bar() prints current position on Windows

[thmsklngr]

Hi,

I just installed your lib, it's great. Unfortunately I have an issue, which I can't explain.

I used your same code:

with alive_bar(1000) as bar:
     for i in range(1000):
             if i % 300 == 0:
                     print('found!')
             time.sleep(0.01)
             bar()

Result:

on 0: found!
on 1: 1
on 2: 2
on 3: 3
on 4: 4
on 5: 5
on 6: 6
on 7: 7
on 8: 8
on 9: 9
on 10: 10
on 11: 11
on 12: 12
on 13: 13
on 14: 14
on 15: 15
on 16: 16
...

So, even though I do not have any kind of print command, there's output.

Any ideas why?

Regards, Thomas

[rsalmei]

Hello @mosesontheweb, thank you, appreciated!

Unfortunately, I can't imagine how this would be possible. Note the code doesn't even include a print(i) to cause that output. Are you really sure this was the code you ran? Which version are you using? Which Python? I've simulated it now, latest version in a Python 3.8:

Regards, Rogério.

[thmsklngr]

Hi,

I'm running Python 3.6.9. Here's a cast I recorded for you: alive_progress

Regards, Thomas

[rsalmei]

Hey, that's bizarre! I don't have the slightest idea how that could happen, I'd say it's impossible without manually fiddling with the source files...

Could you please try in a new virtualenv? I like pyenv-virtualenv very very much, it just takes:

$ pyenv virtualenv 3.6.9 alive-test
$ pyenv shell alive-test

And this shell has that venv activated. Then you could:

$ pip install alive-progress
$ python

Could you please try that?

[rsalmei]

Well, please reopen if you have more information.

[rsalmei]

Hey @mosesontheweb, how are you?

~Why didn't you tell me this was occurring on Windows? It would be super relevant...~

Anyway, I just installed Python on a Windows machine, and experienced this exact issue! All I can say for now is that it really is the bar() handle, but don't have a clue why. Every time it is called, a new line gets printed.

The relevant code seems to be my flush_buffer, which is called on every bar call. That is because if there's anything on print_buffer, it must be flushed to get the correct count, before incrementing it. There it does have a print() statement. https://github.com/rsalmei/alive-progress/blob/master/alive_progress/core/progress.py#L121-L123

But for anything to enter the print_buffer, it must be in: https://github.com/rsalmei/alive-progress/blob/master/alive_progress/core/progress.py#L163-L167

Would it be the \n? Maybe on Windows it would be \r\n? I'm going to open this again, and do some more debugging.

[rsalmei]

Humm, inside WSL (Windows Subsystem for Linux) it does work. Because it's ipython, not because of WSL.

[rsalmei]

Awesome, I found it!!!! Regardless of how bizarre it may seem, it's the return value of bar() that is being printed on screen! I don't know why this Python is doing that, but just commenting that return makes it all work nicely! 😄

[rsalmei]

Ok, I've been using ipython and bpython for so long in my live that I've forgot about this quirk. It's because of Python, the default REPL, that this happens. It has nothing to do with Windows. Even on macOS I can simulate, it is because Python does not know how to ignore a return value. ipython on the other hand, interprets the statement differently, and captures only its final output:

That way, what I am going to do: I'll remove the return value by default, and create a new method called bar.current() that will return the current position if needed. It will be available in the next major 2.0! See #51

[thmsklngr]

Hi, sorry for the late reply. I thought that I mentioned it somewhere, but it seems that I didn't. My bad. But glad to see that you were finally able to reproduce the issue and add a fix in the next major.

Regards, Thomas