Add Slice function for range type

HyeockJinKim · HyeockJinKim · commit 14646a72be0f · 2019-09-16T02:34:17.000+09:00
Crate a new range object by calculating start, stop, and step when slice is entered as argument to the __getitem__ function of the range Fixes #77
diff --git a/py/range.go b/py/range.go
@@ -79,17 +79,20 @@ func RangeNew(metatype *Type, args Tuple, kwargs StringDict) (Object, error) {
 }
 
 func (r *Range) M__getitem__(key Object) (Object, error) {
+	if slice, ok := key.(*Slice); ok {
+		return computeRangeSlice(r, slice)
+	}
+
 	index, err := Index(key)
 	if err != nil {
 		return nil, err
 	}
-	// TODO(corona10): Support slice case
-	length := computeRangeLength(r.Start, r.Stop, r.Step)
+
 	if index < 0 {
-		index += length
+		index += r.Length
 	}
 
-	if index < 0 || index >= length {
+	if index < 0 || index >= r.Length {
 		return nil, ExceptionNewf(TypeError, "range object index out of range")
 	}
 	result := computeItem(r, index)
@@ -152,6 +155,48 @@ func computeRangeLength(start, stop, step Int) Int {
 	return res
 }
 
+func computeRangeSlice(r *Range, s *Slice) (Object, error) {
+	length, err := r.Length.GoInt()
+	if err != nil {
+		return nil, err
+	}
+	start, stop, step, sliceLength, err := s.GetIndices(length)
+	if err != nil {
+		return nil, err
+	}
+
+	if step == 0 {
+		return nil, ExceptionNewf(ValueError, "slice step cannot be zero")
+	}
+	if start < 0 {
+		start += length
+	}
+	if stop < 0 {
+		stop += length
+	}
+	if start < 0 {
+		start = 0
+	} else if start >= length {
+		start = length
+	}
+	if stop < 0 {
+		stop = 0
+	} else if stop >= length {
+		stop = length
+	}
+
+	startIndex := computeItem(r, Int(start))
+	stopIndex := computeItem(r, Int(stop))
+	stepIndex := Int(step) * r.Step
+
+	return &Range{
+		Start: startIndex,
+		Stop: stopIndex,
+		Step: stepIndex,
+		Length: Int(sliceLength),
+	}, nil
+}
+
 // Check interface is satisfied
 var _ I__getitem__ = (*Range)(nil)
 var _ I__iter__ = (*Range)(nil)
