py: Support __len__ of rangetype.

Author: corona10

py/range.go

@@ -9,10 +9,10 @@ package py
 // A python Range object
 // FIXME one day support BigInts too!
 typeRangestruct{
-StartInt
-StopInt
-StepInt
-//Length Object
+StartInt
+StopInt
+StepInt
+LengthInt
 }
 
 // A python Range iterator
@@ -53,10 +53,12 @@ func RangeNew(metatype *Type, args Tuple, kwargs StringDict) (Object, error){
 returnnil, err
  }
 iflen(args) ==1{
+length:=computeRangeLength(0, startIndex, 1)
 return&Range{
-Start: Int(0),
-Stop: startIndex,
-Step: Int(1),
+Start: Int(0),
+Stop: startIndex,
+Step: Int(1),
+Length: length,
  }, nil
  }
 stopIndex, err:=Index(stop)
@@ -67,10 +69,12 @@ func RangeNew(metatype *Type, args Tuple, kwargs StringDict) (Object, error){
 iferr!=nil{
 returnnil, err
  }
+length:=computeRangeLength(startIndex, stopIndex, stepIndex)
 return&Range{
-Start: startIndex,
-Stop: stopIndex,
-Step: stepIndex,
+Start: startIndex,
+Stop: stopIndex,
+Step: stepIndex,
+Length: length,
  }, nil
 }
 
@@ -82,6 +86,10 @@ func (r *Range) M__iter__() (Object, error){
  }, nil
 }
 
+func (r*Range) M__len__() (Object, error){
+returnr.Length, nil
+}
+
 // Range iterator
 func (it*RangeIterator) M__iter__() (Object, error){
 returnit, nil
@@ -97,6 +105,25 @@ func (it *RangeIterator) M__next__() (Object, error){
 returnr, nil
 }
 
+funccomputeRangeLength(start, stop, stepInt) Int{
+varlo, hiInt
+ifstep>0{
+lo=start
+hi=stop
+step=step
+ } else{
+lo=stop
+hi=start
+step= (-step)
+ }
+
+iflo>=hi{
+returnInt(0)
+ }
+res:= (hi-lo-1)/step+1
+returnres
+}
+
 // Check interface is satisfied
 var_I__iter__= (*Range)(nil)
 var_I_iterator= (*RangeIterator)(nil)

py/tests/range.py

@@ -0,0 +1,16 @@
+# Copyright 2018 The go-python Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+doc="range"
+a=range(255)
+b= [eforeina]
+assertlen(a) ==len(b)
+a=range(5, 100, 5)
+b= [eforeina]
+assertlen(a) ==len(b)
+a=range(100 ,0, 1)
+b= [eforeina]
+assertlen(a) ==len(b)
+
+doc="finished"