deduplicate querystring using a pre-made url

stripe/_api_requestor.py

@@ -556,6 +556,28 @@ def _args_for_request_with_retries(
             url,
         )
 
+        params = params or {}
+        if params and (method == "get" or method == "delete"):
+            # if we're sending params in the querystring, then we have to make sure we're not
+            # duplicating anything we got back from the server already (like in a list iterator)
+            # so, we parse the querystring the server sends back so we can merge with what we (or the user) are trying to send
+            # note: server sends back "expand[]" but users supply "expand", so we have to match them up
+            existing_params = {
+                "expand" if k == "expand[]" else k: v
+                for k, v in parse_qs(urlsplit(url).query).items()
+            }
+            # if a user is expanding something that wasn't expanded before, add (and deduplicate) it
+            if "expand" in existing_params and "expand" in params:
+                params["expand"] = list(  # type:ignore - this is a dict
+                    set([*existing_params["expand"], *params["expand"]])
+                )
+
+            params = {
+                **existing_params,
+                # user_supplied params take precedence over server params
+                **params,
+            }
+
         encoded_params = urlencode(list(_api_encode(params or {}, api_mode)))
 
         # Don't use strict form encoding by changing the square bracket control
@@ -586,13 +608,13 @@ def _args_for_request_with_retries(
 
         if method == "get" or method == "delete":
             if params:
-                query = encoded_params
-                scheme, netloc, path, base_query, fragment = urlsplit(abs_url)
+                # if we're sending query params, we've already merged the incoming ones with the server's "url"
+                # so we can overwrite the whole thing
+                scheme, netloc, path, _, fragment = urlsplit(abs_url)
 
-                if base_query:
-                    query = "%s&%s" % (base_query, query)
-
-                abs_url = urlunsplit((scheme, netloc, path, query, fragment))
+                abs_url = urlunsplit(
+                    (scheme, netloc, path, encoded_params, fragment)
+                )
             post_data = None
         elif method == "post":
             if (

tests/api_resources/test_list_object.py

@@ -3,6 +3,7 @@
 import pytest
 
 import stripe
+from tests.http_client_mock import HTTPClientMock
 
 
 class TestListObject(object):
@@ -439,6 +440,58 @@ def test_forwards_api_key_to_nested_resources(self, http_client_mock):
         )
         assert lo.data[0].api_key == "sk_test_iter_forwards_options"
 
+    def test_iter_with_params(self, http_client_mock: HTTPClientMock):
+        http_client_mock.stub_request(
+            "get",
+            path="/v1/invoices/upcoming/lines",
+            query_string="customer=cus_123&expand[0]=data.price&limit=1",
+            rbody=json.dumps(
+                {
+                    "object": "list",
+                    "data": [
+                        {
+                            "id": "prod_001",
+                            "object": "product",
+                            "price": {"object": "price", "id": "price_123"},
+                        }
+                    ],
+                    "url": "/v1/invoices/upcoming/lines?customer=cus_123&expand%5B%5D=data.price",
+                    "has_more": True,
+                }
+            ),
+        )
+        # second page
+        http_client_mock.stub_request(
+            "get",
+            path="/v1/invoices/upcoming/lines",
+            query_string="customer=cus_123&expand[0]=data.price&limit=1&starting_after=prod_001",
+            rbody=json.dumps(
+                {
+                    "object": "list",
+                    "data": [
+                        {
+                            "id": "prod_002",
+                            "object": "product",
+                            "price": {"object": "price", "id": "price_123"},
+                        }
+                    ],
+                    "url": "/v1/invoices/upcoming/lines?customer=cus_123&expand%5B%5D=data.price",
+                    "has_more": False,
+                }
+            ),
+        )
+
+        lo = stripe.Invoice.upcoming_lines(
+            api_key="sk_test_invoice_lines",
+            customer="cus_123",
+            expand=["data.price"],
+            limit=1,
+        )
+
+        seen = [item["id"] for item in lo.auto_paging_iter()]
+
+        assert seen == ["prod_001", "prod_002"]
+
 
 class TestAutoPagingAsync:
     @staticmethod