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Add Slice function for range type #83

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Merged
merged 3 commits into from
Sep 26, 2019
Merged

Add Slice function for range type #83

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0203481
Add Slice function for range type
HyeockJinKim Sep 25, 2019
bedc71c
Add typecall for __index__ in Index function
HyeockJinKim Sep 26, 2019
2da2efa
Add tests for range
HyeockJinKim Sep 26, 2019
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Add Slice function for range type 
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
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@HyeockJinKim
HyeockJinKim committed Sep 25, 2019
commit 0203481f3655b21918e901ce518084f1df754519
77 changes: 70 additions & 7 deletions py/range.go
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Original file line number Diff line number Diff line change
Expand Up @@ -79,18 +79,18 @@ 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 = computeNegativeIndex(index, r.Length)

if index < 0 || index >= length {
return nil, ExceptionNewf(TypeError, "range object index out of range")
if index < 0 || index >= r.Length {
return nil, ExceptionNewf(IndexError, "range object index out of range")
}
result := computeItem(r, index)
return result, nil
Expand Down Expand Up @@ -160,6 +160,69 @@ func computeRangeLength(start, stop, step Int) Int {
return res
}

func computeNegativeIndex(index, length Int) Int {
if index < 0 {
index += length
}
return index
}

func computeBoundIndex(index, length Int) Int {
if index < 0 {
index = 0
} else if index > length {
index = length
}
return index
}

func computeRangeSlice(r *Range, s *Slice) (Object, error) {
start, err := Index(s.Start)
if err != nil {
start = 0
}
stop, err := Index(s.Stop)
if err != nil {
stop = r.Length
}

step, err := Index(s.Step)
if err != nil {
step = 1
}
if step == 0 {
return nil, ExceptionNewf(ValueError, "slice step cannot be zero")
}
start = computeNegativeIndex(start, r.Length)
stop = computeNegativeIndex(stop, r.Length)

start = computeBoundIndex(start, r.Length)
stop = computeBoundIndex(stop, r.Length)

startIndex := computeItem(r, start)
stopIndex := computeItem(r, stop)
stepIndex := step * r.Step

var sliceLength Int
if start < stop {
if stepIndex < 0 {
startIndex, stopIndex = stopIndex-1, startIndex-1
}
} else {
if stepIndex < 0 {
startIndex, stopIndex = stopIndex+1, startIndex+1
}
}
sliceLength = computeRangeLength(startIndex, stopIndex, stepIndex)

return &Range{
Start: startIndex,
Stop: stopIndex,
Step: stepIndex,
Length: sliceLength,
}, nil
}

// Check interface is satisfied
var _ I__getitem__ = (*Range)(nil)
var _ I__iter__ = (*Range)(nil)
Expand Down