Provide hook to implement __repr__ (#808)

Provide hook to implement __repr__

AUTHORS.md

@@ -41,6 +41,7 @@
 -   Luke Stratman ([@lstratman](https://github.com/lstratman))
 -   Konstantin Posudevskiy ([@konstantin-posudevskiy](https://github.com/konstantin-posudevskiy))
 -   Matthias Dittrich ([@matthid](https://github.com/matthid))
+-   Mohamed Koubaa ([@koubaa](https://github.com/koubaa))
 -   Patrick Stewart ([@patstew](https://github.com/patstew))
 -   Raphael Nestler ([@rnestler](https://github.com/rnestler))
 -   Rickard Holmberg ([@rickardraysearch](https://github.com/rickardraysearch))

CHANGELOG.md

@@ -46,6 +46,7 @@ This document follows the conventions laid out in [Keep a CHANGELOG][].
 -   Added PyObject finalizer support, Python objects referred by C# can be auto collect now ([#692][p692]).
 -   Added detailed comments about aproaches and dangers to handle multi-app-domains ([#625][p625])
 -   Python 3.7 support, builds and testing added. Defaults changed from Python 3.6 to 3.7 ([#698][p698])
+-   Added support for C# types to provide `__repr__` ([#680][p680])
 
 ### Changed
 

src/runtime/classbase.cs

@@ -246,6 +246,44 @@ namespace Python.Runtime
             }
         }
 
+        public static IntPtr tp_repr(IntPtr ob)
+        {
+            var co = GetManagedObject(ob) as CLRObject;
+            if (co == null)
+            {
+                return Exceptions.RaiseTypeError("invalid object");
+            }
+            try
+            {
+                //if __repr__ is defined, use it
+                var instType = co.inst.GetType();
+                System.Reflection.MethodInfo methodInfo = instType.GetMethod("__repr__");
+                if (methodInfo != null && methodInfo.IsPublic)
+                {
+                    var reprString = methodInfo.Invoke(co.inst, null) as string;
+                    return Runtime.PyString_FromString(reprString);
+                }
+
+                //otherwise use the standard object.__repr__(inst)
+                IntPtr args = Runtime.PyTuple_New(1);
+                Runtime.PyTuple_SetItem(args, 0, ob);
+                IntPtr reprFunc = Runtime.PyObject_GetAttrString(Runtime.PyBaseObjectType, "__repr__");
+                var output =  Runtime.PyObject_Call(reprFunc, args, IntPtr.Zero);
+                Runtime.XDecref(args);
+                Runtime.XDecref(reprFunc);
+                return output;
+            }
+            catch (Exception e)
+            {
+                if (e.InnerException != null)
+                {
+                    e = e.InnerException;
+                }
+                Exceptions.SetError(e);
+                return IntPtr.Zero;
+            }
+        }
+
 
         /// <summary>
         /// Standard dealloc implementation for instances of reflected types.

src/runtime/exceptions.cs

@@ -36,6 +36,29 @@ namespace Python.Runtime
             return e;
         }
 
+        /// <summary>
+        /// Exception __repr__ implementation
+        /// </summary>
+        public new static IntPtr tp_repr(IntPtr ob)
+        {
+            Exception e = ToException(ob);
+            if (e == null)
+            {
+                return Exceptions.RaiseTypeError("invalid object");
+            }
+            string name = e.GetType().Name;
+            string message;
+            if (e.Message != String.Empty)
+            {
+                message = String.Format("{0}('{1}')", name, e.Message);
+            }
+            else
+            {
+                message = String.Format("{0}()", name);
+            }
+            return Runtime.PyUnicode_FromString(message);
+        }
+
         /// <summary>
         /// Exception __str__ implementation
         /// </summary>

src/testing/Python.Test.csproj

@@ -91,6 +91,7 @@
     <Compile Include="threadtest.cs" />
     <Compile Include="doctest.cs" />
     <Compile Include="subclasstest.cs" />
+    <Compile Include="ReprTest.cs" />
   </ItemGroup>
   <ItemGroup>
     <Reference Include="Microsoft.CSharp" />
@@ -111,4 +112,4 @@
     <Copy SourceFiles="$(TargetAssembly)" DestinationFolder="$(SolutionDir)\src\tests\fixtures" />
     <!--Copy SourceFiles="$(TargetAssemblyPdb)" Condition="Exists('$(TargetAssemblyPdb)')" DestinationFolder="$(PythonBuildDir)" /-->
   </Target>
-</Project>
+</Project>

src/testing/ReprTest.cs

@@ -0,0 +1,108 @@
+using System;
+using System.Text;
+
+namespace Python.Test
+{
+    /// <summary>
+    /// Supports repr unit tests.
+    /// </summary>
+    public class ReprTest
+    {
+        public class Point
+        {
+            public Point(double x, double y)
+            {
+                X = x;
+                Y = y;
+            }
+
+            public double X { get; set; }
+            public double Y { get; set; }
+
+            public override string ToString()
+            {
+                return base.ToString() + ": X=" + X.ToString() + ", Y=" + Y.ToString();
+            }
+
+            public string __repr__()
+            {
+                return "Point(" + X.ToString() + "," + Y.ToString() + ")";
+            }
+        }
+
+        public class Foo
+        {
+            public string __repr__()
+            {
+                return "I implement __repr__() but not ToString()!";
+            }
+        }
+
+        public class Bar
+        {
+            public override string ToString()
+            {
+                return "I implement ToString() but not __repr__()!";
+            }
+        }
+
+        public class BazBase
+        {
+            public override string ToString()
+            {
+                return "Base class implementing ToString()!";
+            }
+        }
+
+        public class BazMiddle : BazBase
+        {
+            public override string ToString()
+            {
+                return "Middle class implementing ToString()!";
+            }
+        }
+
+        //implements ToString via BazMiddle
+        public class Baz : BazMiddle
+        {
+
+        }
+
+        public class Quux
+        {
+            public string ToString(string format)
+            {
+                return "I implement ToString() with an argument!";
+            }
+        }
+
+        public class QuuzBase
+        {
+            protected string __repr__()
+            {
+                return "I implement __repr__ but it isn't public!";
+            }
+        }
+
+        public class Quuz : QuuzBase
+        {
+
+        }
+
+        public class Corge
+        {
+            public string __repr__(int i)
+            {
+                return "__repr__ implemention with input parameter!";
+            }
+        }
+
+        public class Grault
+        {
+            public int __repr__()
+            {
+                return "__repr__ implemention with wrong return type!".Length;
+            }
+        }
+    }
+}

src/tests/test_exceptions.py

@@ -282,11 +282,8 @@ def test_python_compat_of_managed_exceptions():
 
     assert e.args == (msg,)
     assert isinstance(e.args, tuple)
-    if PY3:
-        strexp = "OverflowException('Simple message"
-        assert repr(e)[:len(strexp)] == strexp
-    elif PY2:
-        assert repr(e) == "OverflowException(u'Simple message',)"
+    strexp = "OverflowException('Simple message"
+    assert repr(e)[:len(strexp)] == strexp
 
 
 def test_exception_is_instance_of_system_object():

src/tests/test_repr.py

@@ -0,0 +1,68 @@
+# -*- coding: utf-8 -*-
+
+"""Test __repr__ output"""
+
+import System
+import pytest
+from Python.Test import ReprTest
+
+def test_basic():
+    """Test Point class which implements both ToString and __repr__ without inheritance"""
+    ob = ReprTest.Point(1,2)
+    # point implements ToString() and __repr__()
+    assert ob.__repr__() == "Point(1,2)"
+    assert str(ob) == "Python.Test.ReprTest+Point: X=1, Y=2"
+
+def test_system_string():
+    """Test system string"""
+    ob = System.String("hello")
+    assert str(ob) == "hello"
+    assert "<System.String object at " in ob.__repr__()
+
+def test_str_only():
+    """Test class implementing ToString() but not __repr__()"""
+    ob = ReprTest.Bar()
+    assert str(ob) == "I implement ToString() but not __repr__()!"
+    assert "<Python.Test.Bar object at " in ob.__repr__()
+
+def test_hierarchy1():
+    """Test inheritance heirarchy with base & middle class implementing ToString"""
+    ob1 = ReprTest.BazBase()
+    assert str(ob1) == "Base class implementing ToString()!"
+    assert "<Python.Test.BazBase object at " in ob1.__repr__()
+
+    ob2 = ReprTest.BazMiddle()
+    assert str(ob2) == "Middle class implementing ToString()!"
+    assert "<Python.Test.BazMiddle object at " in ob2.__repr__()
+
+    ob3 = ReprTest.Baz()
+    assert str(ob3) == "Middle class implementing ToString()!"
+    assert "<Python.Test.Baz object at " in ob3.__repr__()
+
+def bad_tostring():
+    """Test ToString that can't be used by str()"""
+    ob = ReprTest.Quux()
+    assert str(ob) == "Python.Test.ReprTest+Quux"
+    assert "<Python.Test.Quux object at " in ob.__repr__()
+
+def bad_repr():
+    """Test incorrect implementation of repr"""
+    ob1 = ReprTest.QuuzBase()
+    assert str(ob1) == "Python.Test.ReprTest+QuuzBase"
+    assert "<Python.Test.QuuzBase object at " in ob.__repr__()
+    
+    ob2 = ReprTest.Quuz()
+    assert str(ob2) == "Python.Test.ReprTest+Quuz"
+    assert "<Python.Test.Quuz object at " in ob.__repr__()
+
+    ob3 = ReprTest.Corge()
+    with pytest.raises(Exception):
+        str(ob3)
+    with pytest.raises(Exception):
+        ob3.__repr__()
+
+    ob4 = ReprTest.Grault()
+    with pytest.raises(Exception):
+        str(ob4)
+    with pytest.raises(Exception):
+        ob4.__repr__()

src/tests/tests.pyproj

@@ -59,6 +59,7 @@
     <Compile Include="test_recursive_types.py" />
     <Compile Include="test_subclass.py" />
     <Compile Include="test_thread.py" />
+    <Compile Include="test_repr.py" />
     <Compile Include="utils.py" />
     <Compile Include="fixtures\argv-fixture.py" />
   </ItemGroup>