Fix flake regressions

Author: doyle-arista

influxdb/__init__.py

@@ -17,9 +17,10 @@
     'SeriesHelper',
 ]
 
-if os.environ.get("INFLUXDB_NO_DATAFRAME_CLIENT", "0").lower() not in ("1", "true"):
-   from .dataframe_client import DataFrameClient
-   __all__.append( "DataFrameClient" )
+NO_DATAFRAME_CLIENT = os.environ.get("INFLUXDB_NO_DATAFRAME_CLIENT", "0")
+if NO_DATAFRAME_CLIENT.lower() not in ("1", "true"):
+    from .dataframe_client import DataFrameClient # noqa: F401 unused import
+     __all__.append("DataFrameClient")
 
 
 __version__ = '5.0.0'