Python write to file flush

Description

Python file method flush() flushes the internal buffer, like stdio's fflush. This may be a no-op on some file-like objects.

Python automatically flushes the files when closing them. But you may want to flush the data before closing any file.

Syntax

Following is the syntax for flush() method −

fileObject.flush(); 

Parameters

• NA

Return Value

This method does not return any value.

Example

The following example shows the usage of flush() method.

#!/usr/bin/python

# Open a file
fo = open("foo.txt", "wb")
print "Name of the file: ", fo.name

# Here it does nothing, but you can call it with read operation.
fo.flush()

# Close opend file
fo.close()

When we run above program, it produces following result −

Name of the file:  foo.txt

python_files_io.htm

1. How often does Python flush to a file?
2. How often does Python flush to stdout?

I'm unsure about (1).

As for (2), I believe Python flushes to stdout after every new line. But, if you overload stdout to be to a file, does it flush as often?

asked Jul 2, 2010 at 16:30

Tim McJiltonTim McJilton

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0

For file operations, Python uses the operating system's default buffering unless you configure it do otherwise. You can specify a buffer size, unbuffered, or line buffered.

For example, the open function takes a buffer size argument.

http://docs.python.org/library/functions.html#open

"The optional buffering argument specifies the file’s desired buffer size:"

• 0 means unbuffered,
• 1 means line buffered,
• any other positive value means use a buffer of (approximately) that size.
• A negative buffering means to use the system default, which is usually line buffered for tty devices and fully buffered for other files.
• If omitted, the system default is used.

code:

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

zyxue

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answered Jul 2, 2010 at 19:02

Corey GoldbergCorey Goldberg

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7

You can also force flush the buffer to a file programmatically with the flush() method.

with open('out.log', 'w+') as f:
    f.write('output is ')
    # some work
    s = 'OK.'
    f.write(s)
    f.write('\n')
    f.flush()
    # some other work
    f.write('done\n')
    f.flush()

I have found this useful when tailing an output file with tail -f.

Martin Thoma

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answered Mar 10, 2011 at 5:13

6

I don't know if this applies to python as well, but I think it depends on the operating system that you are running.

On Linux for example, output to terminal flushes the buffer on a newline, whereas for output to files it only flushes when the buffer is full (by default). This is because it is more efficient to flush the buffer fewer times, and the user is less likely to notice if the output is not flushed on a newline in a file.

You might be able to auto-flush the output if that is what you need.

EDIT: I think you would auto-flush in python this way (based from here)

#0 means there is no buffer, so all output
#will be auto-flushed
fsock = open('out.log', 'w', 0)
sys.stdout = fsock
#do whatever
fsock.close()

answered Jul 2, 2010 at 16:37

KLee1KLee1

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You can also check the default buffer size by calling the read only DEFAULT_BUFFER_SIZE attribute from io module.

import io
print (io.DEFAULT_BUFFER_SIZE)

answered May 20, 2016 at 15:28

N RandhawaN Randhawa

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1

Here is another approach, up to the OP to choose which one he prefers.

When including the code below in the __init__.py file before any other code, messages printed with print and any errors will no longer be logged to Ableton's Log.txt but to separate files on your disk:

import sys

path = "/Users/#username#"

errorLog = open(path + "/stderr.txt", "w", 1)
errorLog.write("---Starting Error Log---\n")
sys.stderr = errorLog
stdoutLog = open(path + "/stdout.txt", "w", 1)
stdoutLog.write("---Starting Standard Out Log---\n")
sys.stdout = stdoutLog

(for Mac, change #username# to the name of your user folder. On Windows the path to your user folder will have a different format)

When you open the files in a text editor that refreshes its content when the file on disk is changed (example for Mac: TextEdit does not but TextWrangler does), you will see the logs being updated in real-time.

Credits: this code was copied mostly from the liveAPI control surface scripts by Nathan Ramella

answered Jul 29, 2016 at 9:09

MattijsMattijs

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How do you flush a file in Python?

What does it mean to flush a file?

Which method is used to clear the buffer and write contents in buffer to the file this is how programmers can forcefully write to the files as when required?

What does flush true do in Python?