My original message was referring to someone writing ":" instead of "=" by mistake -- nothing to do with the walrus assignment, but rather using the same notation to assign a value to a key as they would when defining a dict.
OK, I read your Original Post for this thread, about accidentally writing `d["answer"]: 42` instead of `d["answer"] = 42`.
My reaction is that this was a user mistake of the same kind as accidentally writing `x + 1` instead of `x += 1`. That's just going to happen, very occasionally. (Though why? The ':' and '=' keys are not that close together.) Read your code carefully, or in an extreme case step through it in a debugger, and you'll notice the mistake.
It's not a reason to pick on that particular syntax, and not much of a reason to try and introduce a mechanism to disable type hints. Sorry.
PS. This particular syntax was introduced by PEP 526, and introduced in Python 3.6.