Parquet: Add error message for no engine found (#18717)

* patquet.py: Add error message for no engine found Give a better error message for engine="auto" case when none of the engines were found installed. * clean-up to prevent merge conflicts with other PR

Author: jorisvandenbossche

pandas/io/parquet.py

@@ -25,6 +25,11 @@ def get_engine(engine):
  except ImportError:
  pass
 
+ raise ImportError("Unable to find a usable engine; "
+ "tried using: 'pyarrow', 'fastparquet'.\n"
+ "pyarrow or fastparquet is required for parquet "
+ "support")
+
  if engine not in ['pyarrow', 'fastparquet']:
  raise ValueError("engine must be one of 'pyarrow', 'fastparquet'")