py: Fix __mul__ of list and tuple on negative case (#67)

Author: corona10

py/list.go

@@ -259,6 +259,9 @@ func (l *List) M__mul__(other Object) (Object, error) {
 	if b, ok := convertToInt(other); ok {
 		m := len(l.Items)
 		n := int(b) * m
+		if n < 0 {
+			n = 0
+		}
 		newList := NewListSized(n)
 		for i := 0; i < n; i += m {
 			copy(newList.Items[i:i+m], l.Items)

py/tests/list.py

@@ -33,4 +33,10 @@
 assert repr(a) == "['a', 'b', 'c', 'd', 'e', 'f']"
 assertRaises(TypeError, lambda: [].append())
 
+doc="mul"
+a = [1, 2, 3]
+assert a * 2  == [1, 2, 3, 1, 2, 3]
+assert a * 0 == []
+assert a * -1 == []
+
 doc="finished"

py/tests/tuple.py

@@ -14,4 +14,10 @@
 assert repr((1,(2,3),4)) == "(1, (2, 3), 4)"
 assert repr(("1",(2.5,17,()))) == "('1', (2.5, 17, ()))"
 
+doc="mul"
+a = (1, 2, 3)
+assert a * 2  == (1, 2, 3, 1, 2, 3)
+assert a * 0 == ()
+assert a * -1 == ()
+
 doc="finished"

py/tuple.go

@@ -113,6 +113,7 @@ func (a Tuple) M__add__(other Object) (Object, error) {
 		copy(newTuple[len(b):], b)
 		return newTuple, nil
 	}
+
 	return NotImplemented, nil
 }
 
@@ -131,6 +132,9 @@ func (l Tuple) M__mul__(other Object) (Object, error) {
 	if b, ok := convertToInt(other); ok {
 		m := len(l)
 		n := int(b) * m
+		if n < 0 {
+			n = 0
+		}
 		newTuple := make(Tuple, n)
 		for i := 0; i < n; i += m {
 			copy(newTuple[i:i+m], l)