Ctrl-C in a pager causes program to quit

[amjith]

I'm using echo_via_pager() in my program to display the output through a pager. But while I'm in the pager if Ctrl-C is pressed then system.exit(1) is called, without giving me an opportunity to handle it.

I'm using this inside a repl and I'd like to have the ability to handle Ctrl-C.

Here's an example to reproduce:

import click

@click.command()
@click.option('--foo', prompt=True)
def cli(foo):
    try:
        click.echo_via_pager('foo=%s' % foo)
    except click.Abort:
        print('Tada!')

If you run this example and press Ctrl-C while in the pager, it will print 'Aborted!' and quit the program, I'd expect to see the message 'Tada!' instead.

[untitaker]

You can still catch SystemExit

On 29 May 2015 16:53:19 CEST, Amjith Ramanujam notifications@github.com wrote:

I'm using echo_via_pager() in my program to display the output
through a pager. But while I'm in the pager if Ctrl-C is pressed then
system.exit(1) is called, without giving me an opportunity to handle
it.

I'm using this inside a repl and I'd
like to have the ability to handle Ctrl-C.

Here's an example to reproduce:

import click

@click.command()
@click.option('--foo', prompt=True)
def cli(foo):
   try:
       click.echo_via_pager('foo=%s' % foo)
   except click.Abort:
       print('Tada!')

If you run this example and press Ctrl-C while in the pager, it will
print 'Aborted!' and quit the program, I'd expect to see the message
'Tada!' instead.

---

Reply to this email directly or view it on GitHub:
#350

[amjith]

I tried catching SystemExit and it still doens't work as I expect.

import click

@click.command()
@click.option('--foo', prompt=True)
def cli(foo):
    try:
        click.echo_via_pager('foo=%s' % foo)
    except SystemExit:
        print('Tada!')

It still prints Aborted! and quits the program.

[untitaker]

In my terminal it seems that ^C kills both pager and program and leaves the terminal in an unusuable state.

[untitaker]

In your case you need to catch KeyboardInterrupt though.

[amjith]

You're right if I catch KeyboardInterrupt it is handled. But it still doesn't solve the problem.

Looks like the ^C is surfaced by click but the pager is never killed. So even if I handle the KeyboardInterrupt the less command continues to print the contents on the screen.

I feel like the ^C in the page need to be handled by click here: https://github.com/mitsuhiko/click/blob/master/click/_termui_impl.py#L306..L311

Wrap that line in try/except KeyboardInterrupt and then call c.terminate() and then reraise that KeyboardInterrupt.

Otherwise there is no way for an app to call the echo_via_pager() and keep working when a user presses ^C in the pager.

[untitaker]

I've pushed a fix to 4.x-maintenance and master that fixes your issue. It swallows ^C, echo_via_pager doesn't raise an exception.

This behavior is then consistent with the other pager methods I've tried. I'm not sure if that's the behavior we want, but anything else is fairly hard to implement given the behavior of less.