How to run a Python Script from Deno?

Question

I have a python script with the following code:

print("Hello Deno")

I want to run this python script (test.py) from test.ts using Deno. This is the code in test.ts so far:

const cmd = Deno.run({cmd: ["python3", "test.py"]});

How can I get the output, of the python script in Deno?

Answer 1

To execute a python script from Deno you need to use Deno.Command

const command = new Deno.Command('python3', {
  args: [ "test.py" ],
});
const { code, stdout, stderr } = await command.output();
console.log(new TextDecoder().decode(stdout));
console.log(new TextDecoder().decode(stderr));

---

Old answer: Deno.run is now deprecated in favor of Deno.Command

Deno.run returns an instance of Deno.Process. In order to get the output use .output(). Don't forget to pass stdout/stderr options if you want to read the contents.

// --allow-run
const cmd = Deno.run({
  cmd: ["python3", "test.py"], 
  stdout: "piped",
  stderr: "piped"
});

const output = await cmd.output() // "piped" must be set
const outStr = new TextDecoder().decode(output);

const error = await cmd.stderrOutput();
const errorStr = new TextDecoder().decode(error);

cmd.close(); // Don't forget to close it

console.log(outStr, errorStr);

---

If you don't pass stdout property you'll get the output directly to stdout

 const p = Deno.run({
      cmd: ["python3", "test.py"]
 });

 await p.status();
 // output to stdout "Hello Deno"
 // calling p.output() will result in an Error
 p.close()

---

You can also send the output to a File

// --allow-run --allow-read --allow-write
const filepath = "/tmp/output";
const file = await Deno.open(filepath, {
      create: true,
      write: true
 });

const p = Deno.run({
      cmd: ["python3", "test.py"],
      stdout: file.rid,
      stderr: file.rid // you can use different file for stderr
});

await p.status();
p.close();
file.close();

const fileContents = await Deno.readFile(filepath);
const text = new TextDecoder().decode(fileContents);

console.log(text)

---

In order to check status code of the process you need to use .status()

const status = await cmd.status()
// { success: true, code: 0, signal: undefined }
// { success: false, code: number, signal: number }

---

In case you need to write data to stdin you can do it like this:

const p = Deno.run({
    cmd: ["python", "-c", "import sys; assert 'foo' == sys.stdin.read();"],
    stdin: "piped",
  });


// send other value for different status code
const msg = new TextEncoder().encode("foo"); 
const n = await p.stdin.write(msg);

p.stdin.close()

const status = await p.status();

p.close()
console.log(status)

---

You'll need to run Deno with: --allow-run flag in order to use Deno.run