do not crash when SHT sensor library is missing

sensors.py

@@ -4,12 +4,21 @@ from collections import deque
 import re
 from os.path import exists
 
+try:
     import RPi.GPIO as GPIO
     GPIO.setmode(GPIO.BCM)
+    rpi = True
+except:
+    rpi = False
 
+try:
     # SHT40
     import board
     import adafruit_sht4x
+    enable_sht = True
+except:
+    print("Adafruit SHT4X not available!")
+    enable_sht = False
 
 # TODO client: add a way to disable live plotting? server: stop
 # sending data periodically to everybody!
@@ -39,7 +48,8 @@ class GPIOState(Sensor):
         try:
             self.value = GPIO.input(self.pin)
         except:
-            self.value = None
+            print(f"Could not read pin {self.pin}")
+            self.value = 0
         self.time = perf_counter()
         
         return (self.time, self.transform(self.value))
@@ -67,27 +77,53 @@ class Temperature1W(Sensor):
             return (time, None)
         return (time, int(re.search("t=([0-9]+)", content[1]).group(1)) / 1000.0)
 
+if enable_sht:
+    i2c = board.I2C()  # uses board.SCL and board.SDA
+    sht = adafruit_sht4x.SHT4x(i2c)
+    print('Serial: ', hex(sht.serial_number))
+    SHT40_DEFAULT = adafruit_sht4x.Mode.NOHEAT_HIGHPRECISION
+    sht.mode = SHT40_DEFAULT
+
 class SHT40(Sensor):
-    def __init__(self, what):
+    def __init__(self, what, every=60):
+        if what not in ("Temperature", "Humidity"):
+            print("ERROR: invalid sensor value: ", what)
+            return
         self.measure = what
-        self.i2c = board.I2C()  # uses board.SCL and board.SDA
-        self.sht = adafruit_sht4x.SHT4x(i2c)
-        print('Serial: ', hex(self.sht.serial_number))
-        # FIXME:
-        self.sht.mode = adafruit_sht4x.Mode.NOHEAT_HIGHPRECISION
+        if not enable_sht:
+            return
+        self.heat_every = every
+        if self.measure != "Temperature":
+            self.last_heat = perf_counter()
+        self.heatmode = adafruit_sht4x.Mode.HIGHHEAT_1S
+        self.standardmode = SHT40_DEFAULT
+        # mode: adafruit_sht4x.Mode.string[sht.mode]
         # Can also set the mode to enable heater
         # sht.mode = adafruit_sht4x.Mode.LOWHEAT_100MS
         # modes = [adafruit_sht4x.Mode.HIGHHEAT_1S,
         #          adafruit_sht4x.Mode.LOWHEAT_100MS,
         #          adafruit_sht4x.Mode.NOHEAT_HIGHPRECISION]
+    def is_temperature(self):
+        return self.measure == "Temperature"
+
+    def is_humidity(self):
+        return self.measure == "Humidity"
+
+    def reset_mode(self):
+        sht.mode = self.standardmode
 
     def read(self):
         time = perf_counter()
+        reset = False
+        if self.is_humidity():
+            timediff = time - self.last_heat
+            if timediff > self.heat_every:
+                reset = True
+                sht.mode = self.heatmode
         temperature, relative_humidity = sht.measurements
-        # print("Temperature: %0.1f C" % temperature)
-        # print("Humidity: %0.1f %%" % (relative_humidity))
-        # print("")
-        return (time, temerature if self.measure == 'Temperature' else relative_humidityg)
+        if reset:
+            self.reset_mode()
+        return (time, temperature if self.measure == 'Temperature' else relative_humidity)
 
 class Sensors():
     def __init__(self, history=2621440):
@@ -102,6 +138,9 @@ class Sensors():
 
     "Scan for new sensors"
     def scan(self):
+        # Read something like this from a stored prefs json
+        # sensors_names_map = {}
+        # Then, scan, apply existing names and use placholders for new sensors
         # FIXME: should scan, apply stored data and return this
         self.available_sensors = {
             'T_food':     Temperature1W('28-06214252b671'),
@@ -123,8 +162,11 @@ class Sensors():
 
     def read(self):
         for sensor in self.available_sensors.keys():
+            try:
                 time, value = self.available_sensors[sensor].read()
                 self.values[sensor] = (str(self.perf_datetime(time)), value)
+            except Exception as e:
+                print("Error reading sensors", sensor, ": ", e)
         self.history.append(self.value_tuple())
 
     def get_sensor_value(self, sensor_name):