Difference between two snippets of code?

Question

Is there any difference in terms of performance in doing this:

for i in range(T):  
      arr = [int(arr_temp) for arr_temp in input().strip().split(' ')]

and this:

for i in range(T):
    arr = input().strip().split(' ')
    arr = list(map(int, arr))

if yes, which is better?

This is the perfect question to try out yourself; import timeit; timeit.timeit(function). — Adam Barnes
– Adam Barnes, Commented Jul 4, 2016 at 14:53
Which bit are you interested in? Whether inlining the input makes a difference, or whether list(map(...)) performs differently to a list comprehension? — jonrsharpe
– jonrsharpe, Commented Jul 4, 2016 at 14:54
the first loop is there because i need to create T number of arrays. I need to know if using map() and converting each string array into int will increase performance as opposed to using nested loops to achieve the same. — snow
– snow, Commented Jul 4, 2016 at 14:55

tobias_k · Accepted Answer · 2016-07-04 15:09:38Z

2

According to IPython's %timeit function, map is a bit faster:

In [16]: s = ' '.join(map(str, range(1000)))

In [17]: %timeit [int(c) for c in s.split()]
10000 loops, best of 3: 171 µs per loop

In [18]: %timeit list(map(int, s.split()))
10000 loops, best of 3: 138 µs per loop

Tested with IPython 1.2.1 and Python 3.4.3 and with different input sizes (range(1000), range(10), and range(100000)).

Of course, the interesting question is: Is this part of the code slowing down your program (assuming that that's why you are asking, and not out of pure curiosity). Compared to, e.g., reading the input (from a file, I presume?), or doing calculations with the data, it might be pretty insignificant.

edited Jul 4, 2016 at 15:09

answered Jul 4, 2016 at 14:57

tobias_k

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4 Comments

joel goldstick Over a year ago

And both are completely overwhelmed by the I/O input() from the user

dfrib Over a year ago

Is this true for different input sizes? (I.e., no "crossing" in the growth functions for the two alternatives).

tobias_k Over a year ago

@joelgoldstick Depends, maybe the input is coming from a file piped into the script. But I agree that it probably does not matter too much.

tobias_k Over a year ago

@dfri Good point, checking... yes, seems to be pretty much linear in both cases.

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