How to flush output of print function?

Question

How do I force Python\'s print function to output to the screen?

_{This is not a duplicate of Disable output buffering - the linked question is attempting unbuffe}

Answer 1

Why not try using an unbuffered file?

f = open('xyz.log', 'a', 0)

OR

sys.stdout = open('out.log', 'a', 0)

Answer 2

Since Python 3.3, you can force the normal print() function to flush without the need to use sys.stdout.flush(); just set the "flush" keyword argument to true. From the documentation:

print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)

Print objects to the stream file, separated by sep and followed by end. sep, end and file, if present, must be given as keyword arguments.

All non-keyword arguments are converted to strings like str() does and written to the stream, separated by sep and followed by end. Both sep and end must be strings; they can also be None, which means to use the default values. If no objects are given, print() will just write end.

The file argument must be an object with a write(string) method; if it is not present or None, sys.stdout will be used. Whether output is buffered is usually determined by file, but if the flush keyword argument is true, the stream is forcibly flushed.

Answer 3

I did it like this in Python 3.4:

'''To write to screen in real-time'''
message = lambda x: print(x, flush=True, end="")
message('I am flushing out now...')

Answer 4

Here is my version, which provides writelines() and fileno(), too:

class FlushFile(object):
    def __init__(self, fd):
        self.fd = fd

    def write(self, x):
        ret = self.fd.write(x)
        self.fd.flush()
        return ret

    def writelines(self, lines):
        ret = self.writelines(lines)
        self.fd.flush()
        return ret

    def flush(self):
        return self.fd.flush

    def close(self):
        return self.fd.close()

    def fileno(self):
        return self.fd.fileno()

Answer 5

With Python 3.x the print() function has been extended:

print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)

So, you can just do:

print("Visiting toilet", flush=True)

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Python Docs Entry

Answer 6

I first struggled to understand how the flush option was working. I wanted to do a 'loading display' and here is the solution I found:

for i in range(100000):
    print('{:s}\r'.format(''), end='', flush=True)
    print('Loading index: {:d}/100000'.format(i+1), end='')

The first line flushes the previous print and the second line prints a new updated message. I don't know if an one-line syntax exists here.