Why Doesn't Print Output Appear Immediately in the Terminal Without a Newline?

Why Doesn't Print Output Appear Immediately in the Terminal Without a Newline?

Python's default behavior is to buffer output, meaning it stores text in a temporary space before sending it to the terminal. This is done to improve performance by reducing the number of system calls needed.

The Problem

When no newline (n) is included at the end of a print statement or function call, the text is held in the buffer. Only when a newline is encountered or the buffer becomes full is the text flushed and displayed in the terminal.

Python 2.x and 3.x Differences

In Python 2.x, the print statement does not have a flush argument. To flush the buffer without adding a newline, the following approach can be used:

import sys

for i in range(10):
    print '.',
    sys.stdout.flush()

In Python 3.x, the print function includes a flush keyword argument:

for i in range(10):
    print('.', end=' ', flush=True)

Disabling Line Buffering

For scenarios where immediate printing is desired regardless of newline presence, line buffering can be disabled altogether. This can be achieved using:

• sys.stdout.line_buffering = True for Python 2.x
• print(flush=True) for Python 3.x

By disabling buffering, all print calls will be displayed immediately in the terminal without requiring a newline or explicit flushing.

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