Dictionary details

There are a few key points about dictionaries that you should be aware of:

• Sequence operations don't work. As previously stated, dictionaries are mappings, not sequences. Because there's no order to dictionary items, functions such as concatenation and slicing don't work.
• Assigning new indexes adds entries. Keys can be created when making a dictionary (that is, when you initially create the dictionary) or by adding new values to an existing dictionary. The process is similar and the end result is the same.
• Keys can be anything immutable. The previous examples showed keys as string objects, but any non-mutable object (such as numbers) can be used for a key. Numbers can be used to create a list-like object but without the ordering. Tuples are sometimes used to make compound keys; class instances that are designed not to change can also be used if needed.