In-Reply-To=<4EA045E4.9020508@anaproy.nl> Has there been any advancements regarding this memory leak? I built the newest version of lxml (as well as its dependencies) and the problem is still there. I was able to track it down using umdh on Windows: etree!xmlDictLookup+0000025E (c:\tmp\libxml2-win-binaries\libxml2\dict.c, 933) etree!xmlHashAddEntry3+00000053 (c:\tmp\libxml2-win-binaries\libxml2\hash.c, 532) etree!xmlHashAddEntry+00000014 (c:\tmp\libxml2-win-binaries\libxml2\hash.c, 377) etree!xmlAddID+0000011D (c:\tmp\libxml2-win-binaries\libxml2\valid.c, 2632) etree!xmlSAX2AttributeInternal+0000078A (c:\tmp\libxml2-win-binaries\libxml2\sax2.c, 1411) etree!xmlSAX2StartElement+000002AE (c:\tmp\libxml2-win-binaries\libxml2\sax2.c, 1743) etree!htmlParseStartTag+00000579 (c:\tmp\libxml2-win-binaries\libxml2\htmlparser.c, 3926) etree!htmlParseElementInternal+00000069 (c:\tmp\libxml2-win-binaries\libxml2\htmlparser.c, 4467) etree!htmlParseContentInternal+000003D3 (c:\tmp\libxml2-win-binaries\libxml2\htmlparser.c, 4652) etree!htmlParseDocument+000002A2 (c:\tmp\libxml2-win-binaries\libxml2\htmlparser.c, 4818) etree!htmlDoRead+00000094 (c:\tmp\libxml2-win-binaries\libxml2\htmlparser.c, 6786) etree!htmlCtxtReadMemory+00000093 (c:\tmp\libxml2-win-binaries\libxml2\htmlparser.c, 7072) etree!__pyx_f_4lxml_5etree_11_BaseParser__parseUnicodeDoc+0000028A (c:\tmp\lxml-3.6.4\src\lxml\lxml.etree.c, 109222) etree!__pyx_f_4lxml_5etree__parseDoc+0000041F (c:\tmp\lxml-3.6.4\src\lxml\lxml.etree.c, 115220) etree!__pyx_f_4lxml_5etree__parseMemoryDocument+000000E6 (c:\tmp\lxml-3.6.4\src\lxml\lxml.etree.c, 116674) etree!__pyx_pf_4lxml_5etree_22fromstring+00000086 (c:\tmp\lxml-3.6.4\src\lxml\lxml.etree.c, 77737) etree!__pyx_pw_4lxml_5etree_23fromstring+00000294 (c:\tmp\lxml-3.6.4\src\lxml\lxml.etree.c, 77687) python33!PyCFunction_Call+000000F3 (c:\users\martin\33.amd64\python\objects\methodobject.c, 84) python33!PyObject_Call+00000061 (c:\users\martin\33.amd64\python\objects\abstract.c, 2036) python33!ext_do_call+00000295 (c:\users\martin\33.amd64\python\python\ceval.c, 4381) python33!PyEval_EvalFrameEx+00002041 (c:\users\martin\33.amd64\python\python\ceval.c, 2723) python33!PyEval_EvalCodeEx+0000065C (c:\users\martin\33.amd64\python\python\ceval.c, 3436) python33!function_call+0000015D (c:\users\martin\33.amd64\python\objects\funcobject.c, 639) python33!PyObject_Call+00000061 (c:\users\martin\33.amd64\python\objects\abstract.c, 2036) python33!ext_do_call+00000295 (c:\users\martin\33.amd64\python\python\ceval.c, 4381) python33!PyEval_EvalFrameEx+00002041 (c:\users\martin\33.amd64\python\python\ceval.c, 2723) python33!PyEval_EvalCodeEx+0000065C (c:\users\martin\33.amd64\python\python\ceval.c, 3436) python33!fast_function+0000014D (c:\users\martin\33.amd64\python\python\ceval.c, 4168) python33!call_function+00000339 (c:\users\martin\33.amd64\python\python\ceval.c, 4088) python33!PyEval_EvalFrameEx+00001F98 (c:\users\martin\33.amd64\python\python\ceval.c, 2681) For reference, here are my version numbers: Python : sys.version_info(major=3, minor=3, micro=5, releaselevel='final', serial=0) lxml.etree : (3, 6, 4, 0) libxml used : (2, 9, 4) libxml compiled : (2, 9, 4) libxslt used : (1, 1, 29) libxslt compiled : (1, 1, 29) Should I open a new bug? Thanks! Benoit Bernard https://benbernardblog.com