Cannot Launch Interactive Program While Piping to Script in Python

Question

I have a python script that needs to call the defined $EDITOR or $VISUAL. When the Python script is called alone, I am able to launch the $EDITOR without a hitch, but the moment I pipe something to the Python script, the $EDITOR is unable to launch. Right now, I am using nano which shows

Received SIGHUP or SIGTERM

every time. It appears to be the same issue described here.

sinister:Programming [1313]$ echo "import os;os.system('nano')" > "sample.py" 
sinister:Programming [1314]$ python sample.py
# nano is successfully launched here.
sinister:Programming [1315]$ echo "It dies here." | python sample.py 
Received SIGHUP or SIGTERM

Buffer written to nano.save.1

EDIT: Clarification; inside the program, I am not piping to the editor. The code is as follows:

editorprocess = subprocess.Popen([editor or "vi", temppath])
editorreturncode = os.waitpid(editorprocess.pid, 0)[1]

Answer 1

When you pipe something to a process, the pipe is connected to that process's standard input. This means your terminal input won't be connected to the editor. Most editors also check whether their standard input is a terminal (isatty), which a pipe isn't; and if it isn't a terminal, they'll refuse to start. In the case of nano, this appears to cause it to exit with the message you included:

% echo | nano
Received SIGHUP or SIGTERM

You'll need to provide the input to your Python script in another way, such as via a file, if you want to be able to pass its standard input to a terminal-based editor.

Now you've clarified your question, that you don't want the Python process's stdin attached to the editor, you can modify your code as follows:

editorprocess = subprocess.Popen([editor or "vi", temppath],
                                 stdin=open('/dev/tty', 'r'))

Answer 2

The specific case of find -type f | vidir - is handled here:

foreach my $item (@ARGV) {
    if ($item eq "-") {
        push @dir, map { chomp; $_ } <STDIN>;
        close STDIN;
        open(STDIN, "/dev/tty") || die "reopen: $!\n";
    }

You can re-create this behavior in Python, as well:

#!/usr/bin/python

import os
import sys

sys.stdin.close()
o = os.open("/dev/tty", os.O_RDONLY)
os.dup2(o, 0)
os.system('vim')

Of course, it closes the standard input file descriptor, so if you intend on reading from it again after starting the editor, you should probably duplicate its file descriptor before closing it.