For example, suppose you have a generator and you want to obtain slices from it.Ĭonsider the following fibonacci generator from which we obtain a few values using islice(). Fibonacci GeneratorĪnother difference is that islice() accepts an iterable while the slice syntax requires an array. What is the difference between the array slice syntax and islice()? Well, the slice syntax allows you to select a single slice, whereas islice() allows you to loop over multiple slices in an ordered fashion. Difference between Array Slice Syntax and islice() Print list(itertools.islice(a, 4, None, 2))ģ.1. In the following example, islice() is used to select elements starting with fourth, skipping alternate items. print list(itertools.islice(string.ascii_lowercase, 0, None, 3)) The following example extracts every third character from the alphabet. The next function in the collection is itertools.islice() which returns an iterator for looping over slices in some ordered fashion. While this might not matter for small lists, it makes a difference when processing a large number of items. Well, itertools.ifilter() returns an iterator while filter() returns a list. So what is the difference between ifilter() and filter()? Python has a global function called filter() which also filters items in a list through a predicate function. Difference between ifilter() and filter() print 'randoms div 3: ', list(itertools.ifilter(lambda n : not n % 3, ))Ģ.1. Or some random numbers divisible by 3? You get the picture. Select a few random even integers? print 'random evens: ', list(itertools.ifilter(lambda n : n % 2 = 0, )) print list(itertools.ifilter(lambda c : c > 'e', 'abcdefg')) In this article, we present a few examples of ifilter(), islice(), imap() and izip().įirst off, we have itertools.ifilter() which filters an iterable or a list for items for which a predicate function returns true.Ĭonsider this simple example which selects all characters with a numeric value greater than ‘e’. We have covered count(), cycle() and chain() in the first part of this series, and compress(), dropwhile(), and groupby() in the second part. Python provides the itertools package which provides convenience functions for many common iterator operations. ![]() Iteration continues until the longest iterable is exhausted. ![]() If the iterables are of uneven length, missing values are filled-in with fillvalue. Make an iterator that aggregates elements from each of the iterables. Used for lock-step iteration over several iterables at a time. Like zip() except that it returns an iterator instead of a list. if you have a really big list you want to be handled than you can take a look at izip: ![]() Now how zip() function can be rewritten to understand what is it for:Īnd in case when you limited my memory and performance e.g. The returned list is truncated in length to the length of the shortest argument sequence. This function returns a list of tuples, where the i-th tuple contains the i-th element from each of the argument sequences or iterables. In this post i will try to explain for what purpose it can be used and how. ![]() Think that all of you seen a code where built-in zip function used.
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