qgis-errors-data-loading

Quick Reference

The #1 Rule

ALWAYS call layer.isValid() immediately after creating ANY layer. An invalid layer does NOT raise an exception — it silently returns a broken object that crashes or produces undefined behavior on access.

layer = QgsVectorLayer(uri, name, provider)
if not layer.isValid():
    raise RuntimeError(f"Failed to load layer '{name}': check URI, provider, and data source")

Error Categories at a Glance