Avoid repeated initialization of the shim module

When the shim module tries to reload itself, it repeats the loop of
trying all the sitepackages directories, and because importlib.reload()
is noop when called recursively, it ends up raising ImportError that is
visible to the user. Even though execution returns to the original loop
and the system RPM module is loaded successfully, the error message
produced is very confusing.

Improve that by avoiding repeated initialization of the shim module.
Also make sure that importlib.reload(), when loading the shim module for
the second time, throws a specific exception that doesn't trigger any
log message, to make things even less confusing.

Signed-off-by: Nikola Forró <[email protected]>

rpm/__init__.py

@@ -20,6 +20,10 @@
 logger = logging.getLogger(PROJECT_NAME)
 
 
+class ShimAlreadyInitializingError(Exception):
+    pass
+
+
 def get_system_sitepackages() -> List[str]:
     """
     Gets a list of sitepackages directories of system Python interpreter(s).
@@ -71,7 +75,7 @@ def try_path(path: str) -> bool:
     return False
 
 
-def init_module() -> None:
+def initialize() -> None:
     """
     Initializes the shim. Tries to load system RPM module and replace itself with it.
     """
@@ -81,11 +85,20 @@ def init_module() -> None:
             if try_path(path):
                 logger.debug("Import successfull")
                 return
+        except ShimAlreadyInitializingError:
+            continue
         except Exception as e:
             logger.error(f"Exception: {e}")
             continue
     else:
         raise ImportError("Failed to import system RPM module")
 
 
-init_module()
+# avoid repeated initialization of the shim module
+try:
+    _shim_module_initializing_
+except NameError:
+    _shim_module_initializing_: bool = True
+    initialize()
+else:
+    raise ShimAlreadyInitializingError