Make ipython notebook print in real time

问题:

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.

回答1:

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)  

回答2:

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

回答3:

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