refactor: Need to import PerformanceWarning to test module

src/transport_performance/osm/validate_osm.py

@@ -18,6 +18,8 @@
 * Find coordinates for node or way features
 * Plot the coordinates of a given list of node or way IDs
 """
+import os
+import warnings
 from pathlib import Path
 from typing import Union
 
@@ -37,6 +39,12 @@
 # ---------utilities-----------
 
 
+class PerformanceWarning(UserWarning):
+    """Operation may be slow."""
+
+    pass
+
+
 def _compile_tags(osmium_feature):
     """Return tag name value pairs.
 
@@ -553,6 +561,16 @@ def __init__(
         _is_expected_filetype(
             osm_pth, "osm_pth", check_existing=True, exp_ext=".pbf"
         )
+        self.large_file_thresh = 50000  # 50 KB
+        # implement performance warning on large OSM files.
+        osm_size = os.path.getsize(osm_pth)
+        if osm_size > self.large_file_thresh:
+            warnings.warn(
+                f"PBF file is {osm_size} bytes. Tag operations are expensive."
+                " Consider filtering the pbf file smaller than"
+                f" {self.large_file_thresh} bytes",
+                PerformanceWarning,
+            )
         tags = tag_collator()
         classnm = tags.__class__.__name__
         if classnm != "_TagHandler":