Using the print statement in Python can be very expensive!
Perhaps this is kind of obvious, but I only realized this today. When I'm hacking on a piece of code containing a large for-loop in some algorithm, I'm often printing the current iteration to the console to keep a tab on the progress.
Consider this trivial example:
j = 0
for i in xrange(4096**2):
j += i
print i
This outputs a fast scrolling list of integers so I can keep track of progress, but this results in the following running time on the console:
$ time python print_time.py
...
...
16777215
real 11m5.059s
user 1m16.077s
sys 1m8.568s
Running the same code without the print statement takes a lot less time:
$ time python print_time.py
real 0m13.585s
user 0m13.569s
sys 0m0.008s
It's not because of the performance of the print statement,
but the ability of the console to process all that output.
