Consider this contrived example;
@dataclass
class A:
name: str = "John"
....
@dataclass
class B:
name: str = "Doe"
Q: How do I type hint an object that has an attribute, such as the following?
def print_name(obj: HasAttr['name'])
print(obj.name)
I understand the SO rule on showing what you have tried. The best I can offer is that I've searched the docs; Pep526, PythonSheets, Docs, and am aware of this SO Question. None seem to help (or maybe I missed it.)
[Edit] I recognize that you can get there with inheritance, but I don't want to go that route.
So, what you are describing is structural typing. This is distinct from the class-based nominal subtyping that the python typing system is based on. However, structural subtyping is sort of the statically typed version of Python's dynamic duck typing.
Python's typing system allows a form of this through typing.Protocol
.
An example, suppose we have a Python module, test_typing.py
:
from typing import Protocol
from dataclasses import dataclass
class Named(Protocol):
name: str
@dataclass
class A:
name: str
id: int
@dataclass
class B:
name: int
@dataclass
class C:
foo: str
def frobnicate(obj: Named) -> int:
return sum(map(ord, obj.name))
frobnicate(A('Juan', 1))
frobnicate(B(8))
frobnicate(C('Jon'))
Using mypy version 0.790:
(py38) juanarrivillaga@Juan-Arrivillaga-MacBook-Pro ~ % mypy test_typing.py
test_typing.py:28: error: Argument 1 to "frobnicate" has incompatible type "B"; expected "Named"
test_typing.py:28: note: Following member(s) of "B" have conflicts:
test_typing.py:28: note: name: expected "str", got "int"
test_typing.py:29: error: Argument 1 to "frobnicate" has incompatible type "C"; expected "Named"
Found 2 errors in 1 file (checked 1 source file)