CODEWITHSUNDEEP
python
Tom
Tom

Reputation: 49

call function inside argument of a function in python

I am starting with python, and I am trying to understand the sample code that Phidget website give to me (I bought a Phidget Bridge 4 input where I have plug on 4 gauge cell). For my project I need to use python but not much use to it.

To read only one channel, sol only one gauge cell with my Phidget bridge, the website give me this code. 

from Phidget22.Phidget import *
from Phidget22.Devices.VoltageRatioInput import *
import time

def onVoltageRatioChange(self, voltageRatio):
    print("VoltageRatio: " + str(voltageRatio))

def main():
    voltageRatioInput0 = VoltageRatioInput()

    voltageRatioInput0.setOnVoltageRatioChangeHandler(onVoltageRatioChange)

    voltageRatioInput0.openWaitForAttachment(5000)

    time.sleep(5)

    voltageRatioInput0.close()

main()

There is the function def onVoltageRatioChange(self, voltageRatio): which takes 2 arguments, self and voltageRatio, and this function is used inside setOnVoltageRatioChangeHandler(onVoltageRatioChange) with no argument. What I mean, it's that I do not get why we give as an argument onVoltageChange (which is normally a function) to the function setOnVoltageRatioChangeHandler...

It someone could explain it to me, it could help me to build my own code... at least try.. thank you

Upvotes: 1

Views: 105

Answers (1)

shayelk
shayelk

Reputation: 1646

Phidget22 knows how to detect a voltage ratio change, but it doesn't know what you want to do with it: maybe you want to sound an alarm. maybe you want to send an email with the new ratio. maybe you just want to print it to the screen.

So it uses setOnVoltageRatioChangeHandler to ask you what you would like to do once it detects this voltage change, saying "hey, if you'll give me a function that takes a voltage ratio, I'll call it when I detect a change" then you can do:

setOnVoltageRatioChangeHandler(soundTheAlarm)

or

setOnVoltageRatioChangeHandler(sendAnEmail)

or:

setOnVoltageRatioChangeHandler(printToScreen)

The supplied onVoltageRatioChange will just print the new value to the screen.

Generally, passing a function as an argument is a great way to give flexibility in the way events are handled. It's basically saying "I know how to detect a certain situation or get a certain value. You let me know what you want me to do once I do"

Upvotes: 2

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