Raise a custom error if the RDB is an error report

dataretrieval/exceptions.py

@@ -0,0 +1,6 @@
+class DataRetrievalError(BaseException):
+    """Base exception for dataretrieval"""
+
+
+class EmptyQueryResultError(DataRetrievalError):
+    """Raised when a query returns an error"""

dataretrieval/nwis.py

@@ -11,6 +11,7 @@
 from io import StringIO
 
 from dataretrieval.utils import to_str, format_datetime, update_merge, set_metadata as set_md
+from .exceptions import EmptyQueryResultError
 from .utils import query
 
 WATERDATA_BASE_URL = 'https://nwis.waterdata.usgs.gov/'
@@ -709,6 +710,10 @@ def _read_rdb(rdb):
     fields = rdb.splitlines()[count].split('\t')
     dtypes = {'site_no': str, 'dec_long_va': float, 'dec_lat_va': float}
 
+    # raise error if result has error
+    if "Error report" in (fields[0]):
+        raise EmptyQueryResultError
+
     df = pd.read_csv(StringIO(rdb), delimiter='\t', skiprows=count + 2,
                      names=fields, na_values='NaN', dtype=dtypes)
 

tests/nwis_test.py

@@ -1,5 +1,7 @@
 import pytest
-from dataretrieval.nwis import get_record
+
+from dataretrieval.exceptions import EmptyQueryResultError
+from dataretrieval.nwis import get_record, _read_rdb
 
 START_DATE = '2018-01-24'
 END_DATE   = '2018-01-25'
@@ -39,6 +41,11 @@ def test_iv_service_answer():
     assert df.index.names == [SITENO_COL, DATETIME_COL], "iv service returned incorrect index: {}".format(df.index.names)
 
 
+def test_read_rdb_raises_error():
+    with pytest.raises(EmptyQueryResultError):
+        _read_rdb("Error report")
+
+
 if __name__=='__main__':
      test_measurements_service_answer()
      test_iv_service_answer()