fix(frontend-python): support axis as a positional argument for np.expand_dims

frontends/concrete-python/concrete/fhe/tracing/tracer.py

@@ -466,6 +466,10 @@ class Tracer:
             sanitized_args = [self.sanitize(args[0])]
             if len(args) > 1:
                 kwargs["axes"] = args[1]
+        elif func is np.expand_dims:
+            sanitized_args = [self.sanitize(args[0])]
+            if len(args) > 1:
+                kwargs["axis"] = args[1]
         else:
             sanitized_args = [self.sanitize(arg) for arg in args]
 

frontends/concrete-python/tests/execution/test_others.py

@@ -586,6 +586,13 @@ def deterministic_unary_function(x):
             },
             id="fhe.LookupTable(list(range(32)))[x + y]",
         ),
+        pytest.param(
+            lambda x: np.expand_dims(x, 0),
+            {
+                "x": {"status": "encrypted", "range": [-10, 10], "shape": (3, 2)},
+            },
+            id="np.expand_dims(x, 0)",
+        ),
         pytest.param(
             lambda x: np.expand_dims(x, axis=0),
             {