[fix] Improve error message when trying to open zipfile with Python 3.6

core/ratarmountcore/SQLiteIndexedTar.py

@@ -2077,6 +2077,9 @@ def _detectCompression(fileobj: IO[bytes], printDebug: int = 0) -> Optional[str]
 
         oldOffset = fileobj.tell()
         for compressionId, compression in supportedCompressions.items():
+            if compressionId in ['rar', 'zip']:
+                continue
+
             # The header check is a necessary condition not a sufficient condition.
             # Especially for gzip, which only has 2 magic bytes, false positives might happen.
             # Therefore, only use the magic bytes based check if the module could not be found

core/ratarmountcore/compressions.py

@@ -50,7 +50,7 @@
 # The file object returned by ZipFile.open is not seekable in Python 3.6 for some reason.
 # Therefore disable ZIP support there!
 # I don't see it documented, instead I tested different Python versions with Docker.
-if sys.version_info[1] > 6:
+if sys.version_info[0] == 3 and sys.version_info[1] > 6:
     import zipfile
 else:
     zipfile = None

core/ratarmountcore/factory.py

@@ -57,7 +57,7 @@ def openMountSource(fileOrPath: Union[str, IO[bytes]], **options) -> MountSource
         if hasattr(fileOrPath, 'seek'):
             fileOrPath.seek(0)  # type: ignore
 
-    if 'zipfile' in sys.modules:
+    if 'zipfile' in sys.modules and zipfile is not None:
         try:
             # is_zipfile is much too lax when testing for ZIPs because it's only testing for the central directory
             # at the end of the file not the magic bits at the beginning. Meaning, if another non-ZIP archive has