Python 3 – File flush() Method
When working with files in Python, we often need to ensure that the data we have written to the file has actually been saved to disk. This is where the flush()
method comes in handy.
The flush()
method is used to force any buffered data to be written to the file. By default, when you write to a file, Python buffers the data in memory before writing it to the file. This can be useful for performance reasons, as writing to disk can be slow. However, if you need the data to be written immediately, you can call the flush()
method to force Python to write it to disk.
Here’s an example of how to use the flush()
method in Python:
file = open("example.txt", "w")
file.write("Hello, World!")
file.flush()
In this example, we open a file called “example.txt” in write mode. We then write the string “Hello, World!” to the file and call the flush()
method to ensure that the data is written to disk.
It’s worth noting that calling flush()
doesn’t guarantee that the data has actually been written to disk. There may still be delays due to disk caching or other factors. However, calling flush()
does ensure that the data is written to the buffer, which reduces the risk of data loss in the event of a crash or power failure.
Automatic Buffering
In Python, files are automatically buffered when opened in text mode (i.e., without the “b” mode flag). This means that data is buffered in memory before being written to the file.
By default, Python uses a block buffering scheme, which means that data is written to the buffer in chunks (or blocks) of a specific size. The size of the buffer varies depending on the operating system, but is usually around 8192 bytes.
Here’s an example of how to write to a file with automatic buffering in Python:
file = open("example.txt", "w")
for i in range(10):
file.write("Line {}\n".format(i))
file.close()
In this example, we open a file called “example.txt” in write mode. We then write 10 lines of text to the file using a loop. Because the file is opened in text mode, Python automatically buffers the data in memory before writing it to disk.
Disabling Buffering
Sometimes, you may want to disable buffering altogether and write data directly to disk as soon as it’s written to the file object. You can do this by opening the file in binary mode (“wb”) and setting the buffer size to 0. This tells Python to write data directly to disk as soon as it’s written to the file object.
Here’s an example of how to disable buffering in Python:
file = open("example.txt", "wb", buffering=0)
file.write(b"Hello, World!\n")
In this example, we open a file called “example.txt” in write mode and binary mode, and set the buffer size to 0. We then write the string “Hello, World!\n” to the file, which is immediately written to disk.
Conclusion
The flush()
method is a useful way to ensure that data is written to a file immediately, reducing the risk of data loss in the event of a crash or power failure. By default, Python automatically buffers data when writing to a file in text mode, but you can disable buffering and write data directly to disk by opening the file in binary mode with a buffer size of 0.