You can get values by key, but you can't get keys by value. You can not have duplicate keys in a dictionary. Assigning a value to an existing key will wipe out the old value. You can add new key-value pairs at any time. This syntax is identical to modifying existing values.
Dictionaries have no concept of order among elements.
There are ways of doing this, they're just not built into the dictionary. Dictionary values can be any datatype, including strings, integers, objects, or even other dictionaries. You can also mix and match key datatypes within a dictionary. Note that the set of empty curly braces signifies a dictionary with no items. Assigning a value to an existing dictionary key simply replaces the old value with a new one.