I was trying to call a python code from my node file.
Here is my node.js Code:
var util = require("util");
var spawn = require("child_process").spawn;
var process = spawn('python',["workpad.py"]);
util.log('readingin')
process.stdout.on('data',function(data){
util.log(data);
});
and my python part:
import sys
data = "test"
print(data)
sys.stdout.flush()
In the cmd window, only util.log('readingin') is shown. What's the problem of my code?
There is no problem ...
Here is a slight tweak of your working code (I convert the buffer to string so its human readable)
// spawn_python.js
var util = require("util");
var spawn = require("child_process").spawn;
var process = spawn('python',["python_launched_from_nodejs.py"]);
util.log('readingin')
process.stdout.on('data',function(chunk){
var textChunk = chunk.toString('utf8');// buffer to string
util.log(textChunk);
});
and here is your python
# python_launched_from_nodejs.py
import sys
data = "this began life in python"
print(data)
sys.stdout.flush()
finally here is output of a run
node spawn_python.js
11 Dec 00:06:17 - readingin
11 Dec 00:06:17 - this began life in python
node --version
v5.2.0
I was also facing the same issue, I found this:
var myPythonScript = "script.py";
// Provide the path of the python executable, if python is available as
// environment variable then you can use only "python"
var pythonExecutable = "python.exe";
// Function to convert an Uint8Array to a string
var uint8arrayToString = function(data){
return String.fromCharCode.apply(null, data);
};
const spawn = require('child_process').spawn;
const scriptExecution = spawn(pythonExecutable, [myPythonScript]);
// Handle normal output
scriptExecution.stdout.on('data', (data) => {
console.log(uint8arrayToString(data));
});
// Handle error output
scriptExecution.stderr.on('data', (data) => {
// As said before, convert the Uint8Array to a readable string.
console.log(uint8arrayToString(data));
});
scriptExecution.on('exit', (code) => {
console.log("Process quit with code : " + code);
});
You could always try something like this:
var child_process = require('child_process');
child_process.exec('python myPythonScript.py', function (err){
if (err) {
console.log("child processes failed with error code: " + err.code);
}
});
you can check this package on npm- native-python
it provides a very simple and powerful way to run python functions from node might solve your problem and actually uses spawn.
import { runFunction } from '@guydev/native-python'
const example = async () => {
const input = [1,[1,2,3],{'foo':'bar'}]
const { error, data } = await runFunction('/path/to/file.py','hello_world', '/path/to/python', input)
// error will be null if no error occured.
if (error) {
console.log('Error: ', error)
}
else {
console.log('Success: ', data)
// prints data or null if function has no return value
}
}
python module
# module: file.py
def hello_world(a,b,c):
print( type(a), a)
# <class 'int'>, 1
print(type(b),b)
# <class 'list'>, [1,2,3]
print(type(c),c)
# <class 'dict'>, {'foo':'bar'}
A more rigorous implementation could also catch raised exceptions and exit codes, as such
var spawn = require("child_process").spawn;
var process = spawn('python',["my_py_file.py"]);
process.stdout.on('data', (data) => {
console.log(data.toString('utf8'));
});
process.stderr.on('data', (stacktrace) => {
console.error(stacktrace.toString('utf8'));
// possibly parse the stack trace to handle distinct exceptions
});
process.on('exit', (exitCode) => {
console.log(`Process ended with code (${exitCode})`);
});
I would personally rely on exit codes to handle different outcomes from my Python script rather than raising exceptions, as the exceptions will most likely need to be manually parsed.
