How to Force Immediate Terminal Output in Python?

Persistent Terminal Output with Python

In Python, there is an issue where print outputs may not immediately appear in the terminal if there is no newline present. This occurs due to output buffering, where output is temporarily stored to improve performance.

What Happens?

By default, the terminal divides output into lines. If a line ends without a newline character, the output remains in a buffer until it's complete. As a result, when there's no newline after a print statement, the output is not displayed until the loop or program terminates.

Fixing the Issue

For Single Prints:

In Python 3, the print function accepts a flush argument. Setting it to True forces output to be displayed immediately:

import time

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

In Python 2, where print is a statement, use the flush method of the standard output stream (sys.stdout):

import time

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

For Multiple Prints:

Instead of flushing after each print, you can disable output line buffering altogether for more efficient handling of multiple prints. Multiple solutions are available:

• Use print(file=sys.stderr) to redirect output to standard error, which is not buffered.
• Use sys.stdout.writelines with a list of all print statements to output them in one go.
• Install the unbuffered package and utilize its Unbuffered class to create an unbuffered stdout stream.

The above is the detailed content of How to Force Immediate Terminal Output in Python?. For more information, please follow other related articles on the PHP Chinese website!