diff -uNr qemu-4.1.1/scripts/tracetool/__init__.py qemu-4.1.1.mod/scripts/tracetool/__init__.py
--- qemu-4.1.1/scripts/tracetool/__init__.py	2019-11-14 20:06:21.000000000 +0200
+++ qemu-4.1.1.mod/scripts/tracetool/__init__.py	2020-05-06 15:01:10.683357477 +0300
@@ -453,12 +453,12 @@
     import tracetool
 
     format = str(format)
-    if len(format) is 0:
+    if len(format) == 0:
         raise TracetoolError("format not set")
     if not tracetool.format.exists(format):
         raise TracetoolError("unknown format: %s" % format)
 
-    if len(backends) is 0:
+    if len(backends) == 0:
         raise TracetoolError("no backends specified")
     for backend in backends:
         if not tracetool.backend.exists(backend):