Unable to merge MutableHeaders with dict

[manlix]

Checklist

• The bug is reproducible against the latest release and/or master.
• There are no similar issues or pull requests to fix it yet.

Describe the bug

Unable to merge MutableHeaders with dict.

To reproduce

from starlette.datastructures import MutableHeaders

response = MutableHeaders()
response |= {"X-Header": "string"}

Expected behavior

>>> response
MutableHeaders({'x-header': 'string'})

Actual behavior

Raised exception:

TypeError: unsupported operand type(s) for |=: 'MutableHeaders' and 'dict'

Environment

• OS: Ubuntu 21.04
• Python version: 3.9.6
• Starlette version: 0.15.0

Additional context

Method MutableHeaders.update() can resolve the issue but I think comfortable is used to operators | (for merge) and |= (for update).

It's comfortable if you have many headers like:

...

headers = {
    "X-Header-1": "string-1",
    "X-Header-1": "string-2",
    "X-Header-3": "string-3",
    "X-Header-...": "string-...",
    "X-Header-N": "string-N",
}

response.headers |= headers  # equals to: response.headers.update(headers)

return response

...

It's like Dictionary Merge & Update Operators in Python 3.9.

What do you think about it? Thank you.

[graingert]

imho this is a cPython bug. _collections_abc.Mapping should define these mixin methods

[Kludex]

Based on PEP-584, it does look like a CPython bug 🤔

EDIT: I've read it again, and is not a bug on CPython. It's as intended.