Merge pull request numba#7848 from njriasan/nick/int_list_mul

Support for int * list

numba/core/typing/listdecl.py

@@ -153,6 +153,8 @@ def generic(self, args, kws):
         a, b = args
         if isinstance(a, types.List) and isinstance(b, types.Integer):
             return signature(a, a, types.intp)
+        elif isinstance(a, types.Integer) and isinstance(b, types.List):
+            return signature(b, types.intp, b)
 
 
 @infer_global(operator.imul)

numba/cpython/listobj.py

@@ -714,11 +714,16 @@ def list_add_inplace(context, builder, sig, args):
 
 
 @lower_builtin(operator.mul, types.List, types.Integer)
+@lower_builtin(operator.mul, types.Integer, types.List)
 def list_mul(context, builder, sig, args):
-    src = ListInstance(context, builder, sig.args[0], args[0])
+    if isinstance(sig.args[0], types.List):
+        list_idx, int_idx = 0, 1
+    else:
+        list_idx, int_idx = 1, 0
+    src = ListInstance(context, builder, sig.args[list_idx], args[list_idx])
     src_size = src.size
 
-    mult = args[1]
+    mult = args[int_idx]
     zero = ir.Constant(mult.type, 0)
     mult = builder.select(cgutils.is_neg_int(builder, mult), zero, mult)
     nitems = builder.mul(mult, src_size)

numba/tests/test_lists.py

@@ -312,6 +312,10 @@ def list_mul(n, v):
     a = list(range(n))
     return a * v
 
+def list_mul2(n, v):
+    a = list(range(n))
+    return v * a
+
 def list_mul_inplace(n, v):
     a = list(range(n))
     a *= v
@@ -656,6 +660,9 @@ def check_mul(self, pyfunc):
     def test_mul(self):
         self.check_mul(list_mul)
 
+    def test_mul2(self):
+        self.check_mul(list_mul2)
+
     def test_mul_inplace(self):
         self.check_mul(list_mul_inplace)