From dc1843ea0594251b60a85b08a2616ac3944d7a49 Mon Sep 17 00:00:00 2001
From: Max Jones <14077947+maxrjones@users.noreply.github.com>
Date: Mon, 27 Jul 2026 12:28:48 -0400
Subject: [PATCH 1/3] fix: copy caller-supplied paths instead of aliasing

---
 donfig/config_obj.py        | 10 +++++++---
 donfig/tests/test_config.py | 15 +++++++++++++++
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/donfig/config_obj.py b/donfig/config_obj.py
index 7ae34c4..fcae169 100644
--- a/donfig/config_obj.py
+++ b/donfig/config_obj.py
@@ -399,7 +399,7 @@ def __init__(
         self,
         name: str,
         defaults: Sequence[Mapping[str, Any]] | None = None,
-        paths: list[str] | None = None,
+        paths: Sequence[str] | None = None,
         env: Mapping[str, str] | None = None,
         env_var: str | None = None,
         root_env_var: str | None = None,
@@ -415,7 +415,11 @@ def __init__(
                 *[os.path.join(prefix, "etc", name) for prefix in site.PREFIXES],
                 os.path.join(os.path.expanduser("~"), ".config", name),
             ]
-
+        else:
+            # copy so the env-var append below never mutates the caller's sequence
+            if isinstance(paths, str):
+                raise TypeError("paths must be a sequence of strings, not a single string")
+            paths = list(paths)
         if env_prefix is None:
             env_prefix = f"{name.upper()}_"
         if env is None:
@@ -458,7 +462,7 @@ def __getitem__(self, item):
     def pprint(self, **kwargs):
         return pprint.pprint(self.config, **kwargs)
 
-    def collect(self, paths: list[str] | None = None, env: Mapping[str, str] | None = None) -> dict:
+    def collect(self, paths: Sequence[str] | None = None, env: Mapping[str, str] | None = None) -> dict:
         """Collect configuration from paths and environment variables
 
         Parameters
diff --git a/donfig/tests/test_config.py b/donfig/tests/test_config.py
index c5148bd..2e5254e 100644
--- a/donfig/tests/test_config.py
+++ b/donfig/tests/test_config.py
@@ -606,6 +606,21 @@ def test__get_paths(monkeypatch):
         assert len(paths) == len(set(paths))
 
 
+def test_paths_not_mutated(monkeypatch):
+    monkeypatch.setenv("MYPKG_CONFIG", "foo-bar")
+    paths = ["/etc/mypkg"]
+    config = Config("mypkg", paths=paths)
+    assert config.paths == ["/etc/mypkg", "foo-bar"]
+    # the caller's list is copied on init, not aliased
+    assert paths == ["/etc/mypkg"]
+
+
+def test_paths_accepts_any_sequence(monkeypatch):
+    monkeypatch.setenv("MYPKG_CONFIG", "foo-bar")
+    config = Config("mypkg", paths=("/etc/mypkg",))
+    assert config.paths == ["/etc/mypkg", "foo-bar"]
+
+
 def test_serialization():
     config = Config(CONFIG_NAME)
     config.set(one_key="one_value")

From 2dff88c48e426dc08168db40d8609a8c69b12dbf Mon Sep 17 00:00:00 2001
From: Max Jones <14077947+maxrjones@users.noreply.github.com>
Date: Mon, 27 Jul 2026 17:19:49 -0400
Subject: [PATCH 2/3] refactor: revert type changes

---
 donfig/config_obj.py | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/donfig/config_obj.py b/donfig/config_obj.py
index fcae169..cd19c53 100644
--- a/donfig/config_obj.py
+++ b/donfig/config_obj.py
@@ -399,7 +399,7 @@ def __init__(
         self,
         name: str,
         defaults: Sequence[Mapping[str, Any]] | None = None,
-        paths: Sequence[str] | None = None,
+        paths: list[str] | None = None,
         env: Mapping[str, str] | None = None,
         env_var: str | None = None,
         root_env_var: str | None = None,
@@ -417,8 +417,6 @@ def __init__(
             ]
         else:
             # copy so the env-var append below never mutates the caller's sequence
-            if isinstance(paths, str):
-                raise TypeError("paths must be a sequence of strings, not a single string")
             paths = list(paths)
         if env_prefix is None:
             env_prefix = f"{name.upper()}_"
@@ -462,7 +460,7 @@ def __getitem__(self, item):
     def pprint(self, **kwargs):
         return pprint.pprint(self.config, **kwargs)
 
-    def collect(self, paths: Sequence[str] | None = None, env: Mapping[str, str] | None = None) -> dict:
+    def collect(self, paths: list[str] | None = None, env: Mapping[str, str] | None = None) -> dict:
         """Collect configuration from paths and environment variables
 
         Parameters

From ccf0e9e5fe3934b10de6fd0980aa53a4ca916ace Mon Sep 17 00:00:00 2001
From: Max Jones <14077947+maxrjones@users.noreply.github.com>
Date: Mon, 27 Jul 2026 17:21:15 -0400
Subject: [PATCH 3/3] Update paths

---
 donfig/config_obj.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/donfig/config_obj.py b/donfig/config_obj.py
index cd19c53..738ac7f 100644
--- a/donfig/config_obj.py
+++ b/donfig/config_obj.py
@@ -416,7 +416,7 @@ def __init__(
                 os.path.join(os.path.expanduser("~"), ".config", name),
             ]
         else:
-            # copy so the env-var append below never mutates the caller's sequence
+            # copy so the env-var append below never mutates the caller's list
             paths = list(paths)
         if env_prefix is None:
             env_prefix = f"{name.upper()}_"