47 — Progress — a bar in the terminal

Long tasks deserve feedback. A progress bar is a row of # that grows while a loop runs. Instead of printing new lines, it redraws the same line — so the terminal shows one row filling up. This guide builds one with print and \r (a carriage return).

#Steps

1. print() normally ends with a newline, so a second print drops to a new row. end="\r" replaces the newline with a carriage return, which sends the cursor back to the start of the same row — the next print overwrites it:

   print("Hello", end="\r")
   print("World")
   

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   Only World is visible at the end; the second call overwrote the first row.

2. Repeat the overwrite with a for loop and a growing row of #. "#" * i is a string of i hashes — "#" * 3 is "###":

   for i in range(1, 11):
       print("#" * i, end="\r")
   print()
   

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   Each pass redraws the row one hash longer, so the bar fills left to right. The bare print() after the loop ends with a newline, so later output starts on a fresh row.

3. The bar moves too fast to watch. import time loads the clock, and time.sleep(0.2) pauses for two tenths of a second each pass:

   import time
   
   for i in range(1, 11):
       print("#" * i, end="\r")
       time.sleep(0.2)
   print()
   

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4. The whole program. Save progress.nme:

   # progress.nme — a terminal progress bar that fills a row.
   # Run: nme r progress
   #
   # A row of # grows from 1 to 10. The \r returns to the start
   # of the row, so each longer row overwrites the one before it,
   # and time.sleep pauses so you can watch the bar fill.
   # The bar runs 10 steps, then a final print() moves to a new row.
   
   import time
   
   steps = 10
   show "Working..."
   # Each pass builds one row and redraws it in place.
   for i in range(1, steps + 1):
       filled = "#" * i
       percent = i * 10
       print(f"{filled} {percent}%", end="\r")
       time.sleep(0.2)
   print()
   show "Done!"
   

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   The bar grew a percent column: percent = i * 10 turns step 1 into 10% and step 10 into 100%.

5. Run it:

   nme r progress
   

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   Working...
   ########## 100%
   Done!
   

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   On a real terminal the ten rows # 10% through ########## 100% replace each other on the same line, so you see the bar fill one hash at a time. In printed output only the final full bar survives.

#Try it yourself

Change the loop to count down: range(10, 0, -1) draws a full bar that empties to one hash. Or replace "#" with "=" and watch a different character fill the row.

#What you learned

• print(..., end="\r") replaces the newline with a carriage return.
• "#" * i repeats a string — the loop draws a growing bar on one row.
• import time and time.sleep(0.2) pause between steps.
• A progress bar is just a loop that redraws one row until it is full.