Asynchrous issue when using clear_display and print x,y,z

[piti118]

A minor issue

from IPython.core.display import clear_output
import time
class xxx:
    def __init__(self,color):
        self.color = color
    def _repr_html_(self):
        return '<span style="color:%s">woot</span>'%self.color
for i in range(10):
    x = xxx(['red','green','blue'][(i%3)])
    print 1,2,3
    clear_output(stdout=False, stderr=False, other=True)
    display(x)
    time.sleep(2)

This produce a funny looking output like

1 2 3
1
 2 3
1
.
.
.

Which the raw html is

<pre> 1 2 3
1</pre>

then

<pre>2 3
1
</pre>

While

print 1,
print 2,
print 3,

works just fine. It also works fine if I remove sleep function.

[minrk]

The issue is (as usual with print weirdnesses) an issue of display_pub and print talking on the same channel, but print statements not writing to the stream until stdout.flush() is called, which is triggered implicitly and asynchronously by some arcane magic.

Solution: display_pub methods should imply sys.stdout/err.flush() to preserve ordering.

See PR #1541 for such a fix.