenge we'll only decode letters with a maximum length of three signals.

1:1

Here is the Morse Code dichotomic search table courtesy of Wikipedia

Morse Code Examples

-.- translates to K ... translates to S .- translates to A -- translates to M . translates to E

Background

You've started work as morse code translator. Unfortunately some of the signals aren't as distinguishable as others and there are times where a . seems indistinguishable from -. In these cases you write down a ? so that you can figure out what all the posibilities of that letter for that word are later.

Task

Write a function possibilities that will take a string word and return an array of possible characters that the morse code word could represent.

Examples with ?

? should return ['E','T'] ?. should return ['I','N'] .? should return ['I','A'] ?-? should return ['R','W','G','O']

Dot Dash start R (W