conditional import, constants, example fix

Author: AVanVlack

README.rst

@@ -92,10 +92,10 @@ For humidity compensated raw gas and voc index readings, we'll need a secondary
         humidity = bme280.relative_humidity
 
         # For compensated raw gas readings
-        compensated_raw_gas = sgp.measure_index(temperature = temperature, relative_humidity = humidity)
+        compensated_raw_gas = sgp.raw(temperature = temperature, relative_humidity = humidity)
 
         # For Compensated voc index readings
-        voc_index = sgp.measure_raw(temperature = temperature, relative_humidity = humidity)
+        voc_index = sgp.measure_index(temperature = temperature, relative_humidity = humidity)
 
         print(compensated_raw_gas)
         print(voc_index)

adafruit_sgp40/__init__.py

@@ -32,7 +32,6 @@
 from time import sleep
 from struct import unpack_from
 from adafruit_bus_device import i2c_device
-from adafruit_sgp40.voc_algorithm import VOCAlgorithm
 
 __version__ = "0.0.0-auto.0"
 __repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_SGP40.git"
@@ -112,7 +111,7 @@ def __init__(self, i2c, address=0x59):
         self.i2c_device = i2c_device.I2CDevice(i2c, address)
         self._command_buffer = bytearray(2)
         self._measure_command = _READ_CMD
-        self._voc_algorithm = VOCAlgorithm()
+        self._voc_algorithm = None
 
         self.initialize()
 
@@ -135,8 +134,6 @@ def initialize(self):
 
             raise RuntimeError("Feature set does not match: %s" % hex(featureset[0]))
 
-        self._voc_algorithm.vocalgorithm_init()
-
         # Self Test
         self._command_buffer[0] = 0x28
         self._command_buffer[1] = 0x0E
@@ -234,12 +231,22 @@ def measure_index(self, temperature=25, relative_humidity=50):
         :param float relative_humidity: The relative humidity in percentage, defaults to :const:`50`
         :note  VOC index can indicate the quality of the air directly.
         The larger the value, the worse the air quality.
-        :note 0-100,no need to ventilate, purify
-        :note 100-200,no need to ventilate, purify
-        :note 200-400,ventilate, purify
-        :note 00-500,ventilate, purify intensely
+        :note 0-100, no need to ventilate, purify
+        :note 100-200, no need to ventilate, purify
+        :note 200-400, ventilate, purify
+        :note 00-500, ventilate, purify intensely
         :return int The VOC index measured, ranged from 0 to 500
         """
+        # import/setup algorithm only on use of index
+        # pylint: disable=import-outside-toplevel
+        from adafruit_sgp40.voc_algorithm import (
+            VOCAlgorithm,
+        )
+
+        if self._voc_algorithm is None:
+            self._voc_algorithm = VOCAlgorithm()
+            self._voc_algorithm.vocalgorithm_init()
+
         raw = self.measure_raw(temperature, relative_humidity)
         if raw < 0:
             return -1