From 60110c257b4871c84d983c6b34bd754623b619b9 Mon Sep 17 00:00:00 2001
From: Matthew Newville <newville@cars.uchicago.edu>
Date: Sun, 15 Dec 2024 15:42:06 -0600
Subject: [PATCH 1/3] add basic test for model function with barestar to
 indicate keyword-only arguments

---
 tests/test_model.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tests/test_model.py b/tests/test_model.py
index 7f4bbdfb..368496e1 100644
--- a/tests/test_model.py
+++ b/tests/test_model.py
@@ -1697,3 +1697,16 @@ def test_model_refitting():
     assert result.init_values['peak_amplitude'] < 21
     assert result.init_values['peak_sigma'] > 2
     assert result.init_values['peak_sigma'] < 4
+
+
+def test_model_barestar():
+    """Github #976 (and discussion #975)"""
+    def foo(x, *, a=1, b=1, kind='linear'):
+        if kind == 'linear':
+            return a + b * x
+        elif kind == 'exponential':
+            return a * np.exp(b * x)
+
+    modl = lmfit.Model(foo)
+    assert modl.independent_vars == ['x', 'kind']
+    assert modl._param_names == ['a', 'b']

From 085fe1c68f2280ff6103588bd6da8dfff564a3f8 Mon Sep 17 00:00:00 2001
From: Matthew Newville <newville@cars.uchicago.edu>
Date: Sun, 15 Dec 2024 15:43:34 -0600
Subject: [PATCH 2/3] add support for "bare star" and keyword-only arguments in
 model function signatures

---
 lmfit/model.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lmfit/model.py b/lmfit/model.py
index 34a78c78..289da872 100644
--- a/lmfit/model.py
+++ b/lmfit/model.py
@@ -529,16 +529,20 @@ def _parse_params(self):
             for fnam, fpar in sig.parameters.items():
                 if fpar.kind == fpar.VAR_KEYWORD:
                     keywords_ = fnam
-                elif fpar.kind in (fpar.POSITIONAL_ONLY, fpar.POSITIONAL_OR_KEYWORD):
+                elif fpar.kind in (fpar.KEYWORD_ONLY,
+                                   fpar.POSITIONAL_OR_KEYWORD):
                     default_vals[fnam] = fpar.default
                     if (isinstance(fpar.default, (float, int, complex))
                        and not isinstance(fpar.default, bool)):
                         kw_args[fnam] = fpar.default
+                        pos_args.append(fnam)
                     elif fpar.default == fpar.empty:
                         pos_args.append(fnam)
                     else:
                         kw_args[fnam] = fpar.default
                         indep_vars.append(fnam)
+                elif fpar.kind == fpar.POSITIONAL_ONLY:
+                    raise ValueError("positional only arguments with '/' are not supported")
                 elif fpar.kind == fpar.VAR_POSITIONAL:
                     raise ValueError(f"varargs '*{fnam}' is not supported")
         # inspection done

From 200b069869a8c9178b2d57f04d6317127e0eb972 Mon Sep 17 00:00:00 2001
From: Matthew Newville <newville@cars.uchicago.edu>
Date: Sun, 15 Dec 2024 16:15:33 -0600
Subject: [PATCH 3/3] add test for bareslash, asserting ValueError

---
 tests/test_model.py | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/tests/test_model.py b/tests/test_model.py
index 368496e1..a77b94a6 100644
--- a/tests/test_model.py
+++ b/tests/test_model.py
@@ -1710,3 +1710,19 @@ def foo(x, *, a=1, b=1, kind='linear'):
     modl = lmfit.Model(foo)
     assert modl.independent_vars == ['x', 'kind']
     assert modl._param_names == ['a', 'b']
+
+
+def test_model_bareslash():
+    """Github #976 (and discussion #975)"""
+    def foo(x, /, a=1, b=1, kind='linear'):
+        if kind == 'linear':
+            return a + b * x
+        elif kind == 'exponential':
+            return a * np.exp(b * x)
+    try:
+        lmfit.Model(foo)
+        that_failed = False
+    except ValueError:
+        that_failed = True
+
+    assert that_failed