fix import order and reduce __init__ complexity

Author: seemanne

maxminddb/reader.py

@@ -64,30 +64,21 @@ def __init__(
                               a path. This mode implies MODE_MEMORY.
 
         """
-        filename: Any
         if (mode == MODE_AUTO and mmap) or mode == MODE_MMAP:
             with open(database, "rb") as db_file:  # type: ignore[arg-type]
                 self._buffer = mmap.mmap(db_file.fileno(), 0, access=mmap.ACCESS_READ)
                 self._buffer_size = self._buffer.size()
-            filename = database
         elif mode in (MODE_AUTO, MODE_FILE):
             self._buffer = FileBuffer(database)  # type: ignore[arg-type]
             self._buffer_size = self._buffer.size()
-            filename = database
         elif mode == MODE_MEMORY:
             with open(database, "rb") as db_file:  # type: ignore[arg-type]
                 buf = db_file.read()
                 self._buffer = buf
                 self._buffer_size = len(buf)
-            filename = database
         elif mode == MODE_FD:
             self._buffer = database.read()  # type: ignore[union-attr]
             self._buffer_size = len(self._buffer)  # type: ignore[arg-type]
-            # io buffers are not guaranteed to have a name attribute
-            if hasattr(database, "name"):
-                filename = database.name  # type: ignore[union-attr]
-            else:
-                filename = f"<{type(database)}>"
         else:
             msg = (
                 f"Unsupported open mode ({mode}). Only MODE_AUTO, MODE_FILE, "
@@ -97,6 +88,8 @@ def __init__(
             raise ValueError(
                 msg,
             )
+        # io buffers are not guaranteed to have a name attribute
+        filename = database.name if hasattr(database, "name") else f"<{type(database)}>"
 
         metadata_start = self._buffer.rfind(
             self._METADATA_START_MARKER,

tests/reader_test.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
-import ipaddress
 import io
+import ipaddress
 import multiprocessing
 import os
 import pathlib