EOF Error when trying to execute python 2.7 code from Golang

Question

I've been trying to use a python utility from code that I'm writing in go. I've been trying to use stdin/stdout to communicate between the processes. However, I'm getting an EOF error using python's raw_input(), even if I connect its stdin to go's stdin.

Here is the code to reproduce the issue:

test.go:

package main

import (
    "os"
    "os/exec"
)

func main() {
    cmd := exec.Command("python", "test.py")

    cmd.Stderr = os.Stderr
    cmd.Stdout = os.Stdout
    cmd.Stdin = os.Stdin

    // Start the process
    if err := cmd.Start(); err != nil {
        panic(err)
    }
}

test.py:

while True:
    input = raw_input()
    print input

The error I get is

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    input = raw_input()
EOFError

I don't understand why this would be an issue. Does anybody have any input?

chrk · Accepted Answer · 2017-11-29 00:54:27Z

2

When cmd.Start() returns, the process running test.go exits and its standard input is closed; so, the process running test.py receives EOF.

Modify test.go, adding something like cmd.Wait(), or even just a time.Sleep(300 * time.Second) after the last block, and you'll see what you probably expected.

For instance:

package main

import (
        "fmt"
        "os"
        "os/exec"
) 

func main() {
        cmd := exec.Command("python", "test.py")

        cmd.Stderr = os.Stderr
        cmd.Stdout = os.Stdout
        cmd.Stdin = os.Stdin

        // Start the process
        if err := cmd.Start(); err != nil {
                panic(err)
        }
        if err := cmd.Wait(); err != nil { 
                fmt.Println("cmd.Wait() in parent process:", err)
        }
}

edited Nov 29, 2017 at 0:54

answered Nov 29, 2017 at 0:49

chrk

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1 Comment

spurrkins Over a year ago

Ah, I see. That does make sense. So, what if I want the python script to run indefinitely? Does it make sense for me to just start a new goroutine, start the python process there, then do cmd.Wait() from that routine? Thanks!

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