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📘 NAME

typing.Protocol — class Protocol(Generic)

🚀 Quick Reference

Use Case	Command / Code	Description
🏗️ Define a protocol	class Proto(Protocol):	Base class for protocol classes.
🦆 Structural subtyping	class C: def meth(self) -> int: ...	Static duck-typing recognized by type checkers.
✅ Runtime checkable	@typing.runtime_checkable	Simple-minded runtime protocol checking attribute presence.
🧬 Generic protocol	class GenProto(Protocol[T]):	Protocols can be generic over types.

📖 Description

Base class for protocol classes.

Protocol classes are defined as:

class Proto(Protocol):
    def meth(self) -> int:
        ...

Such classes are primarily used with static type checkers that recognize structural subtyping (static duck-typing), for example:

class C:
    def meth(self) -> int:
        return 0

def func(x: Proto) -> int:
    return x.meth()

func(C())  # Passes static type check

See PEP 544 for details. Protocol classes decorated with @typing.runtime_checkable act as simple-minded runtime protocols that check only the presence of given attributes, ignoring their type signatures. Protocol classes can be generic, they are defined as:

class GenProto(Protocol[T]):
    def meth(self) -> T:
        ...

🧬 Method Resolution Order

1. Protocol
2. Generic
3. builtins.object

⚙️ Class Methods Defined Here

• __init_subclass__(*args, **kwargs) from typing._ProtocolMeta
  This method is called when a class is subclassed.
  The default implementation does nothing. It may be overridden to extend subclasses.

🗄️ Data and Other Attributes

• __abstractmethods__ = frozenset()
• __parameters__ = ()

🔗 Class Methods Inherited from Generic

• __class_getitem__(params) from typing._ProtocolMeta

📘 NAME 🚀 Quick Reference 📖 Description 🧬 Method Resolution Order ⚙️ Class Methods Defined Here 🗄️ Data and Other Attributes 🔗 Class Methods Inherited from Generic