I'm learning Python and want to make a terminal version of the T-Rex runner game. Programs such as Fedora's package manager show download progress by updating a status bar in place instead of printing a new line for every frame. For example, the progress indicator moves across the same line while the elapsed time changes.
How does the terminal do this? I understand that output can be written with echo or print, but normally each update appears on a new line. What technique should I use in Python to refresh the display smoothly?
2 Answers
For a simple progress bar, you usually don't need a full terminal interface. Print the new text with a carriage return and make sure the output is flushed immediately:
`import sys, time`
`for i in range(101):`
` sys.stdout.write(f"rProgress: {i}%")`
` sys.stdout.flush()`
` time.sleep(0.05)`
If a later message is shorter than the previous one, clear or pad the line so leftover characters don't remain visible.
The basic trick is a carriage return, written as `r`. It moves the cursor back to the beginning of the current line without creating a new line, so the next output overwrites the previous frame. In Python, you can do something like `print(f"Progress: {percent}%", end="r", flush=True)`.
For more advanced cursor movement, clearing, colors, and multi-line interfaces, terminals provide control sequences. Tools such as `terminfo` and `tput` know which sequences are appropriate for the current terminal, and Python includes the `curses` module for building more complex terminal applications.
A carriage return (CR) is `r`, which returns the cursor to the start of the line. A line feed (LF) is `n`, which moves down to the next line. Using `r` without `n` is what lets you replace the current line instead of adding another one.