Generator speed in python 3

I am going through a link about generators that someone posted. In the beginning he compares the two functions below. On his setup he showed a speed increase of 5% with the generator.

I'm running windows XP, python 3.1.1, and cannot seem to duplicate the results. I keep showing the "old way"(logs1) as being slightly faster when tested with the provided logs and up to 1GB of duplicated data.

Can someone help me understand whats happening differently?

Thanks!

def logs1():
    wwwlog = open("big-access-log")
    total = 0
    for line in wwwlog:
        bytestr = line.rsplit(None,1)[1]
        if bytestr != '-':
            total += int(bytestr)
    return total

def logs2():
    wwwlog = open("big-access-log")
    bytecolumn = (line.rsplit(None,1)开发者_如何学Python[1] for line in wwwlog)
    getbytes      = (int(x) for x in bytecolumn if x != '-')
    return sum(getbytes)

*edit, spacing messed up in copy/paste

For what it's worth, the main purpose of the speed comparison in the presentation was to point out that using generators does not introduce a huge performance overhead. Many programmers, when first seeing generators, might start wondering about the hidden costs. For example, is there all sorts of fancy magic going on behind the scenes? Is using this feature going to make my program run twice as slow?

In general that's not the case. The example is meant to show that a generator solution can run at essentially the same speed, if not slightly faster in some cases (although it depends on the situation, version of Python, etc.). If you are observing huge differences in performance between the two versions though, then that would be something worth investigating.

In David Beazley's slides that you linked to, he states that all tests were run with "Python 2.5.1 on OS X 10.4.11," and you say you're running tests with Python 3.1 on Windows XP. So, realize you're doing some apples to oranges comparison. I suspect of the two variables, the Python version matters much more.

Python 3 is a different beast than Python 2. Many things have changed under the hood, (even within the Python 2 branch). This includes performance optimizations as well as performance regressions (see, for example, Beazley's own recent blog post on I/O in Python 3). For this reason, the Python Performance Tips page states explicitly,

You should always test these tips with your application and the version of Python you intend to use and not just blindly accept that one method is faster than another.

I should mention that one area that you can count on generators helping is in reducing memory consumption, rather than CPU consumption. If you have a large amount of data where you calculate or extract something from each individual piece, and you don't need the data after, generators will shine. See generator comprehension for more details.

You don't have an answer after almost a half an hour. I'm posting something that makes sense to me, not necessarily the right answer. I figure that this is better than nothing after almost half an hour:

The first algorithm uses a generator. A generator functions by loading the first page of results from the list (into memory) and continually loads the successive pages (into memory) until there is nothing left to read from input.

The second algorithm uses two generators, each with an if statement for a total of two comparisons per loop as opposed to the first algorithm's one comparison.

Also the second algorithm calls the sum function at the end as opposed to the first algorithm that simply keeps adding relevant integers as it keeps encountering them.

As such, for sufficiently large inputs, the second algorithm has more comparisons and an extra function call than the first. This could possibly explain why it takes longer to finish than the first algorithm.

Hope this helps