stdout redirection issues

[henryiii]

There are several issues with the example of the DummyTqdmFile in the readme:

1. file = None in the class makes it a class level variable, rather than object level. It should be removed or changed to __slots__ = ("file",).
2. The catch exception line is useless, all it does is rethrow. You can leave it out safely. (finally does the job)
3. Mentioning redirect_stdout (Python 3.4+) and redirect_stderr (Python 3.5+) in contextlib might be nice for people using those versions of Python.
4. tdqm.write does not behave like a normal .write, it adds a \n. This causes lots of issues with this overwrite, especially inside nested progress bars. I worked on this a while, and could not get the redirect to work and produce the correct override.
5. This would be a great utility to have in the library. You could add a parameter for the progress bar so that it could be general to notebook progress bars too (if needed)

EDIT: I forget to add file=sys.stdout, dynamic_ncols=True, that solved 4.

Here's an example of the updated example with fixes for several of the points above:

from contextlib import contextmanager, redirect_stdout, redirect_stderr
import sys

class DummyTqdmFile(object):
    """Dummy file-like that will write to tqdm"""
    __slots__ = ("file", "progress")
    
    def __init__(self, file, progress):
        self.file = file
        self.progress = progress

    def write(self, x):
        # Avoid print() second call (useless \n)
        if len(x.rstrip()) > 0:
            self.progress.write(x.strip(), file=self.file)

    def flush(self):
        return getattr(self.file, "flush", lambda: None)()

# All Python versions:
def tqdm_redirect(progress):
    orig_out_err = sys.stdout, sys.stderr
    try:
        sys.stdout = DummyTqdmFile(sys.stdout, progress)
        sys.stderr = DummyTqdmFile(sys.stderr, progress)
        yield orig_out_err[0]
    # Always restore sys.stdout/err if necessary
    finally:
        sys.stdout, sys.stderr = orig_out_err

# Python 3.5+ version:
@contextmanager
def tqdm_redirect(progress):
    orig_out = sys.stdout
    with redirect_stdout(DummyTqdmFile(sys.stdout, progress)), redirect_stderr(DummyTqdmFile(sys.stderr, progress)):
        yield orig_out

Note that the final progress bar covers up the prompt if leave is not set to False.

[casperdcl]

technically shouldn't strip() either since write() commands in general don't

[casperdcl]

is (5) solved by from tqdm.auto import tqdm?