Built in support for Postfix dictionaries

[Alex7Li]

Hi, I do a lot of machine learning and I very commonly want to see statistics that are updated as the progress bar passes, like below:

It's not impossible to make this by hand, but it takes a reasonable amount of code which I generally don't want to write when I just want a progress bar. So, I think it would be a worthwhile feature to add a way to set a postfix (like tqdm https://tqdm.github.io/docs/tqdm/#set_postfix).

I already implemented something that works fairly well here:

import time
from rich.pretty import Pretty, pprint, pretty_repr
from rich.progress import (
    BarColumn,
    Progress,
    TextColumn,
    TimeRemainingColumn,
    TaskProgressColumn,
)
from numbers import Number

def format_num(n):
    """
    Intelligent scientific notation (.3g).
    Parameters
    ----------
    n  : int or float or Numeric
        A Number.
    Returns
    -------
    out  : str
        Formatted number.
    """
    f = '{0:.3g}'.format(n).replace('+0', '+').replace('-0', '-')
    n = str(n)
    return f if len(f) < len(n) else n

class MyProgress(Progress):
    def update(self, *args, postfix={}, **kwargs):
      super().update(*args, **kwargs)
      with self._lock:
        task = self._tasks[kwargs['task_id']]
        if len(postfix):
          for key in postfix.keys():
            if isinstance(postfix[key], Number):
              postfix[key] = format_num(postfix[key])
            elif not isinstance(postfix[key], str):
                postfix[key] = str(postfix[key])
        task.postfix =', '.join(f'[green]{key}[/green]=[blue]{postfix[key]}[/blue]'.strip()
                                 for key in postfix.keys()) # Need to update Task class to have a postfix field

    @classmethod
    def get_default_columns(cls):
        return (
            TextColumn("[progress.description]{task.description}"),
            BarColumn(),
            TaskProgressColumn(),
            TimeRemainingColumn(),
            TextColumn("[progress.postfix]{task.postfix}"), # new text column!
        )
      

def example():
  with MyProgress() as pbar:
    t_out = pbar.add_task('epoch', total=6)
    t_in = pbar.add_task('step', total=200)
    for i in range(6):
      pbar.update(task_id=t_in, completed=0)
      for j in range(200):
        time.sleep(.01)
        pbar.update(task_id=t_in, advance=1, postfix={'loss': 100/(i * 150 + j + 1)})
      pbar.update(task_id=t_out, advance=1, postfix={"best_accuracy": f"{i * 5}%", 'mode': "train" if i% 2 == 0 else "validation"})
    

if __name__ == "__main__":
  pprint({'a':5})
  example()

Other than updating the Task class by adding a str postfix field, this is the complete code

I think this would be a pretty useful feature for quite a few people. I can open a pull request if this sounds like a good feature. Or maybe it would be better to implement it another way, one problem with this design is that posfixes won't work on custom progress bars unless you add a textcolumn like TextColumn("[progress.postfix]{task.postfix}").