fixed issues where usecols became a required input

Author: eicchen

pandas/io/parsers/readers.py

@@ -1519,7 +1519,7 @@ def read(self, nrows: int | None = None) -> DataFrame:
 
             if hasattr(self, "orig_options"):
                 dtype_arg = self.orig_options.get("dtype", None)
-                usecols = self.orig_options["usecols"]
+                usecols = self.orig_options.get("usecols", None)
             else:
                 dtype_arg = None
                 usecols = None