[CentralOH] Pytest, FileInput, and captured output

[Eric Floehr]

Len,

This may be a long-shot and it's a bit of a hack, but what about using
stderr for output? stderr doesn't get captured by inplace=True. Though I'm
not an expert with pytest and what it might do. Or could you create a
"prompt_user" function that could take a StringIO object for input and
output and pass that through the test since it has a stream-like interface?

Here is a quick test I tried, you could in process_file create and pass in
StringIO's in a pytest test as well.

-------------------

import fileinput
import sys

def prompt_user(prompt, input_stream=sys.stdin, output_stream=sys.stderr):
    output_stream.write(prompt)
    output_stream.flush()
    return input_stream.readline()

def process_file(filename):
    with fileinput.input(files=(filename,), inplace=True) as f:
        for line in f:
            user_input = prompt_user(f"Edit line '{line.strip()}': ")
            print(user_input if user_input else line, end='')

process_file('test.txt')

-------------------

Cheers,
Eric


On Wed, Jul 3, 2024 at 4:32 PM Len Jaffe <lenjaffe at jaffesystems.com> wrote:

> I have a method  that present a user prompt, and returns the respond, and
> method tests using pytest.
>
> First draft using print(), input() and pytest capsys.out worked fine.
>
> But now I want to move the prompt into another method which is called
> inside a FileInput context manager.  The FileInput is instantiated with
> inplace=True, so I can no longer use stdout for the use prompt since
> fileinput uses it for the in-place processing.
>
> I have no problem opening /dev/tty on new fds to do the prompt and
> response, but I'm stumped trying to figure out an alternative solution for
> capturing that output in pytest.
>
> My web searches found nothing of value. Please help.
>
> Suggestions and advice would be greatly  appreciated.
>
> Len
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