Duck Typing

Description

Duck typing determines an object's type based on its behavior, not its explicit type.

In the context of Object Oriented Programming, a protocol is an informal interface, defined only in documentation and not in code. For example, the sequence protocol in Python entails just the len and getitem methods. Any class Spam that implements those methods with the standard signature and semantics can be used anywhere a sequence is expected. Whether Spam is a subclass of this or that is irrelevant, all that matters is that it provides the necessary methods.

Example

The following example shows how the sequence protocol works. SequenceLikeClass implements the sequence protocol by duck typing: to equip with special methods len and getitem, which are methods corresponding to the sequence protocol.

Although it does not inherit from a sequence class like a list, it behaves well like some sequence class.

Another example: