A dictionary display is a possibly empty series of key/datum pairs
enclosed in curly braces:
dict_display: "{" [key_datum_list] "}"
key_datum_list: key_datum ("," key_datum)* [","]
key_datum: condition ":" condition
A dictionary display yields a new dictionary object.
The key/datum pairs are evaluated from left to right to define the entries of the dictionary: each key object is used as a key into the dictionary to store the corresponding datum.
Restrictions on the types of the key values are listed earlier in
section 
.
Clashes between duplicate keys are not detected; the last
datum (textually rightmost in the display) stored for a given key
value prevails.