diff --git a/.gitignore b/.gitignore
index 810752e..5efe1d1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -19,3 +19,7 @@ library/debian/
 pip-log.txt
 pip-delete-this-directory.txt
 .DS_Store
+.vscode/
+.coverage
+.tox/
+.pytest_cache/
diff --git a/.travis.yml b/.travis.yml
index 22d7e8c..42479fe 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,10 +1,24 @@
 language: python
 sudo: false
+cache: pip
+
+git:
+  submodules: true
 
 matrix:
-        include:
-                python: "2.7"
+  include:
+    - python: "2.7"
+      env: TOXENV=py27
+    - python: "3.5"
+      env: TOXENV=py35
+    - python: "2.7"
+      env: TOXENV=py27
+
+install:
+  - pip install --ignore-installed --upgrade setuptools pip tox coveralls
 
 script:
-        - pip install --ignore-installed --upgrade flake8
-        - flake8 --ignore F403,F405,E501
+  - cd library
+  - tox -vv
+
+after_success: if [ "$TOXENV" == "py35" ]; then coveralls; fi
diff --git a/examples/indoor-air-quality.py b/examples/indoor-air-quality.py
index bf68fa9..760cce9 100755
--- a/examples/indoor-air-quality.py
+++ b/examples/indoor-air-quality.py
@@ -1,11 +1,10 @@
 #!/usr/bin/env python
-
 import bme680
 import time
 
 print("""Estimate indoor air quality
 
-Runs the sensor for a burn-in period, then uses a 
+Runs the sensor for a burn-in period, then uses a
 combination of relative humidity and gas resistance
 to estimate indoor air quality as a percentage.
 
@@ -15,7 +14,7 @@ Press Ctrl+C to exit
 
 sensor = bme680.BME680()
 
-# These oversampling settings can be tweaked to 
+# These oversampling settings can be tweaked to
 # change the balance between accuracy and noise in
 # the data.
 
@@ -29,7 +28,7 @@ sensor.set_gas_heater_temperature(320)
 sensor.set_gas_heater_duration(150)
 sensor.select_gas_heater_profile(0)
 
-# start_time and curr_time ensure that the 
+# start_time and curr_time ensure that the
 # burn_in_time (in seconds) is kept track of.
 
 start_time = time.time()
@@ -42,13 +41,13 @@ try:
     # Collect gas resistance burn-in values, then use the average
     # of the last 50 values to set the upper limit for calculating
     # gas_baseline.
-    print("Collecting gas resistance burn-in data for 5 mins\n")
+    print('Collecting gas resistance burn-in data for 5 mins\n')
     while curr_time - start_time < burn_in_time:
         curr_time = time.time()
         if sensor.get_sensor_data() and sensor.data.heat_stable:
             gas = sensor.data.gas_resistance
             burn_in_data.append(gas)
-            print("Gas: {0} Ohms".format(gas))
+            print('Gas: {0} Ohms'.format(gas))
             time.sleep(1)
 
     gas_baseline = sum(burn_in_data[-50:]) / 50.0
@@ -56,11 +55,13 @@ try:
     # Set the humidity baseline to 40%, an optimal indoor humidity.
     hum_baseline = 40.0
 
-    # This sets the balance between humidity and gas reading in the 
+    # This sets the balance between humidity and gas reading in the
     # calculation of air_quality_score (25:75, humidity:gas)
     hum_weighting = 0.25
 
-    print("Gas baseline: {0} Ohms, humidity baseline: {1:.2f} %RH\n".format(gas_baseline, hum_baseline))
+    print('Gas baseline: {0} Ohms, humidity baseline: {1:.2f} %RH\n'.format(
+        gas_baseline,
+        hum_baseline))
 
     while True:
         if sensor.get_sensor_data() and sensor.data.heat_stable:
@@ -72,22 +73,31 @@ try:
 
             # Calculate hum_score as the distance from the hum_baseline.
             if hum_offset > 0:
-                hum_score = (100 - hum_baseline - hum_offset) / (100 - hum_baseline) * (hum_weighting * 100)
+                hum_score = (100 - hum_baseline - hum_offset)
+                hum_score /= (100 - hum_baseline)
+                hum_score *= (hum_weighting * 100)
 
             else:
-                hum_score = (hum_baseline + hum_offset) / hum_baseline * (hum_weighting * 100)
+                hum_score = (hum_baseline + hum_offset)
+                hum_score /= hum_baseline
+                hum_score *= (hum_weighting * 100)
 
             # Calculate gas_score as the distance from the gas_baseline.
             if gas_offset > 0:
-                gas_score = (gas / gas_baseline) * (100 - (hum_weighting * 100))
+                gas_score = (gas / gas_baseline)
+                gas_score *= (100 - (hum_weighting * 100))
 
             else:
                 gas_score = 100 - (hum_weighting * 100)
 
-            # Calculate air_quality_score. 
+            # Calculate air_quality_score.
             air_quality_score = hum_score + gas_score
 
-            print("Gas: {0:.2f} Ohms,humidity: {1:.2f} %RH,air quality: {2:.2f}".format(gas, hum, air_quality_score))
+            print('Gas: {0:.2f} Ohms,humidity: {1:.2f} %RH,air quality: {2:.2f}'.format(
+                gas,
+                hum,
+                air_quality_score))
+
             time.sleep(1)
 
 except KeyboardInterrupt:
diff --git a/examples/read-all.py b/examples/read-all.py
index 24baef5..fe24da1 100755
--- a/examples/read-all.py
+++ b/examples/read-all.py
@@ -1,23 +1,28 @@
 #!/usr/bin/env python
-
 import bme680
 import time
 
+print("""Display Temperature, Pressure, Humidity and Gas
+
+Press Ctrl+C to exit
+
+""")
+
 sensor = bme680.BME680()
 
 # These calibration data can safely be commented
 # out, if desired.
 
-print("Calibration data:")
+print('Calibration data:')
 for name in dir(sensor.calibration_data):
 
     if not name.startswith('_'):
         value = getattr(sensor.calibration_data, name)
 
         if isinstance(value, int):
-            print("{}: {}".format(name, value))
+            print('{}: {}'.format(name, value))
 
-# These oversampling settings can be tweaked to 
+# These oversampling settings can be tweaked to
 # change the balance between accuracy and noise in
 # the data.
 
@@ -27,12 +32,12 @@ sensor.set_temperature_oversample(bme680.OS_8X)
 sensor.set_filter(bme680.FILTER_SIZE_3)
 sensor.set_gas_status(bme680.ENABLE_GAS_MEAS)
 
-print("\n\nInitial reading:")
+print('\n\nInitial reading:')
 for name in dir(sensor.data):
     value = getattr(sensor.data, name)
 
     if not name.startswith('_'):
-        print("{}: {}".format(name, value))
+        print('{}: {}'.format(name, value))
 
 sensor.set_gas_heater_temperature(320)
 sensor.set_gas_heater_duration(150)
@@ -43,14 +48,19 @@ sensor.select_gas_heater_profile(0)
 # sensor.set_gas_heater_profile(200, 150, nb_profile=1)
 # sensor.select_gas_heater_profile(1)
 
-print("\n\nPolling:")
+print('\n\nPolling:')
 try:
     while True:
         if sensor.get_sensor_data():
-            output = "{0:.2f} C,{1:.2f} hPa,{2:.2f} %RH".format(sensor.data.temperature, sensor.data.pressure, sensor.data.humidity)
+            output = '{0:.2f} C,{1:.2f} hPa,{2:.2f} %RH'.format(
+                sensor.data.temperature,
+                sensor.data.pressure,
+                sensor.data.humidity)
 
             if sensor.data.heat_stable:
-                print("{0},{1} Ohms".format(output, sensor.data.gas_resistance))
+                print('{0},{1} Ohms'.format(
+                    output,
+                    sensor.data.gas_resistance))
 
             else:
                 print(output)
diff --git a/examples/setup.cfg b/examples/setup.cfg
new file mode 100644
index 0000000..9e0f472
--- /dev/null
+++ b/examples/setup.cfg
@@ -0,0 +1,8 @@
+[flake8]
+ignore =
+	E501  # line too long
+	F403
+	F405
+# Don't require docstrings in example code
+    D100  # Missing docstring in public module
+    D103  # Missing docstring in public function
diff --git a/examples/temp-offset.py b/examples/temp-offset.py
index 3f468b4..fba26c7 100755
--- a/examples/temp-offset.py
+++ b/examples/temp-offset.py
@@ -15,25 +15,29 @@ sensor.set_pressure_oversample(bme680.OS_4X)
 sensor.set_temperature_oversample(bme680.OS_8X)
 sensor.set_filter(bme680.FILTER_SIZE_3)
 
+
 def display_data(offset=0):
     sensor.set_temp_offset(offset)
     sensor.get_sensor_data()
-    output = "{0:.2f} C, {1:.2f} hPa, {2:.3f} %RH".format(sensor.data.temperature, sensor.data.pressure, sensor.data.humidity)
+    output = '{0:.2f} C, {1:.2f} hPa, {2:.3f} %RH'.format(
+        sensor.data.temperature,
+        sensor.data.pressure,
+        sensor.data.humidity)
     print(output)
-    print("")
+    print('')
 
-print("Initial readings")
+
+print('Initial readings')
 display_data()
 
-print("SET offset 4 degrees celsius")
+print('SET offset 4 degrees celsius')
 display_data(4)
 
-print("SET offset -1.87 degrees celsius")
+print('SET offset -1.87 degrees celsius')
 display_data(-1.87)
 
-print("SET offset -100 degrees celsius")
+print('SET offset -100 degrees celsius')
 display_data(-100)
 
-print("SET offset 0 degrees celsius")
+print('SET offset 0 degrees celsius')
 display_data(0)
-
diff --git a/examples/temp-press-hum.py b/examples/temp-press-hum.py
index b21d0f4..af32ad8 100755
--- a/examples/temp-press-hum.py
+++ b/examples/temp-press-hum.py
@@ -1,6 +1,5 @@
 #!/usr/bin/env python
 import bme680
-import time
 
 print("""Display Temperature, Pressure and Humidity
 
@@ -22,15 +21,17 @@ sensor.set_pressure_oversample(bme680.OS_4X)
 sensor.set_temperature_oversample(bme680.OS_8X)
 sensor.set_filter(bme680.FILTER_SIZE_3)
 
-print("Polling:")
+print('Polling:')
 try:
     while True:
         if sensor.get_sensor_data():
 
-            output = "{0:.2f} C,{1:.2f} hPa,{2:.3f} %RH".format(sensor.data.temperature, sensor.data.pressure, sensor.data.humidity)
+            output = '{0:.2f} C,{1:.2f} hPa,{2:.3f} %RH'.format(
+                sensor.data.temperature,
+                sensor.data.pressure,
+                sensor.data.humidity)
 
             print(output)
 
 except KeyboardInterrupt:
     pass
-
diff --git a/library/.coveragerc b/library/.coveragerc
new file mode 100644
index 0000000..65527f4
--- /dev/null
+++ b/library/.coveragerc
@@ -0,0 +1,4 @@
+[run]
+source = bme680
+omit =
+    .tox/*
diff --git a/library/bme680/__init__.py b/library/bme680/__init__.py
index ecc4f26..62aa7ea 100644
--- a/library/bme680/__init__.py
+++ b/library/bme680/__init__.py
@@ -1,11 +1,23 @@
-from .constants import *
+"""BME680 Temperature, Pressure, Humidity & Gas Sensor."""
+from .constants import lookupTable1, lookupTable2
+from .constants import BME680Data
+from . import constants
 import math
 import time
 
 __version__ = '1.0.5'
 
+
+# Export constants to global namespace
+# so end-users can "from BME680 import NAME"
+for key in constants.__dict__:
+    value = constants.__dict__[key]
+    if key not in globals():
+        globals()[key] = value
+
+
 class BME680(BME680Data):
-    """BOSCH BME680
+    """BOSCH BME680.
 
     Gas, pressure, temperature and humidity sensor.
 
@@ -13,7 +25,14 @@ class BME680(BME680Data):
     :param i2c_device: Optional smbus or compatible instance for facilitating i2c communications.
 
     """
-    def __init__(self, i2c_addr=I2C_ADDR_PRIMARY, i2c_device=None):
+
+    def __init__(self, i2c_addr=constants.I2C_ADDR_PRIMARY, i2c_device=None):
+        """Initialise BME680 sensor instance and verify device presence.
+
+        :param i2c_addr: i2c address of BME680
+        :param i2c_device: Optional SMBus-compatible instance for i2c transport
+
+        """
         BME680Data.__init__(self)
 
         self.i2c_addr = i2c_addr
@@ -22,45 +41,46 @@ class BME680(BME680Data):
             import smbus
             self._i2c = smbus.SMBus(1)
 
-        self.chip_id = self._get_regs(CHIP_ID_ADDR, 1)
-        if self.chip_id != CHIP_ID:
-            raise RuntimeError("BME680 Not Found. Invalid CHIP ID: 0x{0:02x}".format(self.chip_id))
+        self.chip_id = self._get_regs(constants.CHIP_ID_ADDR, 1)
+        if self.chip_id != constants.CHIP_ID:
+            raise RuntimeError('BME680 Not Found. Invalid CHIP ID: 0x{0:02x}'.format(self.chip_id))
 
         self.soft_reset()
-        self.set_power_mode(SLEEP_MODE)
+        self.set_power_mode(constants.SLEEP_MODE)
 
         self._get_calibration_data()
 
-        self.set_humidity_oversample(OS_2X)
-        self.set_pressure_oversample(OS_4X)
-        self.set_temperature_oversample(OS_8X)
-        self.set_filter(FILTER_SIZE_3)
-        self.set_gas_status(ENABLE_GAS_MEAS)
+        self.set_humidity_oversample(constants.OS_2X)
+        self.set_pressure_oversample(constants.OS_4X)
+        self.set_temperature_oversample(constants.OS_8X)
+        self.set_filter(constants.FILTER_SIZE_3)
+        self.set_gas_status(constants.ENABLE_GAS_MEAS)
         self.set_temp_offset(0)
         self.get_sensor_data()
 
     def _get_calibration_data(self):
-        """Retrieves the sensor calibration data and stores it in .calibration_data"""
-        calibration = self._get_regs(COEFF_ADDR1, COEFF_ADDR1_LEN)
-        calibration += self._get_regs(COEFF_ADDR2, COEFF_ADDR2_LEN)
+        """Retrieve the sensor calibration data and store it in .calibration_data."""
+        calibration = self._get_regs(constants.COEFF_ADDR1, constants.COEFF_ADDR1_LEN)
+        calibration += self._get_regs(constants.COEFF_ADDR2, constants.COEFF_ADDR2_LEN)
 
-        heat_range = self._get_regs(ADDR_RES_HEAT_RANGE_ADDR, 1)
-        heat_value = twos_comp(self._get_regs(ADDR_RES_HEAT_VAL_ADDR, 1), bits=8)
-        sw_error = twos_comp(self._get_regs(ADDR_RANGE_SW_ERR_ADDR, 1), bits=8)
+        heat_range = self._get_regs(constants.ADDR_RES_HEAT_RANGE_ADDR, 1)
+        heat_value = constants.twos_comp(self._get_regs(constants.ADDR_RES_HEAT_VAL_ADDR, 1), bits=8)
+        sw_error = constants.twos_comp(self._get_regs(constants.ADDR_RANGE_SW_ERR_ADDR, 1), bits=8)
 
         self.calibration_data.set_from_array(calibration)
         self.calibration_data.set_other(heat_range, heat_value, sw_error)
 
     def soft_reset(self):
-        """Initiate a soft reset"""
-        self._set_regs(SOFT_RESET_ADDR, SOFT_RESET_CMD) 
-        time.sleep(RESET_PERIOD / 1000.0)
+        """Trigger a soft reset."""
+        self._set_regs(constants.SOFT_RESET_ADDR, constants.SOFT_RESET_CMD)
+        time.sleep(constants.RESET_PERIOD / 1000.0)
 
     def set_temp_offset(self, value):
-        """Set temperature offset in celsius
+        """Set temperature offset in celsius.
 
         If set, the temperature t_fine will be increased by given value in celsius.
         :param value: Temperature offset in Celsius, eg. 4, -8, 1.25
+
         """
         if value == 0:
             self.offset_temp_in_t_fine = 0
@@ -68,8 +88,8 @@ class BME680(BME680Data):
             self.offset_temp_in_t_fine = int(math.copysign((((int(abs(value) * 100)) << 8) - 128) / 5, value))
 
     def set_humidity_oversample(self, value):
-        """Set humidity oversampling
-        
+        """Set humidity oversampling.
+
         A higher oversampling value means more stable sensor readings,
         with less noise and jitter.
 
@@ -80,15 +100,15 @@ class BME680(BME680Data):
 
         """
         self.tph_settings.os_hum = value
-        self._set_bits(CONF_OS_H_ADDR, OSH_MSK, OSH_POS, value)
+        self._set_bits(constants.CONF_OS_H_ADDR, constants.OSH_MSK, constants.OSH_POS, value)
 
     def get_humidity_oversample(self):
-        """Get humidity oversampling"""
-        return (self._get_regs(CONF_OS_H_ADDR, 1) & OSH_MSK) >> OSH_POS
+        """Get humidity oversampling."""
+        return (self._get_regs(constants.CONF_OS_H_ADDR, 1) & constants.OSH_MSK) >> constants.OSH_POS
 
     def set_pressure_oversample(self, value):
-        """Set temperature oversampling
-        
+        """Set temperature oversampling.
+
         A higher oversampling value means more stable sensor readings,
         with less noise and jitter.
 
@@ -96,18 +116,18 @@ class BME680(BME680Data):
         causing a slower response time to fast transients.
 
         :param value: Oversampling value, one of: OS_NONE, OS_1X, OS_2X, OS_4X, OS_8X, OS_16X
-        
+
         """
         self.tph_settings.os_pres = value
-        self._set_bits(CONF_T_P_MODE_ADDR, OSP_MSK, OSP_POS, value)
+        self._set_bits(constants.CONF_T_P_MODE_ADDR, constants.OSP_MSK, constants.OSP_POS, value)
 
     def get_pressure_oversample(self):
-        """Get pressure oversampling"""
-        return (self._get_regs(CONF_T_P_MODE_ADDR, 1) & OSP_MSK) >> OSP_POS
+        """Get pressure oversampling."""
+        return (self._get_regs(constants.CONF_T_P_MODE_ADDR, 1) & constants.OSP_MSK) >> constants.OSP_POS
 
     def set_temperature_oversample(self, value):
-        """Set pressure oversampling
-        
+        """Set pressure oversampling.
+
         A higher oversampling value means more stable sensor readings,
         with less noise and jitter.
 
@@ -115,18 +135,18 @@ class BME680(BME680Data):
         causing a slower response time to fast transients.
 
         :param value: Oversampling value, one of: OS_NONE, OS_1X, OS_2X, OS_4X, OS_8X, OS_16X
-        
+
         """
         self.tph_settings.os_temp = value
-        self._set_bits(CONF_T_P_MODE_ADDR, OST_MSK, OST_POS, value)
+        self._set_bits(constants.CONF_T_P_MODE_ADDR, constants.OST_MSK, constants.OST_POS, value)
 
     def get_temperature_oversample(self):
-        """Get temperature oversampling"""
-        return (self._get_regs(CONF_T_P_MODE_ADDR, 1) & OST_MSK) >> OST_POS
+        """Get temperature oversampling."""
+        return (self._get_regs(constants.CONF_T_P_MODE_ADDR, 1) & constants.OST_MSK) >> constants.OST_POS
 
     def set_filter(self, value):
-        """Set IIR filter size
-        
+        """Set IIR filter size.
+
         Optionally remove short term fluctuations from the temperature and pressure readings,
         increasing their resolution but reducing their bandwidth.
 
@@ -138,40 +158,42 @@ class BME680(BME680Data):
 
         """
         self.tph_settings.filter = value
-        self._set_bits(CONF_ODR_FILT_ADDR, FILTER_MSK, FILTER_POS, value)
+        self._set_bits(constants.CONF_ODR_FILT_ADDR, constants.FILTER_MSK, constants.FILTER_POS, value)
 
     def get_filter(self):
-        """Get filter size"""
-        return (self._get_regs(CONF_ODR_FILT_ADDR, 1) & FILTER_MSK) >> FILTER_POS
+        """Get filter size."""
+        return (self._get_regs(constants.CONF_ODR_FILT_ADDR, 1) & constants.FILTER_MSK) >> constants.FILTER_POS
 
     def select_gas_heater_profile(self, value):
-        """Set current gas sensor conversion profile: 0 to 9
-        
+        """Set current gas sensor conversion profile.
+
         Select one of the 10 configured heating durations/set points.
-        
+
+        :param value: Profile index from 0 to 9
+
         """
-        if value > NBCONV_MAX or value < NBCONV_MIN:
-            raise ValueError("Profile '{}' should be between {} and {}".format(value, NBCONV_MIN, NBCONV_MAX))
+        if value > constants.NBCONV_MAX or value < constants.NBCONV_MIN:
+            raise ValueError("Profile '{}' should be between {} and {}".format(value, constants.NBCONV_MIN, constants.NBCONV_MAX))
 
         self.gas_settings.nb_conv = value
-        self._set_bits(CONF_ODR_RUN_GAS_NBC_ADDR, NBCONV_MSK, NBCONV_POS, value)
+        self._set_bits(constants.CONF_ODR_RUN_GAS_NBC_ADDR, constants.NBCONV_MSK, constants.NBCONV_POS, value)
 
     def get_gas_heater_profile(self):
-        """Get gas sensor conversion profile: 0 to 9"""
-        return self._get_regs(CONF_ODR_RUN_GAS_NBC_ADDR, 1) & NBCONV_MSK
+        """Get gas sensor conversion profile: 0 to 9."""
+        return self._get_regs(constants.CONF_ODR_RUN_GAS_NBC_ADDR, 1) & constants.NBCONV_MSK
 
     def set_gas_status(self, value):
-        """Enable/disable gas sensor"""
+        """Enable/disable gas sensor."""
         self.gas_settings.run_gas = value
-        self._set_bits(CONF_ODR_RUN_GAS_NBC_ADDR, RUN_GAS_MSK, RUN_GAS_POS, value)
+        self._set_bits(constants.CONF_ODR_RUN_GAS_NBC_ADDR, constants.RUN_GAS_MSK, constants.RUN_GAS_POS, value)
 
     def get_gas_status(self):
-        """Get the current gas status"""
-        return (self._get_regs(CONF_ODR_RUN_GAS_NBC_ADDR, 1) & RUN_GAS_MSK) >> RUN_GAS_POS
+        """Get the current gas status."""
+        return (self._get_regs(constants.CONF_ODR_RUN_GAS_NBC_ADDR, 1) & constants.RUN_GAS_MSK) >> constants.RUN_GAS_POS
 
     def set_gas_heater_profile(self, temperature, duration, nb_profile=0):
-        """Set temperature and duration of gas sensor heater
-        
+        """Set temperature and duration of gas sensor heater.
+
         :param temperature: Target temperature in degrees celsius, between 200 and 400
         :param durarion: Target duration in milliseconds, between 1 and 4032
         :param nb_profile: Target profile, between 0 and 9
@@ -181,23 +203,23 @@ class BME680(BME680Data):
         self.set_gas_heater_duration(duration, nb_profile=nb_profile)
 
     def set_gas_heater_temperature(self, value, nb_profile=0):
-        """Set gas sensor heater temperature
+        """Set gas sensor heater temperature.
 
         :param value: Target temperature in degrees celsius, between 200 and 400
-        
+
         When setting an nb_profile other than 0,
         make sure to select it with select_gas_heater_profile.
 
         """
-        if nb_profile > NBCONV_MAX or value < NBCONV_MIN:
-            raise ValueError("Profile '{}' should be between {} and {}".format(nb_profile, NBCONV_MIN, NBCONV_MAX))
+        if nb_profile > constants.NBCONV_MAX or value < constants.NBCONV_MIN:
+            raise ValueError('Profile "{}" should be between {} and {}'.format(nb_profile, constants.NBCONV_MIN, constants.NBCONV_MAX))
 
         self.gas_settings.heatr_temp = value
         temp = int(self._calc_heater_resistance(self.gas_settings.heatr_temp))
-        self._set_regs(RES_HEAT0_ADDR + nb_profile, temp)
+        self._set_regs(constants.RES_HEAT0_ADDR + nb_profile, temp)
 
     def set_gas_heater_duration(self, value, nb_profile=0):
-        """Set gas sensor heater duration
+        """Set gas sensor heater duration.
 
         Heating durations between 1 ms and 4032 ms can be configured.
         Approximately 20-30 ms are necessary for the heater to reach the intended target temperature.
@@ -206,68 +228,68 @@ class BME680(BME680Data):
 
         When setting an nb_profile other than 0,
         make sure to select it with select_gas_heater_profile.
-        
+
         """
-        if nb_profile > NBCONV_MAX or value < NBCONV_MIN:
-            raise ValueError("Profile '{}' should be between {} and {}".format(nb_profile, NBCONV_MIN, NBCONV_MAX))
+        if nb_profile > constants.NBCONV_MAX or value < constants.NBCONV_MIN:
+            raise ValueError('Profile "{}" should be between {} and {}'.format(nb_profile, constants.NBCONV_MIN, constants.NBCONV_MAX))
 
         self.gas_settings.heatr_dur = value
         temp = self._calc_heater_duration(self.gas_settings.heatr_dur)
-        self._set_regs(GAS_WAIT0_ADDR + nb_profile, temp)
+        self._set_regs(constants.GAS_WAIT0_ADDR + nb_profile, temp)
 
     def set_power_mode(self, value, blocking=True):
-        """Set power mode"""
-        if value not in (SLEEP_MODE, FORCED_MODE):
-            print("Power mode should be one of SLEEP_MODE or FORCED_MODE")
+        """Set power mode."""
+        if value not in (constants.SLEEP_MODE, constants.FORCED_MODE):
+            raise ValueError('Power mode should be one of SLEEP_MODE or FORCED_MODE')
 
         self.power_mode = value
 
-        self._set_bits(CONF_T_P_MODE_ADDR, MODE_MSK, MODE_POS, value)
+        self._set_bits(constants.CONF_T_P_MODE_ADDR, constants.MODE_MSK, constants.MODE_POS, value)
 
         while blocking and self.get_power_mode() != self.power_mode:
-            time.sleep(POLL_PERIOD_MS / 1000.0)
+            time.sleep(constants.POLL_PERIOD_MS / 1000.0)
 
     def get_power_mode(self):
-        """Get power mode"""
-        self.power_mode = self._get_regs(CONF_T_P_MODE_ADDR, 1)
+        """Get power mode."""
+        self.power_mode = self._get_regs(constants.CONF_T_P_MODE_ADDR, 1)
         return self.power_mode
 
     def get_sensor_data(self):
         """Get sensor data.
-        
+
         Stores data in .data and returns True upon success.
 
         """
-        self.set_power_mode(FORCED_MODE)
+        self.set_power_mode(constants.FORCED_MODE)
 
         for attempt in range(10):
-            status = self._get_regs(FIELD0_ADDR, 1)
+            status = self._get_regs(constants.FIELD0_ADDR, 1)
 
-            if (status & NEW_DATA_MSK) == 0:
-                time.sleep(POLL_PERIOD_MS / 1000.0)
+            if (status & constants.NEW_DATA_MSK) == 0:
+                time.sleep(constants.POLL_PERIOD_MS / 1000.0)
                 continue
 
-            regs = self._get_regs(FIELD0_ADDR, FIELD_LENGTH)
+            regs = self._get_regs(constants.FIELD0_ADDR, constants.FIELD_LENGTH)
 
-            self.data.status = regs[0] & NEW_DATA_MSK
+            self.data.status = regs[0] & constants.NEW_DATA_MSK
             # Contains the nb_profile used to obtain the current measurement
-            self.data.gas_index = regs[0] & GAS_INDEX_MSK
+            self.data.gas_index = regs[0] & constants.GAS_INDEX_MSK
             self.data.meas_index = regs[1]
 
             adc_pres = (regs[2] << 12) | (regs[3] << 4) | (regs[4] >> 4)
             adc_temp = (regs[5] << 12) | (regs[6] << 4) | (regs[7] >> 4)
             adc_hum = (regs[8] << 8) | regs[9]
             adc_gas_res = (regs[13] << 2) | (regs[14] >> 6)
-            gas_range = regs[14] & GAS_RANGE_MSK
+            gas_range = regs[14] & constants.GAS_RANGE_MSK
 
-            self.data.status |= regs[14] & GASM_VALID_MSK
-            self.data.status |= regs[14] & HEAT_STAB_MSK
+            self.data.status |= regs[14] & constants.GASM_VALID_MSK
+            self.data.status |= regs[14] & constants.HEAT_STAB_MSK
 
-            self.data.heat_stable = (self.data.status & HEAT_STAB_MSK) > 0
+            self.data.heat_stable = (self.data.status & constants.HEAT_STAB_MSK) > 0
 
             temperature = self._calc_temperature(adc_temp)
             self.data.temperature = temperature / 100.0
-            self.ambient_temperature = temperature # Saved for heater calc
+            self.ambient_temperature = temperature  # Saved for heater calc
 
             self.data.pressure = self._calc_pressure(adc_pres) / 100.0
             self.data.humidity = self._calc_humidity(adc_hum) / 1000.0
@@ -277,27 +299,28 @@ class BME680(BME680Data):
         return False
 
     def _set_bits(self, register, mask, position, value):
-        """Mask out and set one or more bits in a register"""
+        """Mask out and set one or more bits in a register."""
         temp = self._get_regs(register, 1)
         temp &= ~mask
         temp |= value << position
         self._set_regs(register, temp)
 
     def _set_regs(self, register, value):
-        """Set one or more registers"""
+        """Set one or more registers."""
         if isinstance(value, int):
             self._i2c.write_byte_data(self.i2c_addr, register, value)
         else:
             self._i2c.write_i2c_block_data(self.i2c_addr, register, value)
 
     def _get_regs(self, register, length):
-        """Get one or more registers"""
+        """Get one or more registers."""
         if length == 1:
             return self._i2c.read_byte_data(self.i2c_addr, register)
         else:
             return self._i2c.read_i2c_block_data(self.i2c_addr, register, length)
-        
+
     def _calc_temperature(self, temperature_adc):
+        """Convert the raw temperature to degrees C using calibration_data."""
         var1 = (temperature_adc >> 3) - (self.calibration_data.par_t1 << 1)
         var2 = (var1 * self.calibration_data.par_t2) >> 11
         var3 = ((var1 >> 1) * (var1 >> 1)) >> 12
@@ -310,12 +333,13 @@ class BME680(BME680Data):
         return calc_temp
 
     def _calc_pressure(self, pressure_adc):
+        """Convert the raw pressure using calibration data."""
         var1 = ((self.calibration_data.t_fine) >> 1) - 64000
         var2 = ((((var1 >> 2) * (var1 >> 2)) >> 11) *
-            self.calibration_data.par_p6) >> 2
+                self.calibration_data.par_p6) >> 2
         var2 = var2 + ((var1 * self.calibration_data.par_p5) << 1)
         var2 = (var2 >> 2) + (self.calibration_data.par_p4 << 16)
-        var1 = (((((var1 >> 2) * (var1 >> 2)) >> 13 ) *
+        var1 = (((((var1 >> 2) * (var1 >> 2)) >> 13) *
                 ((self.calibration_data.par_p3 << 5)) >> 3) +
                 ((self.calibration_data.par_p2 * var1) >> 1))
         var1 = var1 >> 18
@@ -330,26 +354,27 @@ class BME680(BME680Data):
             calc_pressure = ((calc_pressure << 1) // var1)
 
         var1 = (self.calibration_data.par_p9 * (((calc_pressure >> 3) *
-            (calc_pressure >> 3)) >> 13)) >> 12
+                (calc_pressure >> 3)) >> 13)) >> 12
         var2 = ((calc_pressure >> 2) *
-            self.calibration_data.par_p8) >> 13
+                self.calibration_data.par_p8) >> 13
         var3 = ((calc_pressure >> 8) * (calc_pressure >> 8) *
-            (calc_pressure >> 8) *
-            self.calibration_data.par_p10) >> 17
+                (calc_pressure >> 8) *
+                self.calibration_data.par_p10) >> 17
 
         calc_pressure = (calc_pressure) + ((var1 + var2 + var3 +
-            (self.calibration_data.par_p7 << 7)) >> 4)
+                                           (self.calibration_data.par_p7 << 7)) >> 4)
 
         return calc_pressure
 
     def _calc_humidity(self, humidity_adc):
+        """Convert the raw humidity using calibration data."""
         temp_scaled = ((self.calibration_data.t_fine * 5) + 128) >> 8
-        var1 = (humidity_adc - ((self.calibration_data.par_h1 * 16))) \
-                - (((temp_scaled * self.calibration_data.par_h3) // (100)) >> 1)
-        var2 = (self.calibration_data.par_h2
-                * (((temp_scaled * self.calibration_data.par_h4) // (100))
-                + (((temp_scaled * ((temp_scaled * self.calibration_data.par_h5) // (100))) >> 6)
-                // (100)) + (1 * 16384))) >> 10
+        var1 = (humidity_adc - ((self.calibration_data.par_h1 * 16))) -\
+               (((temp_scaled * self.calibration_data.par_h3) // (100)) >> 1)
+        var2 = (self.calibration_data.par_h2 *
+                (((temp_scaled * self.calibration_data.par_h4) // (100)) +
+                 (((temp_scaled * ((temp_scaled * self.calibration_data.par_h5) // (100))) >> 6) //
+                 (100)) + (1 * 16384))) >> 10
         var3 = var1 * var2
         var4 = self.calibration_data.par_h6 << 7
         var4 = ((var4) + ((temp_scaled * self.calibration_data.par_h7) // (100))) >> 4
@@ -357,21 +382,23 @@ class BME680(BME680Data):
         var6 = (var4 * var5) >> 1
         calc_hum = (((var3 + var6) >> 10) * (1000)) >> 12
 
-        return min(max(calc_hum,0),100000)
+        return min(max(calc_hum, 0), 100000)
 
     def _calc_gas_resistance(self, gas_res_adc, gas_range):
+        """Convert the raw gas resistance using calibration data."""
         var1 = ((1340 + (5 * self.calibration_data.range_sw_err)) * (lookupTable1[gas_range])) >> 16
         var2 = (((gas_res_adc << 15) - (16777216)) + var1)
         var3 = ((lookupTable2[gas_range] * var1) >> 9)
         calc_gas_res = ((var3 + (var2 >> 1)) / var2)
 
         if calc_gas_res < 0:
-            calc_gas_res = (1<<32) + calc_gas_res
+            calc_gas_res = (1 << 32) + calc_gas_res
 
         return calc_gas_res
 
     def _calc_heater_resistance(self, temperature):
-        temperature = min(max(temperature,200),400)
+        """Convert raw heater resistance using calibration data."""
+        temperature = min(max(temperature, 200), 400)
 
         var1 = ((self.ambient_temperature * self.calibration_data.par_gh3) / 1000) * 256
         var2 = (self.calibration_data.par_gh1 + 784) * (((((self.calibration_data.par_gh2 + 154009) * temperature * 5) / 100) + 3276800) / 10)
@@ -384,6 +411,7 @@ class BME680(BME680Data):
         return heatr_res
 
     def _calc_heater_duration(self, duration):
+        """Calculate correct value for heater duration setting from milliseconds."""
         if duration < 0xfc0:
             factor = 0
 
diff --git a/library/bme680/constants.py b/library/bme680/constants.py
index 5cc0840..5033acc 100644
--- a/library/bme680/constants.py
+++ b/library/bme680/constants.py
@@ -1,3 +1,5 @@
+"""BME680 constants, structures and utilities."""
+
 # BME680 General config
 POLL_PERIOD_MS = 10
 
@@ -118,7 +120,7 @@ TMP_BUFFER_LENGTH = 40
 REG_BUFFER_LENGTH = 6
 FIELD_DATA_LENGTH = 3
 GAS_REG_BUF_LENGTH = 20
-GAS_HEATER_PROF_LEN_MAX  = 10
+GAS_HEATER_PROF_LEN_MAX = 10
 
 # Settings selector
 OST_SEL = 1
@@ -133,7 +135,7 @@ GAS_SENSOR_SEL = GAS_MEAS_SEL | RUN_GAS_SEL | NBCONV_SEL
 
 # Number of conversion settings
 NBCONV_MIN = 0
-NBCONV_MAX = 9 # Was 10, but there are only 10 settings: 0 1 2 ... 8 9
+NBCONV_MAX = 9  # Was 10, but there are only 10 settings: 0 1 2 ... 8 9
 
 # Mask definitions
 GAS_MEAS_MSK = 0x30
@@ -214,30 +216,37 @@ REG_HCTRL_INDEX = 0
 
 # Look up tables for the possible gas range values
 lookupTable1 = [2147483647, 2147483647, 2147483647, 2147483647,
-        2147483647, 2126008810, 2147483647, 2130303777, 2147483647,
-        2147483647, 2143188679, 2136746228, 2147483647, 2126008810,
-        2147483647, 2147483647]
+                2147483647, 2126008810, 2147483647, 2130303777, 2147483647,
+                2147483647, 2143188679, 2136746228, 2147483647, 2126008810,
+                2147483647, 2147483647]
 
 lookupTable2 = [4096000000, 2048000000, 1024000000, 512000000,
-        255744255, 127110228, 64000000, 32258064,
-        16016016, 8000000, 4000000, 2000000,
-        1000000, 500000, 250000, 125000]
+                255744255, 127110228, 64000000, 32258064,
+                16016016, 8000000, 4000000, 2000000,
+                1000000, 500000, 250000, 125000]
+
 
 def bytes_to_word(msb, lsb, bits=16, signed=False):
+    """Convert a most and least significant byte into a word."""
+    # TODO: Reimpliment with struct
     word = (msb << 8) | lsb
     if signed:
         word = twos_comp(word, bits)
     return word
 
+
 def twos_comp(val, bits=16):
+    """Convert two bytes into a two's compliment signed word."""
+    # TODO: Reimpliment with struct
     if val & (1 << (bits - 1)) != 0:
         val = val - (1 << bits)
     return val
 
-# Sensor field data structure
 
 class FieldData:
-    def __init__(self):
+    """Structure for storing BME680 sensor data."""
+
+    def __init__(self):  # noqa D107
         # Contains new_data, gasm_valid & heat_stab
         self.status = None
         self.heat_stable = False
@@ -254,10 +263,11 @@ class FieldData:
         # Gas resistance in Ohms
         self.gas_resistance = None
 
-# Structure to hold the Calibration data
 
 class CalibrationData:
-    def __init__(self):
+    """Structure for storing BME680 calibration data."""
+
+    def __init__(self):  # noqa D107
         self.par_h1 = None
         self.par_h2 = None
         self.par_h3 = None
@@ -291,6 +301,7 @@ class CalibrationData:
         self.range_sw_err = None
 
     def set_from_array(self, calibration):
+        """Set paramaters from an array of bytes."""
         # Temperature related coefficients
         self.par_t1 = bytes_to_word(calibration[T1_MSB_REG], calibration[T1_LSB_REG])
         self.par_t2 = bytes_to_word(calibration[T2_MSB_REG], calibration[T2_LSB_REG], bits=16, signed=True)
@@ -323,15 +334,20 @@ class CalibrationData:
         self.par_gh3 = twos_comp(calibration[GH3_REG], bits=8)
 
     def set_other(self, heat_range, heat_value, sw_error):
+        """Set other values."""
         self.res_heat_range = (heat_range & RHRANGE_MSK) // 16
         self.res_heat_val = heat_value
         self.range_sw_err = (sw_error & RSERROR_MSK) // 16
 
-# BME680 sensor settings structure which comprises of ODR,
-# over-sampling and filter settings.
 
 class TPHSettings:
-    def __init__(self):
+    """Structure for storing BME680 sensor settings.
+
+    Comprises of output data rate, over-sampling and filter settings.
+
+    """
+
+    def __init__(self):  # noqa D107
         # Humidity oversampling
         self.os_hum = None
         # Temperature oversampling
@@ -341,11 +357,11 @@ class TPHSettings:
         # Filter coefficient
         self.filter = None
 
-# BME680 gas sensor which comprises of gas settings
-## and status parameters
 
 class GasSettings:
-    def __init__(self):
+    """Structure for storing BME680 gas settings and status."""
+
+    def __init__(self):  # noqa D107
         # Variable to store nb conversion
         self.nb_conv = None
         # Variable to store heater control
@@ -357,10 +373,11 @@ class GasSettings:
         # Pointer to store duration profile
         self.heatr_dur = None
 
-# BME680 device structure
 
 class BME680Data:
-    def __init__(self):
+    """Structure to represent BME680 device."""
+
+    def __init__(self):  # noqa D107
         # Chip Id
         self.chip_id = None
         # Device Id
diff --git a/library/setup.cfg b/library/setup.cfg
new file mode 100644
index 0000000..81dc0bf
--- /dev/null
+++ b/library/setup.cfg
@@ -0,0 +1,14 @@
+[flake8]
+exclude =
+	test.py
+	.tox
+	.eggs
+	.git
+	__pycache__
+	build
+	dist
+	tests
+ignore =
+	E501
+	F403
+	F405
diff --git a/library/setup.py b/library/setup.py
index b47bfce..f40026b 100755
--- a/library/setup.py
+++ b/library/setup.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 
 """
-Copyright (c) 2016 Pimoroni
+Copyright (c) 2016 Pimoroni.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of
 this software and associated documentation files (the "Software"), to deal in
@@ -38,17 +38,17 @@ classifiers = ['Development Status :: 5 - Production/Stable',
                'Topic :: System :: Hardware']
 
 setup(
-    name            = 'bme680',
-    version         = '1.0.5',
-    author          = 'Philip Howard',
-    author_email    = 'phil@pimoroni.com',
-    description     = """Python library for driving the Pimoroni BME680 Breakout""",
-    long_description= open('README.rst').read() + "\n" + open('CHANGELOG.txt').read(),
-    license         = 'MIT',
-    keywords        = 'Raspberry Pi',
-    url             = 'http://www.pimoroni.com',
-    classifiers     = classifiers,
-    packages        = ['bme680'],
-    py_modules      = [],
-    install_requires= []
+    name='bme680',
+    version='1.0.5',
+    author='Philip Howard',
+    author_email='phil@pimoroni.com',
+    description="""Python library for driving the Pimoroni BME680 Breakout""",
+    long_description=open('README.rst').read() + '\n' + open('CHANGELOG.txt').read(),
+    license='MIT',
+    keywords='Raspberry Pi',
+    url='http://www.pimoroni.com',
+    classifiers=classifiers,
+    packages=['bme680'],
+    py_modules=[],
+    install_requires=[]
 )
diff --git a/library/tests/setup.cfg b/library/tests/setup.cfg
new file mode 100644
index 0000000..23a30f5
--- /dev/null
+++ b/library/tests/setup.cfg
@@ -0,0 +1,8 @@
+[flake8]
+exclude =
+	__pycache__
+ignore =
+    D100 # Do not require docstrings
+	E501
+	F403
+	F405
\ No newline at end of file
diff --git a/library/tests/test_setup.py b/library/tests/test_setup.py
new file mode 100644
index 0000000..95b7391
--- /dev/null
+++ b/library/tests/test_setup.py
@@ -0,0 +1,57 @@
+import sys
+import mock
+import pytest
+import bme680
+
+
+class MockSMBus:
+    """Mock a basic non-presence SMBus device to cause BME680 to fail.
+
+    Returns 0 in all cases, so that CHIP_ID will never match.
+
+    """
+
+    def __init__(self, bus):  # noqa D107
+        pass
+
+    def read_byte_data(self, addr, register):
+        """Return 0 for all read attempts."""
+        return 0
+
+
+class MockSMBusPresent:
+    """Mock enough of the BME680 for the library to initialise and test."""
+
+    def __init__(self, bus):
+        """Initialise with test data."""
+        self.regs = [0 for _ in range(256)]
+        self.regs[bme680.CHIP_ID_ADDR] = bme680.CHIP_ID
+
+    def read_byte_data(self, addr, register):
+        """Read a single byte from fake registers."""
+        return self.regs[register]
+
+    def write_byte_data(self, addr, register, value):
+        """Write a single byte to fake registers."""
+        self.regs[register] = value
+
+    def read_i2c_block_data(self, addr, register, length):
+        """Read up to length bytes from register."""
+        return self.regs[register:register + length]
+
+
+def test_setup_not_present():
+    """Mock the adbsence of a BME680 and test initialisation."""
+    sys.modules['smbus'] = mock.MagicMock()
+    sys.modules['smbus'].SMBus = MockSMBus
+
+    with pytest.raises(RuntimeError):
+        sensor = bme680.BME680()  # noqa F841
+
+
+def test_setup_mock_present():
+    """Mock the presence of a BME680 and test initialisation."""
+    sys.modules['smbus'] = mock.MagicMock()
+    sys.modules['smbus'].SMBus = MockSMBusPresent
+
+    sensor = bme680.BME680()  # noqa F841
diff --git a/library/tox.ini b/library/tox.ini
new file mode 100644
index 0000000..89947cb
--- /dev/null
+++ b/library/tox.ini
@@ -0,0 +1,25 @@
+[tox]
+envlist = py{27,35},qa
+skip_missing_interpreters = True
+
+[testenv]
+commands =
+	python setup.py install
+	coverage run -m py.test -v -r wsx
+	coverage report
+deps =
+	mock
+	pytest>=3.1
+	pytest-cov
+ 
+[testenv:qa]
+commands =
+	flake8
+	flake8 tests/
+	flake8 ../examples/
+	rstcheck README.rst
+deps =
+	flake8
+	flake8-docstrings
+	flake8-quotes
+	rstcheck