sample.playground

// http://stackoverflow.com/questions/36744537/why-print-is-printing-my-string-as-an-optional

import UIKit

var input: [[String: AnyObject]] = [[:]]

input = [
    ["key": 101],
    ["key": 102],
    ["key": 103]
]

// This is what we want - the values from input to become String keys:
var desiredDictionary: [String: AnyObject] = [:]

desiredDictionary = [
    "101": "whatever",
    "102": "whatever",
    "103": "whatever",
]


var output: [String: String] = [:]

for entry in input {
    if let newKey = entry["key"] as? String {
        output[newKey] = "whatever"
    }
}

output

for entry in input {
    let newKey: String = String(entry["key"]!)
    output[newKey] = "whatever"
}

output