Add support for the abs builtin (#28)

Implement the `abs` as defined here:

* https://docs.python.org/2.7/library/functions.html#abs

runtime/builtin_types.go

@@ -183,6 +183,13 @@ func initBuiltinType(typ *Type, info *builtinTypeInfo) {
 	}
 }
 
+func builtinAbs(f *Frame, args Args, _ KWArgs) (*Object, *BaseException) {
+	if raised := checkFunctionArgs(f, "abs", args, ObjectType); raised != nil {
+		return nil, raised
+	}
+	return Abs(f, args[0])
+}
+
 func builtinBin(f *Frame, args Args, _ KWArgs) (*Object, *BaseException) {
 	if raised := checkFunctionArgs(f, "bin", args, ObjectType); raised != nil {
 		return nil, raised
@@ -464,6 +471,7 @@ func builtinUniChr(f *Frame, args Args, _ KWArgs) (*Object, *BaseException) {
 func init() {
 	builtinMap := map[string]*Object{
 		"__frame__":      newBuiltinFunction("__frame__", builtinFrame).ToObject(),
+		"abs":            newBuiltinFunction("abs", builtinAbs).ToObject(),
 		"bin":            newBuiltinFunction("bin", builtinBin).ToObject(),
 		"chr":            newBuiltinFunction("chr", builtinChr).ToObject(),
 		"dir":            newBuiltinFunction("dir", builtinDir).ToObject(),

runtime/builtin_types_test.go

@@ -56,6 +56,15 @@ func TestBuiltinFuncs(t *testing.T) {
 		want    *Object
 		wantExc *BaseException
 	}{
+		{f: "abs", args: wrapArgs(1, 2, 3), wantExc: mustCreateException(TypeErrorType, "'abs' requires 1 arguments")},
+		{f: "abs", args: wrapArgs(1), want: NewInt(1).ToObject()},
+		{f: "abs", args: wrapArgs(-1), want: NewInt(1).ToObject()},
+		{f: "abs", args: wrapArgs(big.NewInt(2)), want: NewLong(big.NewInt(2)).ToObject()},
+		{f: "abs", args: wrapArgs(big.NewInt(-2)), want: NewLong(big.NewInt(2)).ToObject()},
+		{f: "abs", args: wrapArgs(NewFloat(3.4)), want: NewFloat(3.4).ToObject()},
+		{f: "abs", args: wrapArgs(NewFloat(-3.4)), want: NewFloat(3.4).ToObject()},
+		{f: "abs", args: wrapArgs(MinInt), want: NewLong(big.NewInt(MinInt).Neg(minIntBig)).ToObject()},
+		{f: "abs", args: wrapArgs(NewStr("a")), wantExc: mustCreateException(TypeErrorType, "bad operand type for abs(): 'str'")},
 		{f: "bin", args: wrapArgs(64 + 8 + 1), want: NewStr("0b1001001").ToObject()},
 		{f: "bin", args: wrapArgs(MinInt), want: NewStr(fmt.Sprintf("-0b%b0", -(MinInt >> 1))).ToObject()},
 		{f: "bin", args: wrapArgs(0), want: NewStr("0b0").ToObject()},

runtime/core.go

@@ -23,6 +23,16 @@ import (
 
 var logFatal = func(msg string) { log.Fatal(msg) }
 
+// Abs returns the result of o.__abs__ and is equivalent to the Python
+// expression "abs(o)".
+func Abs(f *Frame, o *Object) (*Object, *BaseException) {
+	abs := o.typ.slots.Abs
+	if abs == nil {
+		return nil, f.RaiseType(TypeErrorType, fmt.Sprintf("bad operand type for abs(): '%s'", o.typ.Name()))
+	}
+	return abs.Fn(f, o)
+}
+
 // Add returns the result of adding v and w together according to the
 // __add/radd__ operator.
 func Add(f *Frame, v, w *Object) (*Object, *BaseException) {

runtime/float.go

@@ -50,6 +50,11 @@ func (f *Float) Value() float64 {
 	return f.value
 }
 
+func floatAbs(f *Frame, o *Object) (*Object, *BaseException) {
+	z := toFloatUnsafe(o).Value()
+	return NewFloat(math.Abs(z)).ToObject(), nil
+}
+
 func floatAdd(f *Frame, v, w *Object) (*Object, *BaseException) {
 	return floatArithmeticOp(f, "__add__", v, w, func(v, w float64) float64 { return v + w })
 }
@@ -221,6 +226,7 @@ func floatSub(f *Frame, v, w *Object) (*Object, *BaseException) {
 
 func initFloatType(dict map[string]*Object) {
 	dict["__getnewargs__"] = newBuiltinFunction("__getnewargs__", floatGetNewArgs).ToObject()
+	FloatType.slots.Abs = &unaryOpSlot{floatAbs}
 	FloatType.slots.Add = &binaryOpSlot{floatAdd}
 	FloatType.slots.Div = &binaryOpSlot{floatDiv}
 	FloatType.slots.Eq = &binaryOpSlot{floatEq}

runtime/int.go

@@ -66,6 +66,18 @@ func (i *Int) IsTrue() bool {
 // IntType is the object representing the Python 'int' type.
 var IntType = newBasisType("int", reflect.TypeOf(Int{}), toIntUnsafe, ObjectType)
 
+func intAbs(f *Frame, o *Object) (*Object, *BaseException) {
+	z := toIntUnsafe(o)
+	if z.Value() > 0 {
+		return z.ToObject(), nil
+	}
+	if z.Value() == MinInt {
+		nz := big.NewInt(int64(z.Value()))
+		return NewLong(nz.Neg(nz)).ToObject(), nil
+	}
+	return NewInt(-z.Value()).ToObject(), nil
+}
+
 func intAdd(f *Frame, v, w *Object) (*Object, *BaseException) {
 	return intAddMulOp(f, "__add__", v, w, intCheckedAdd, longAdd)
 }
@@ -287,6 +299,7 @@ func intXor(f *Frame, v, w *Object) (*Object, *BaseException) {
 
 func initIntType(dict map[string]*Object) {
 	dict["__getnewargs__"] = newBuiltinFunction("__getnewargs__", intGetNewArgs).ToObject()
+	IntType.slots.Abs = &unaryOpSlot{intAbs}
 	IntType.slots.Add = &binaryOpSlot{intAdd}
 	IntType.slots.And = &binaryOpSlot{intAnd}
 	IntType.slots.Div = &binaryOpSlot{intDiv}

runtime/long.go

@@ -86,6 +86,10 @@ func (l *Long) Neg() *Long {
 // LongType is the object representing the Python 'long' type.
 var LongType = newBasisType("long", reflect.TypeOf(Long{}), toLongUnsafe, ObjectType)
 
+func longAbs(z, x *big.Int) {
+	z.Abs(x)
+}
+
 func longAdd(z, x, y *big.Int) {
 	z.Add(x, y)
 }
@@ -299,6 +303,7 @@ func longXor(z, x, y *big.Int) {
 
 func initLongType(dict map[string]*Object) {
 	dict["__getnewargs__"] = newBuiltinFunction("__getnewargs__", longGetNewArgs).ToObject()
+	LongType.slots.Abs = longUnaryOpSlot(longAbs)
 	LongType.slots.Add = longBinaryOpSlot(longAdd)
 	LongType.slots.And = longBinaryOpSlot(longAnd)
 	LongType.slots.Div = longDivModOpSlot(longDiv)

runtime/slots.go

@@ -369,6 +369,7 @@ func (s *unaryOpSlot) wrapCallable(callable *Object) bool {
 // The wrapper structs permit comparison of like slots which is occasionally
 // necessary to determine whether a function has been overridden by a subclass.
 type typeSlots struct {
+	Abs          *unaryOpSlot
 	Add          *binaryOpSlot
 	And          *binaryOpSlot
 	Basis        *basisSlot

testing/builtin_test.py

@@ -0,0 +1,36 @@
+# Copyright 2016 Google Inc. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# pylint: disable=g-equals-none
+
+# abs(x)
+
+assert abs(1) == 1
+assert abs(-1) == 1
+assert isinstance(abs(-1), int)
+
+assert abs(long(2)) == 2
+assert abs(long(-2)) == 2
+assert isinstance(abs(long(-2)), long)
+
+assert abs(3.4) == 3.4
+assert abs(-3.4) == 3.4
+assert isinstance(abs(-3.4), float)
+
+try:
+  abs('a')
+except TypeError as e:
+  assert str(e) == "bad operand type for abs(): 'str'"
+else:
+  raise AssertionError('this was supposed to raise an exception')