DHT22.py sample code returns: AttributeError: 'NoneType' object has no attribute 'send' about pigpio HOT 3 CLOSED

Leave the class as it originally was but remove the import atexit and the atexit call.

Change the main to look like the following.

   import pigpio

   import DHT22

   pi = pigpio.pi()

   s = DHT22.sensor(pi, 4)

   s.trigger()

   time.sleep(0.2)

   print("{} {} {:3.2f} {} {} {} {}".format(
      s.humidity(), s.temperature(), s.staleness(),
      s.bad_checksum(), s.short_message(), s.missing_message(),
      s.sensor_resets()))

   s.cancel()

   pi.stop()

The reading will be good provided bad_checksum(), short_message(), missing_message(), and
sensor_resets() are all zero.

from pigpio.

That resolved the problem. Thank you!

Is the atexit code a safety mechanism to ensure that cancel is always
performed?

What would happen if the program exited without calling cancel?

Also, I have noticed that on my gen 1 Pi model B that pigpiod always uses
around 8% CPU as reported by TOP.

Is that normal?

On Tue, Jul 28, 2015 at 5:30 PM, joan2937 [email protected] wrote:

Leave the class as it originally was but remove the import atexit and the
atexit call.

Change the main to look like the following.

import pigpio

import DHT22

pi = pigpio.pi()

s = DHT22.sensor(pi, 4)

s.trigger()

time.sleep(0.2)

print("{} {} {:3.2f} {} {} {} {}".format(
s.humidity(), s.temperature(), s.staleness(),
s.bad_checksum(), s.short_message(), s.missing_message(),
s.sensor_resets()))

s.cancel()

pi.stop()

The reading will be good provided bad_checksum(), short_message(),
missing_message(), and
sensor_resets() are all zero.

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#16 (comment).

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The atexit in the class was really to make sure the watchdog was switched off if the main program terminated (the expectation being that most often the class would be used in a forever loop). If the watchdog was left switched on it might confuse a later script which just expected to get level changes.

8% CPU usage is about right on a non-Pi2. That's the base level for the overhead of the 200 thousand gpio reads per second made by the daemon. However that's a fixed overhead regardless of how many gpios are used for PWM or servo pulses and is very quickly more efficient than trying to service anywhere near that number of gpio interrupts.

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