Issue importing other modules

Hello everyone,
I am new to nodejs and I want to develop a Dapp based on the Animal Kingdom (zero-to-dapp).

Every time I want to use functions from ‘child_process’ with code like ( for example, adding to Landing.js ):

   var exec = require('child_process').exec;
   exec('python3 '+ 123, function (error, stdout, stderr) {
            console.error('error: ' + error);
        console.log('receive: ' + stdout);

it always fails and shows infomation like:

TypeError: exec is not a function

It seems that it is not imported right. Did I miss some steps or use the wrong way? Any help would be appreciated.