While par's answer is essentially the right response there are still a few subtle issues:
A "dictionary type" is an abstract data type. An instance (basically an element) of that type is literally a function like the one par describes. But the "dictionary type" comes with a bunch of operations that you are allowed to do with its members, for example:
- adding a pair $(k, v)$ to the dictionary
- removing a pair $(k,v)$ from the dictionary
- changing the value $v$ that the key $k$ is mapped to
- finding the value $v$ that the key $k$ is mapped to
and possible more or less (depending on your definition). These operations are part of the definition of an abstract data type. Pure mathematics often does not concern itself directly with computability or how fast something can be computed, but (theoretical) computer science does.
Any abstracted data type may be implemented by numerous different data structures, which differ in the algorithms they use to execute these operations, how the data is stored etc. . None of this (directly) matters for abstract mathematical "function".
Another thing to keep in mind is that members of a type in a programming language are commonly mutable, i.e. they can be "changed over time". This is a feature that we don't normally have in pure mathematics, things do not change over time. There are multiple ways to deal with that: One is insisting that the dictionary has to be immutable and that the operations yield new dictionaries. Another way is thinking of a dictionary as a sequence of functions, where the values of that sequence are certain instances of the dictionary through time.
A more sophisticated method uses a different kind of logic (other than predicate logic) for example temporal logic.
One last issue: I completely ignored any other side effects like exceptions that the Python dictionary may throw. I hear this can be modeled by (computer-scientific) monads.