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Multipurpose sensor handler, read sensor & do somethings (send, save, trigger, ...) with the value.

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Multipurpose sensor handler, read sensor & do somethings (send, save, trigger, ...) with the value.


pip install pondslider


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What is pondslider

The pondslider is a python module to read sensor values by Sensor handler, and do somethins with the value by Value handler.

What is pondslider for?

The pondslider is for making sensor application quickly by reusing existing codes.

  • Reusing existing Sensor reading code through unified interface provided by Sensor handler mention later.
  • Reusing existing Value handling code through unified interface provided by Value handler mention later.

How the pondslider work?

First, the pondslider read a configration file to specify:

  • Which sensors shoul be read.
  • Which values are returned by specific sensor.
  • What shoud it do for each value.

Then, pondslider get sensor values through specific sensor handlers, and call value handlers which is related.

What is Sensor handler?

The Sensor handler is a python module which wrap existing sensor reading code having various interface, to provide unified interface as follows:

  • unified read() function: Sensor handler unifies various function call of sensor value reading on the existing codes as read()

  • well-formed return value: The read() function return a python dictionally of name and value pairs as follow:

{'humiditydeficit': 15.9, 'temp': 26.8, 'humidity': 37.6}

Thankfully, there are huge open source code base written by capable and benign engineers on the github, pypi and other repositories. In my experience, it' very rare to face a situation of the necessity of writing a code to readi a sensor value myself, insted I can find reusable code of most sensors easily and use it gratefully. But also there are wide variety of the interface of these code and form of result, so I just need to make wrapper code to adapt interface. The Sensor handler is just these code of wrapping these pre-existing valuable code to provide unified interface.

Typically, a sensor handler is created as a wrapper module of exising python module with import and call there function to read sensor value as follow:

# import existing module
import SomethingExistingSensorModule

# unified read() interface

def read():
  # prepare existing module
  a_sensor =

  # call there function to read sensor value 
  values   = a_sensor.there_func_to_read_sensor()

  # re-format to name-value pair.
  return adjust_the_format(values)

def adjust_the_format(value)
  ''' adjst the format of value as a dictionaly of name & value pair. '''

In other case, with external executable file,

# import python standard external executable handle module
import subprocess

def read():

  # call external executable and get return strings
  p = subprocess.Popen("./SomethingExistingExecutable2GetSensorValue",
  std_out, std_err = p.communicate(None, timeout=20)
  value = std_out.strip()

  # re-format to name-value pair.
  return adjust_the_format(value)

def adjust_the_format(value)
  ''' adjst the format of value as a dictionaly of name & value pair. '''

Of cource, It's OK to make Sensor handler as reading sensor value directory.

import serial

def read():
  # mh-z19 CO2 sensor
    ser = serial.Serial(serial_dev,
    while 1:
      if len(s) >= 4 and s[0] == "\xff" and s[1] == "\x86":
        return {'co2': ord(s[2])*256 + ord(s[3])}

What is Value handler?

The Value handler is a python module which recieve sensor value, and do something with it, for example, send to server, write to strage, and so on. The purpose of valule handler is to provide a unified interface to handle acquired sensor value with following interface:

def handle(sensor_hander, data_name, value):

example handlers

example of handlers are available at


pip install pondslider


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How to set Sensor and Value handlers

There are 2 way to set handers. One is to use command-line option, the other is TOML formatted config file. In case both config and command-line option is set, the pondslider handle also both in the order config file first, then command-line.

For the way to specify a various handlers in the various package & directory, please refer "How to specify a handler package in the various package & directory hierarchies".

Set Sensor and Value handlers by command-line option

The Sensor handlers can be set by command-line option --sensor_handlers. This is list type command-line option, you can specify nesessary sensor handlers module like mh-z19 and dht22 as follows:

--sensor_handlers mh_z19 dht22

For the value handlers also has similar command-line option --value_handlers. For example, spesify modules of sender.monitor.send and as follows:

--value_handlers sender.monitor.send

Each value handlers handle() functions is called with All value red from All Sensor handlers. In case you need to call corresponding value handler with ONLY corresponding value, you shoud check value name and value handler module which passed as function parameter of handle(), like as follow.

def handle(data_source_name, data_name, value):
    if data_name is "co2":
        # do something
        # do nothing

Or, use config file mention later, which can relate value and value handler one to one.

Set Sensor and Value handlers by TOML formatted config file.

You can specify one to one relation with which sensor handler's which value and corresponding value handler, by config file. The contents are expected as follows:

  handler   = "dht22"
    name = "temp"
    handlers = [
    name = "humidity"
    handlers = [
    name = "humiditydeficit"
    handlers = [

  handler   = "mh-z19"
    name = "co2"
    handlers = [

The config file of pondslider consist of an array of table [[sensors]]. The pondslider read this array, then read each sensor handler and call corresponding value handler.

The element of sensors have a couple of keys, the one is handler which indicate corresponding Sensor handler, the other is [[sensors.values]] which indicate corresponding Value handlers.

[[sensors.values]] have also a couple of kyes, the one is name which indicate correcponding red sensor value name, which is the key of the dictionally of Sensor handlers read() function's return. The others are handlers array which indicate value handler module. The handle() funcitons of these handler are called Only with the red sensor value which has same name, unlike the valuehandlers specified by command-line option value_handlers is called with All value red from All Sensor handlers.

The config file is specified by command-line option --config. With out --config option, the pondslider search the file named config.toml on the current working directory and use it if found.

Add python module search path

In case your handler module is not linked by standard python module search path, you can tell the pondslider to add search path by command-line option --imppaths as follows:

  --imppaths IMPPATHS [IMPPATHS ...]
                        list of full path for python modules import path like
                        as "/home/pi/mh-z19 /tmp/handler" .

For example, in case your mh-z19 sensor handler is in /home/pi/mh-z19 and your send handler is in /home/pi/handlers/, you can read mh-z19 and send the value as follows:

sudo python -m pondslider --sensor_handlers mh_z19 --value_handlers sender.monitor.send --imppaths /home/pi/mh-z19 /home/pi/handlers

Note, mh-z19 need to read serial interface and it might be necessary of sudo.

How to use

as python program.

usage: python -m pondslider [-h] [--config CONFIG] [--imppaths IMPPATHS [IMPPATHS ...]]
                  [--interval INTERVAL]
                  [--sensor_handlers SENSOR_HANDLERS [SENSOR_HANDLERS ...]]
                  [--value_handlers VALUE_HANDLERS [VALUE_HANDLERS ...]]

optional arguments:
  -h, --help            show this help message and exit
  --config CONFIG       config file for handler specification.
  --imppaths IMPPATHS [IMPPATHS ...]
                        list of full path for python modules import path like
                        as "/home/pi/mh-z19 /tmp/handler" .
  --interval INTERVAL   minute of interval to repeat. no repeat in case not
                        set." .
  --sensor_handlers SENSOR_HANDLERS [SENSOR_HANDLERS ...]
                        list of sensor handler modules as "
                        dht22" .
  --value_handlers VALUE_HANDLERS [VALUE_HANDLERS ...]
                        list of value handler modules as "sender.monitor.send
              " .

The path specified by --imppaths is used ad additional Python import library path. With --interval option, pondslider repeat it in specified interval minutes. Without --interval, just run one time and quit.

as python library.

import pondslider

print (


Any questions, suggestions, reports are welcome! Please make issue without hesitation!


  • 0.1.1 2018.11.03 first version self-forked from sensorhandler.
  • 0.2.1 2018.11.06 add --interval option.
  • 0.2.2 2018.11.06 minor fix: remove redundant print
  • 0.3.1 2018.11.07 add --sensor_handlers and --value_handlers
  • 0.3.7 2018.11.19 fix missing requires
  • 0.4.8 2022.03.23 Bullseye support: fix issue #1 occured with Bullseye.
  • 0.5.1 2022.03.26 add --version

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