Hello, While using Python.NET in one of my projects I found some problems: 1. PythonException uses Runtime.PyErr_Fetch before calling AcquireLock, which is wrong. Here's the patch: --- src/runtime/pythonexception.cs (revision 138) +++ src/runtime/pythonexception.cs (working copy) @@ -27,11 +27,11 @@ public PythonException() : base() { + IntPtr gs = PythonEngine.AcquireLock(); Runtime.PyErr_Fetch(ref _pyType, ref _pyValue, ref _pyTB); Runtime.Incref(_pyType); Runtime.Incref(_pyValue); Runtime.Incref(_pyTB); - IntPtr gs = PythonEngine.AcquireLock(); if ((_pyType != IntPtr.Zero) && (_pyValue != IntPtr.Zero)) { string type = new PyObject(_pyType).GetAttr("__name__").ToString(); 2. Every time .NET code throws an exception Python.NET leaks memory, because exception object is not decref'ed after calling PyErr_SetObject. In my case there were lots of exceptions, so problem was very noticable over time. Here's the patch: -- src/runtime/exceptions.cs (revision 138) +++ src/runtime/exceptions.cs (working copy) @@ -473,6 +473,7 @@ IntPtr etype = Runtime.PyObject_GetAttrString(op, "__class__"); Runtime.PyErr_SetObject(etype, op); Runtime.Decref(etype); + Runtime.Decref(op); } /// <summary> Hope this helps others in their fights for thread safety and against memory leaks. :) Thanks, Alexey.