How Does Data Flushing Work in Python File Operations?

Data Flushing in Python File Operations

When working with files in Python, data is not immediately written to disk but is instead held in a buffer until a specific condition is met, known as flushing. This behavior occurs both when writing to files and stdout.

File Flushing

By default, Python utilizes the operating system's default buffer settings when working with file operations. This means that data is flushed to disk according to the operating system's standard buffering policy. However, you can use the buffering parameter in the open function to customize the buffering behavior:

• 0: Unbuffered, writes directly to disk
• 1: Line buffered, writes after each newline
• Any positive value: Buffer size in bytes
• Negative value: Use system default (usually line buffered for tty devices and fully buffered for files)

stdout Flushing

As for flushing to stdout, Python typically flushes to the terminal after each newline character. However, when stdout is redirected to a file, the buffering behavior may vary:

• If the file is a tty (terminal) device, Python behaves similarly to flushing to stdout.
• If the file is a non-tty device, Python may utilize the buffer settings specified through the buffering parameter or the operating system's defaults.

Code Example

To set unbuffered flushing for file operations, use the following code:

bufsize = 0
f = open('file.txt', 'w', buffering=bufsize)

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