Allow skipping DataFrameClient import

Importing the DataFrameClient can take quite a while,
especially when the source files aren't yet loaded into
the page cache.

This patch adds an environment variable, INFLUXDB_NO_DATAFRAME_CLIENT,
to allow users of this package to skip this import in cases where
they don't need it.

Author: doyle-arista

docs/source/api-documentation.rst

@@ -10,6 +10,10 @@ To connect to a InfluxDB, you must create a
 connects to InfluxDB on ``localhost`` with the default
 ports. The below instantiation statements are all equivalent::
 
+    # Set INFLUXDB_NO_DATAFRAME_CLIENT to skip the expensive DataFrameClient
+    # import in cases where you only need the basic InfluxDBClient.
+    os.environ["INFLUXDB_NO_DATAFRAME_CLIENT"] = "1"
+
     from influxdb import InfluxDBClient
 
     # using Http

examples/tutorial.py

@@ -3,6 +3,8 @@
 
 import argparse
 
+import os
+os.environ["INFLUXDB_NO_DATAFRAME_CLIENT"] = "1"
 from influxdb import InfluxDBClient
 
 

influxdb/__init__.py

@@ -6,16 +6,20 @@
 from __future__ import print_function
 from __future__ import unicode_literals
 
+import os
+
 from .client import InfluxDBClient
-from .dataframe_client import DataFrameClient
 from .helper import SeriesHelper
 
 
 __all__ = [
     'InfluxDBClient',
-    'DataFrameClient',
     'SeriesHelper',
 ]
 
+if "INFLUXDB_NO_DATAFRAME_CLIENT" not in os.environ:
+   from .dataframe_client import DataFrameClient
+   __all__.append( "DataFrameClient" )
+
 
 __version__ = '5.0.0'