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danabr opened this issue Sep 23, 2020 · 1 comment · Fixed by #1241
Closed

.NET class instances considered Iterable #1234

danabr opened this issue Sep 23, 2020 · 1 comment · Fixed by #1241

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@danabr
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danabr commented Sep 23, 2020

Environment

  • Pythonnet version: 2.5.0
  • Python version: 3.7
  • Operating System: Windows

Details

All .NET class instances are considered instances of collections.abc.Iterable.

namespace Python.Test {
  public class Empty { }
}
def test_not_Iterable():
    """Test regular .NET objects are not iterable"""
    from Python.Test import Empty
    from collections.abc import Iterable

    assert (not isinstance(Empty(), Iterable))

The test is expected to pass, but fails:

    def test_not_Iterable():
        """Test regular .NET objects are not iterable"""
        from Python.Test import Empty
        from collections.abc import Iterable

>       assert (not isinstance(Empty(), Iterable))
E       AssertionError: assert not True
E        +  where True = isinstance(<Python.Test.Empty object at 0x0000022D3E6DE5C8>, <class 'collections.abc.Iterable'>)
E        +    where <Python.Test.Empty object at 0x0000022D3E6DE5C8> = <class 'Python.Test.Empty'>()
@filmor
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filmor commented Sep 24, 2020 •
edited
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This is because the tp_iter slot is always filled and just throws an error for non-IEnumerable types:

pythonnet/src/runtime/classbase.cs

Lines 181 to 207 in 742463e

public static IntPtr tp_iter(IntPtr ob)
{
var co = GetManagedObject(ob) as CLRObject;
if (co == null)
{
return Exceptions.RaiseTypeError("invalid object");
}
var e = co.inst as IEnumerable;
IEnumerator o;
if (e != null)
{
o = e.GetEnumerator();
}
else
{
o = co.inst as IEnumerator;
if (o == null)
{
return Exceptions.RaiseTypeError("iteration over non-sequence");
}
}
return new Iterator(o).pyHandle;
}

We could do the respective check in the "constructor" of the type here:

pythonnet/src/runtime/typemanager.cs

Lines 683 to 723 in ec424bb

/// <summary>
/// Given a newly allocated Python type object and a managed Type that
/// provides the implementation for the type, connect the type slots of
/// the Python object to the managed methods of the implementing Type.
/// </summary>
internal static void InitializeSlots(IntPtr type, Type impl)
{
// We work from the most-derived class up; make sure to get
// the most-derived slot and not to override it with a base
// class's slot.
var seen = new HashSet<string>();
while (impl != null)
{
MethodInfo[] methods = impl.GetMethods(tbFlags);
foreach (MethodInfo method in methods)
{
string name = method.Name;
if (!(name.StartsWith("tp_") ||
name.StartsWith("nb_") ||
name.StartsWith("sq_") ||
name.StartsWith("mp_") ||
name.StartsWith("bf_")
))
{
continue;
}
if (seen.Contains(name))
{
continue;
}
var thunkInfo = Interop.GetThunk(method);
InitializeSlot(type, thunkInfo.Address, name);
seen.Add(name);
}
impl = impl.BaseType;
}

danabr added a commit to danabr/pythonnet that referenced this issue Sep 26, 2020
@danabr
Ensure only implementers of IEnumerable or IEnumerator are considered…
df88072 
… Iterable

Fixes pythonnet#1234.
@danabr danabr mentioned this issue Sep 26, 2020
Merged
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danabr added a commit to danabr/pythonnet that referenced this issue Sep 28, 2020
@danabr
Ensure only implementers of IEnumerable or IEnumerator are considered…
60ba5d7 
… Iterable

Fixes pythonnet#1234.
lostmsu pushed a commit that referenced this issue Sep 29, 2020
@danabr
Ensure only implementers of IEnumerable or IEnumerator are considered…
b5ba815 
… Iterable (#1241)

Fixes #1234.

Previously `tp_iter` slot was set for all reflected .NET types. This restricts it to types, that implement `IEnumerable` or `IEnumerator`
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Ensure only implementers of IEnumerable or IEnumerator are considered Iterable danabr/pythonnet
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@filmor @danabr