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Ipython Notebook doesn't seem to print results in real time, but seems to buffer in a certain way and then bulk output the prints. How can I make ipython print my results as soon as the print command is processed?

Example code:

import time


def printer():
    for i in range(100):
        time.sleep(5)
        print i

Supposing that the above code is in a file that is imported. How could I make it that when I call the printer function it prints a number every 5 seconds and not all the numbers at the very end?

Please note that I cannot edit the function printer() because I get it from some external module. I want the to change the configs of ipython notebook somehow so that it doesn't use a buffer. Therefore, I also do not wish to use sys.stdout.flush(), I want to do it in real-time according to the question, I don't want any buffer to start with.

I also tried loading ipython notebook with the command:

ipython notebook --cache-size=0

but that also doesn't seem to work.

Peter O.
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patapouf_ai
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  • Thanks. My question is slighly different. I don't want to change the function printer() because I get it though importing a module which I don't want to change. I simply want to change the behaviour of ipython. So the solutions proposed in the above question don't work for me because I can't add sys.stdout.flush() to the function. What I want is that there be no buffer in ipython notebook. That it outputs everything automatically. – patapouf_ai Apr 21 '15 at 13:48
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    You could monkeypatch the printer function. – syntonym Apr 21 '15 at 13:51
  • Possibly, but there should be a way to unbuffer ipython notebook stdout no? – patapouf_ai Apr 21 '15 at 14:01
  • With the added requirement you can find [some answers here](http://stackoverflow.com/questions/230751/how-to-flush-output-of-python-print?rq=1) – Carsten Apr 21 '15 at 16:22
  • Thanks, but I couldn't really find anything that works. – patapouf_ai Apr 22 '15 at 07:59
  • Title should be "Make ipython Notebook print in psuedo real time." There is no such thing as Real Time in Python. lol – Matt Jul 03 '15 at 00:39

4 Answers4

16

This is merely one of the answers to the question suggested by Carsten incorporating the __getattr__ delegation suggested by diedthreetimes in a comment:

import sys
oldsysstdout = sys.stdout
class flushfile():
    def __init__(self, f):
        self.f = f
    def __getattr__(self,name): 
        return object.__getattribute__(self.f, name)
    def write(self, x):
        self.f.write(x)
        self.f.flush()
    def flush(self):
        self.f.flush()
sys.stdout = flushfile(sys.stdout)

In the original answer, the __getattr__ method is not implemented. Without that, it fails. Other variants in answers to that question also fail in a notebook.

In a notebook, sys.stdout is an instance of IPython.kernel.zmq.iostream.OutStream and has a number of methods and attributes not present in the usual sys.stdout. Delegating __getattr__ allows a flushfile to masquerade as a ...zmq.iostream.OutStream duck.

This works in a python 2.7 notebook run with ipython 3.1.0

Community
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drevicko
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12

Since Python 3.3, print() has an additional flush argument that can be used to force flushing:

for i in range(10):
    print(i, flush=True)
    time.sleep(1)
kmandov
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2

Try this:

from IPython.display import display, clear_output

display("Hello World") # print string
display(df) # print object such as dataframe

clear_output(wait=True) # use this if need to clear the output before display, good for dynamic updates
topace
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0

Additionally, you can use the carriage return character:

from time import sleep
for i in range(10):
    print(i, end='\r')
    sleep(1)

Or if you're using Jupyter Notebooks:

from IPython.display import clear_output
from time import sleep
for i in range(10):
    print(i)
    sleep(1)
    clear_output(wait=True)
ahmelq
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