Redirect print command in python script through tqdm.write()

Redirecting sys.stdout is always tricky, and it becomes a nightmare when two applications are twiddling with it at the same time.

Here the trick is that tqdm by default prints to sys.stderr, not sys.stdout. Normally, tqdm has an anti-mixup strategy for these two special channels, but since you are redirecting sys.stdout, tqdm gets confused because the file handle changes.

Thus, you just need to explicitly specify file=sys.stdout to tqdm and it will work:

from time import sleep

import contextlib
import sys

from tqdm import tqdm

class DummyFile(object):
  file = None
  def __init__(self, file):
    self.file = file

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

@contextlib.contextmanager
def nostdout():
    save_stdout = sys.stdout
    sys.stdout = DummyFile(sys.stdout)
    yield
    sys.stdout = save_stdout

def blabla():
  print("Foo blabla")

# tqdm call to sys.stdout must be done BEFORE stdout redirection
# and you need to specify sys.stdout, not sys.stderr (default)
for _ in tqdm(range(3), file=sys.stdout):
    with nostdout():
        blabla()
        sleep(.5)

print('Done!')

I also added a few more tricks to make the output nicer (eg, no useless \n when using print() without end='').

/EDIT: in fact it seems you can do the stdout redirection after starting tqdm, you just need to specify dynamic_ncols=True in tqdm.