How do Python scripts clear output to cursor position at a specific location?

How to accurately clear output from a specific area in Python scripts?

In Python scripts, especially when dynamically updating the interface or displaying progress bars, clearing the previous output and keeping the cursor position is a common requirement. This article will explore how to achieve this goal effectively, especially when dealing with multiple progress bars or output areas.

I tried to clear the output using the \r carriage return character, but it was limited to clearing the current line and could not clear the previous output area. We need to use ANSI escape code to achieve more accurate control.

Problem analysis:

Simple \r can only move the cursor back to the beginning of the line, and will not clear the previous output content.

Solution:

1. \r Return: Clear the current line

   \r is still useful for updating output on the same line, such as the percentage of update progress bars:

    import time
   
   for i in range(10):
       print(f"Progress: {i*10}%", end="\r", flush=True)
       time.sleep(1)

2. ANSI escape code: Clear the specified area

   ANSI escape code allows for finer control of terminal output. The following function clears the output of the specified number of rows:

    import sys
   
   def clear_lines(num_lines):
       for _ in range(num_lines):
           sys.stdout.write("\033[F\033[K") # Move the cursor up and clear the line

   \033[F Move the cursor up one line, \033[K Clear the content from the cursor to the end of the line.

3. Use in combination: More flexible control

   Combining \r and ANSI escape codes, more flexible control can be achieved: first use ANSI escape code to clear the previous output area, and then use \r to update the new output at the same location.

Code application example:

Assuming that the previous output occupies 5 lines, these lines need to be cleared before displaying the second progress bar:

 if crawler_name == 'Timed Task':
    clear_lines(5) # Clear the previous 5 lines of output Crontab().control_panel() # Show new progress bar or output

Summarize:

By combining \r and ANSI escape code, the terminal output of Python scripts can be effectively controlled, and the output content in specific areas can be accurately cleared, thereby improving the user experience and interface aesthetics. It should be noted that the compatibility of ANSI escape code depends on the terminal type, and some terminals may not support these escape codes.

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