what is the difference between cmd and idle when u

Question

recently I want to add a simple progress bar to my script, I use tqdm to that, but what puzzle me is that the output is different when I am in the IDLE or in the cmd

for example this

from tqdm import tqdm
import time

def test():
    for i in tqdm( range(100) ):
        time.sleep(0.1)

give the expected output in the cmd

30%|███       | 30/100 [00:03<00:07,  9.14it/s]

but in the IDLE the output is like this

  0%|          | 0/100 [00:00<?, ?it/s]
  1%|1         | 1/100 [00:00<00:10,  9.14it/s]
  2%|2         | 2/100 [00:00<00:11,  8.77it/s]
  3%|3         | 3/100 [00:00<00:11,  8.52it/s]
  4%|4         | 4/100 [00:00<00:11,  8.36it/s]
  5%|5         | 5/100 [00:00<00:11,  8.25it/s]
  6%|6         | 6/100 [00:00<00:11,  8.17it/s]
  7%|7         | 7/100 [00:00<00:11,  8.12it/s]
  8%|8         | 8/100 [00:00<00:11,  8.08it/s]
  9%|9         | 9/100 [00:01<00:11,  8.06it/s]
 10%|#         | 10/100 [00:01<00:11,  8.04it/s]
 11%|#1        | 11/100 [00:01<00:11,  8.03it/s]
 12%|#2        | 12/100 [00:01<00:10,  8.02it/s]
 13%|#3        | 13/100 [00:01<00:10,  8.01it/s]
 14%|#4        | 14/100 [00:01<00:10,  8.01it/s]
 15%|#5        | 15/100 [00:01<00:10,  8.01it/s]
 16%|#6        | 16/100 [00:01<00:10,  8.00it/s]
 17%|#7        | 17/100 [00:02<00:10,  8.00it/s]
 18%|#8        | 18/100 [00:02<00:10,  8.00it/s]
 19%|#9        | 19/100 [00:02<00:10,  8.00it/s]
 20%|##        | 20/100 [00:02<00:09,  8.00it/s]
 21%|##1       | 21/100 [00:02<00:09,  8.00it/s]
 22%|##2       | 22/100 [00:02<00:09,  8.00it/s]
 23%|##3       | 23/100 [00:02<00:09,  8.00it/s]
 24%|##4       | 24/100 [00:02<00:09,  8.00it/s]
 25%|##5       | 25/100 [00:03<00:09,  8.00it/s]
 26%|##6       | 26/100 [00:03<00:09,  8.00it/s]
 27%|##7       | 27/100 [00:03<00:09,  8.09it/s]
 28%|##8       | 28/100 [00:03<00:09,  7.77it/s]
 29%|##9       | 29/100 [00:03<00:09,  7.84it/s]
 30%|###       | 30/100 [00:03<00:08,  7.89it/s]
 31%|###1      | 31/100 [00:03<00:08,  7.92it/s]
 32%|###2      | 32/100 [00:03<00:08,  7.94it/s]
 33%|###3      | 33/100 [00:04<00:08,  7.96it/s]
 34%|###4      | 34/100 [00:04<00:08,  7.97it/s]
 35%|###5      | 35/100 [00:04<00:08,  7.98it/s]
 36%|###6      | 36/100 [00:04<00:08,  7.99it/s]
 37%|###7      | 37/100 [00:04<00:07,  7.99it/s]
 38%|###8      | 38/100 [00:04<00:07,  7.99it/s]
 39%|###9      | 39/100 [00:04<00:07,  8.00it/s]
 40%|####      | 40/100 [00:04<00:07,  8.00it/s]
 41%|####1     | 41/100 [00:05<00:07,  8.00it/s]

I also get the same result if I make my own progress bar like

import sys

def progress_bar_cmd(count,total,suffix="",*,bar_len=60,file=sys.stdout):
    filled_len = round(bar_len*count/total)
    percents   = round(100*count/total,2)
    bar        = "#"*filled_len + "-"*(bar_len - filled_len)
    file.write( "[%s] %s%s ...%s\r"%(bar,percents,"%",suffix))
    file.flush()

for i in range(101):
    time.sleep(1)
    progress_bar_cmd(i,100,"range 100") 

why is that????

and there is a way to fix it???

Answer 1

Limiting ourselves to ascii characters, the program output of your second code is the same in both cases -- a stream of ascii bytes representing ascii chars. The language definition does not and cannot specify what an output device or display program will do with the bytes, in particular with control characters such as '\r'.

The Windows Command Prompt console at least sometimes interprets '\r' as 'return the cursor to the beginning of the current line without erasing anything'. In a Win10 console:

>>> import sys; out=sys.stdout
>>> out.write('abc\rdef')
def7

However, when I run your second code, with the missing time import added, I do not see the overwrite behavior, but see the same continued line output as with IDLE.

C:\Users\Terry>python f:/python/mypy/tem.py
[------------------------------------------------------------] 0.0% ...range 100[#-----------------------------------------------------------] ...

On the third hand, if shorten the write to file.write("[%s]\r"% bar), then I do see one output overwritten over and over.

The tk Text widget used by IDLE only interprets \t and \n, but not other control characters. To some of us, this seems appropriate for a development environment, where erasing characters is less appropriate than in a production environment.