Why is my Python output delayed, and how can I make it appear in real-time?

Understanding Delayed Terminal Output in Python

Python by default buffers output to enhance performance by transmitting it all at once rather than individually to other programs like the terminal. In the absence of a newline, print statements are typically buffered aline at a time, resulting in a delay in displaying the intended text.

Addressing the Problem

For Single Print Statements:

• Python 3.x: Utilize the flush parameter in the print function to explicitly flush output, as seen below:

for _ in range(10):
    print('.', end=' ', flush=True)
    time.sleep(.2)  # or other time-consuming work

• Python 2.x: Use the .flush method of the sys.stdout stream to force output transmission:

for _ in range(10):
    print '.',
    sys.stdout.flush()
    time.sleep(.2)  # or other time-consuming work

For Multiple Print Statements:

Instead of flushing each print individually, you can completely disable line buffering. Here are some potential solutions:

• Set the environment variable PYTHONUNBUFFERED to True:

  export PYTHONUNBUFFERED=1

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• Use the fcntl module to manipulate file descriptors:

  import fcntl
  
  stdout_fileno = sys.stdout.fileno()
  fcntl.fcntl(stdout_fileno, fcntl.F_SETFL, os.O_NONBLOCK)

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• Use third-party libraries like tqdm or joblib to provide progress bars with real-time updates.

By implementing these techniques, you can ensure that output is displayed immediately in the terminal, providing a more informative and interactive experience during script execution.

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