fix: register QueryParams as Mapping for isinstance check

python/httpx/_urls.py

@@ -12,6 +12,12 @@ from ._urlparse import urlparse
 __all__ = ["URL", "QueryParams"]
 
 
+if not typing.TYPE_CHECKING:
+    from collections.abc import Mapping
+
+    Mapping.register(QueryParams)
+
+
 class URL:
     """
     url = httpx.URL("HTTPS://jo%40email.com:a%20secret@müller.de:1234/pa%20th?search=ab#anchorlink")

tests/client/test_queryparams.py

@@ -1,3 +1,5 @@
+import typing
+
 import httpx
 
 
@@ -5,6 +7,13 @@ def hello_world(request: httpx.Request) -> httpx.Response:
     return httpx.Response(200, text="Hello, world")
 
 
+def test_queryparams_isinstance_of_mapping():
+    client = httpx.Client(params={"a": "b"})
+    assert isinstance(client.params, httpx.QueryParams)
+    assert isinstance(client.params, typing.Mapping)
+    assert client.params["a"] == "b"
+
+
 def test_client_queryparams():
     client = httpx.Client(params={"a": "b"})
     assert isinstance(client.params, httpx.QueryParams)