In our write-up on Python Iterables, we took a brief introduction to the Python itertools module. This is what will be the point of focus in today’s Python itertools tutorial.<\/p>\n
Here, we will learn how to get infinite iterators & Combinatoric Iterators by Python Itertools.<\/p>\n
Along with this, we will learn how Python Iterators terminate the shortest input sequence.<\/p>\n
So, let’s start exploring Python Itertools Tutorial.<\/p>\n
The Python itertools module has functions for creating iterators for efficient looping. While some iterators are infinite, some terminate on the shortest input sequence. Yet, some are combinatoric.<\/p>\n
Benefits of using itertools in Python:<\/strong><\/p>\n Let\u2019s first discuss Python infinite iterators.<\/p>\n Some functions are capable of generating infinite iterators. In this Python Itertools tutorial, we will study the following functions:<\/p>\n count() may take two values- start and step. It then returns a sequence of values from start, with intervals the size of step.<\/p>\n Output<\/strong><\/p>\n Here\u2019s count() with one argument:<\/p>\n Output<\/strong><\/p>\n It takes a step of 1. If we call it without an argument, it starts with 0:<\/p>\n Output<\/strong><\/p>\n cycle() makes an iterator from elements from an iterable, and saves a copy of each.<\/p>\n Once exhausted, it returns elements from that copy. This repeats indefinitely.<\/p>\n Output<\/strong><\/p>\n cycle() can take any kind of iterable.<\/p>\n This will repeat element elem n-times or endlessly into the iterator.<\/p>\n Output<\/strong><\/p>\n Output<\/strong><\/p>\n Combinatorial pertains to the arrangement of, operation on, and selection of discrete mathematical elements. Let\u2019s now talk about combinatoric iterators.<\/p>\n product() returns the Cartesian product of the input iterables. This is equivalent to a nested for-loop.<\/p>\n Output<\/strong><\/p>\n This is equivalent to iterating over this generator object:<\/p>\n Output<\/strong><\/p>\n Let\u2019s take a couple more examples.<\/p>\n Output<\/strong><\/p>\n Because of the repeat argument, the rightmost element advances with every iteration.<\/p>\n Output<\/strong><\/p>\n permutations() returns r-length permutations of elements in the iterable.<\/p>\n It generates all possible permutations in lexicographic order, and there is no repetition of elements.<\/p>\n Output<\/strong><\/p>\n Here, we didn\u2019t pass a second argument to it, so it printed tuples of length 4, which is the length of the iterable.<\/p>\n Now, let\u2019s pass a value of 3 to this code.<\/p>\n Output<\/strong><\/p>\n This returns subsequences of length r from the elements of the iterable.<\/p>\n Output<\/strong><\/p>\n If you noticed, this only returns the tuples that are lexicographically ascending.<\/p>\n Let\u2019s take another example.<\/p>\n Output<\/strong><\/p>\n This returns r-length subsequences of elements of the iterable, where individual elements may repeat.<\/p>\n Output<\/strong><\/p>\n This makes an iterator with accumulated sums (or accumulated results of a binary function specified).<\/p>\n Output<\/strong><\/p>\n This prints the Fibonacci series.<\/p>\n Let\u2019s take another example.<\/p>\n Output<\/strong><\/p>\n Output<\/strong><\/p>\n chain() makes an iterator from elements of the first iterable, then from the second, and so on.<\/p>\n It moves to the next iterable as one iterable exhausts.<\/p>\n Output<\/strong><\/p>\n This is an alternative constructor to chain(). It takes chained inputs from a single iterable argument and evaluates them lazily.<\/p>\n Output<\/strong><\/p>\n You don\u2019t need to additionally import anything for this.<\/p>\n This makes an iterator that filters elements, from data, for which selector values amount to True.<\/p>\n Output<\/strong><\/p>\n As long as the predicate is True, it drops elements from the iterable. As soon as it is False, it starts returning every element.<\/p>\n Output<\/strong><\/p>\n This makes an iterator that filters those elements out from the iterator, for which the predicate is True.<\/p>\n Output<\/strong><\/p>\n Output<\/strong><\/p>\n This makes an iterator that takes the iterable, and returns consecutive keys and groups. These are sub-iterators grouped by the key.<\/p>\n Output<\/strong><\/p>\n islice(iterable,start,stop [,step])<\/p>\n This makes an iterator that returns selected elements from the iterable.<\/p>\n Output<\/strong><\/p>\n Output<\/strong><\/p>\n Output<\/strong><\/p>\n This makes an iterator that takes arguments from the iterable and computes a function.<\/p>\n Output<\/strong><\/p>\n This makes an iterator that returns elements from the iterator as long as the predicate amounts to True. This is in contrast to dropwhile().<\/p>\n Output<\/strong><\/p>\n This splits an iterator into n independent iterators.<\/p>\n Output<\/strong><\/p>\n This makes an iterator by aggregating elements from each iterable. The fillvalue parameter tells it a value to fill for the remaining places in the shorter iterable.<\/p>\n Output<\/strong><\/p>\n Output<\/strong><\/p>\n So, this was all about the Python Itertools Tutorial. Hope you like our explanation.<\/p>\n 1. What are itertools in Python?<\/p>\n 2. What does itertools do in Python?<\/p>\n 3. Is itertool a standard library in Python?<\/p>\n 4. What are the benefits and limitations of using itertools in Python?<\/p>\n 5. How does itertools work in Python?<\/p>\n Processing big data often means iterating over millions of records. The itertools module supplies memory-friendly \u201clazy\u201d iterators that yield items one by one instead of building giant lists. itertools.count() creates an infinite counter, cycle() repeats a pattern, and repeat(x, n) stamps out a value multiple times\u2014without heavy RAM costs.<\/p>\n Hope you enjoyed the Python itertools tutorial.<\/p>\n","protected":false},"excerpt":{"rendered":" In our write-up on Python Iterables, we took a brief introduction to the Python itertools module. This is what will be the point of focus in today’s Python itertools tutorial. Here, we will learn...<\/p>\n","protected":false},"author":5,"featured_media":36198,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[46],"tags":[2653,6697,7340,10622,10625,10626],"class_list":["post-10483","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-python","tag-combinatoric-iterators","tag-infinite-iterators","tag-iterators-terminating-on-the-shortest-input-sequence","tag-python-iterables","tag-python-iterators","tag-python-itertools"],"yoast_head":"\n\n
Infinite Iterators in Python<\/h3>\n
1. count([start=0, step=1]) in Python<\/h4>\n
>>> from itertools import count\r\n>>> for i in count(10,2):\r\n print(i)\r\n if i>25: break<\/pre>\n
\n12
\n14
\n16
\n18
\n20
\n22
\n24
\n26<\/div>\n>>> for i in count(2):\r\n print(i)\r\n<\/pre>\n
\n3
\n4
\n5
\n6
\n7
\nTraceback (most recent call last):File “<pyshell#166>”, line 2, in <module>
\nprint(i)
\nKeyboardInterrupt<\/div>\n>>> for i in count():\r\n print(i)\r\n<\/pre>\n
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15
\nTraceback (most recent call last):File “<pyshell#169>”, line 2, in <module>
\nprint(i)
\nKeyboardInterrupt<\/div>\n2. cycle(iterable) in Python<\/h4>\n
>>> from itertools import cycle\r\n>>> for i in cycle(['red','green','blue']):\r\n print(i)\r\n<\/pre>\n
\ngreen
\nblue
\nred
\ngreen
\nblue
\nred
\ngreen
\nblue
\nred
\ngreen
\nblue
\nred
\ngreen
\nblue
\nTraceback (most recent call last):File “<pyshell#174>”, line 2, in <module>
\nprint(i)
\n<KeyboardInterrupt<\/div>\n<\/pre>\n
3. repeat(elem [,n]) in Python<\/h4>\n
>>> from itertools import repeat\r\n>>> for i in repeat(\u2018Red\u2019,3):\r\n print(i)\r\n<\/pre>\n
\nRed
\nRed<\/div>\n>>> for i in repeat('Red'):\r\n print(i)<\/pre>\n
\nRed
\nRed
\nRed
\nRed
\nRed
\nRed
\nRed
\nRed
\nRed
\nRed
\nRed
\nRed
\nRed
\nTraceback (most recent call last):File “<pyshell#181>”, line 2, in <module>
\nprint(i)
\nKeyboardInterrupt<\/div>\nCombinatoric Iterators in Python<\/h3>\n
1. product(*iterables, repeat=1) in Python<\/h4>\n
>>> for i in product([1,2,3],[4,5,6]):\r\n print(i)<\/pre>\n
\n(1, 5)
\n(1, 6)
\n(2, 4)
\n(2, 5)
\n(2, 6)
\n(3, 4)
\n(3, 5)
\n(3, 6)<\/div>\n>>> for i in ((i,j) for i in [1,2,3] for j in [4,5,6]):\r\n print(i)<\/pre>\n
\n(1, 5)
\n(1, 6)
\n(2, 4)
\n(2, 5)
\n(2, 6)
\n(3, 4)
\n(3, 5)
\n(3, 6)<\/div>\n>>> for i in product('AB','CD','EF'):\r\n print(i)<\/pre>\n
\n(‘A’, ‘C’, ‘F’)
\n(‘A’, ‘D’, ‘E’)
\n(‘A’, ‘D’, ‘F’)
\n(‘B’, ‘C’, ‘E’)
\n(‘B’, ‘C’, ‘F’)
\n(‘B’, ‘D’, ‘E’)
\n(‘B’, ‘D’, ‘F’)<\/div>\n>>> for i in product('AB','CD',repeat=2):\r\n print(i)<\/pre>\n
\n(‘A’, ‘C’, ‘A’, ‘D’)
\n(‘A’, ‘C’, ‘B’, ‘C’)
\n(‘A’, ‘C’, ‘B’, ‘D’)
\n(‘A’, ‘D’, ‘A’, ‘C’)
\n(‘A’, ‘D’, ‘A’, ‘D’)
\n(‘A’, ‘D’, ‘B’, ‘C’)
\n(‘A’, ‘D’, ‘B’, ‘D’)
\n(‘B’, ‘C’, ‘A’, ‘C’)
\n(‘B’, ‘C’, ‘A’, ‘D’)
\n(‘B’, ‘C’, ‘B’, ‘C’)
\n(‘B’, ‘C’, ‘B’, ‘D’)
\n(‘B’, ‘D’, ‘A’, ‘C’)
\n(‘B’, ‘D’, ‘A’, ‘D’)
\n(‘B’, ‘D’, ‘B’, ‘C’)
\n(‘B’, ‘D’, ‘B’, ‘D’)<\/div>\n2. permutations(iterable,r=None) in Python<\/h4>\n
>>> from itertools import permutations\r\n>>> for i in permutations('ABCD'):\r\n print(i)<\/pre>\n
\n(‘A’, ‘B’, ‘D’, ‘C’)
\n(‘A’, ‘C’, ‘B’, ‘D’)
\n(‘A’, ‘C’, ‘D’, ‘B’)
\n(‘A’, ‘D’, ‘B’, ‘C’)
\n(‘A’, ‘D’, ‘C’, ‘B’)
\n(‘B’, ‘A’, ‘C’, ‘D’)
\n(‘B’, ‘A’, ‘D’, ‘C’)
\n(‘B’, ‘C’, ‘A’, ‘D’)
\n(‘B’, ‘C’, ‘D’, ‘A’)
\n(‘B’, ‘D’, ‘A’, ‘C’)
\n(‘B’, ‘D’, ‘C’, ‘A’)
\n(‘C’, ‘A’, ‘B’, ‘D’)
\n(‘C’, ‘A’, ‘D’, ‘B’)
\n(‘C’, ‘B’, ‘A’, ‘D’)
\n(‘C’, ‘B’, ‘D’, ‘A’)
\n(‘C’, ‘D’, ‘A’, ‘B’)
\n(‘C’, ‘D’, ‘B’, ‘A’)
\n(‘D’, ‘A’, ‘B’, ‘C’)
\n(‘D’, ‘A’, ‘C’, ‘B’)
\n(‘D’, ‘B’, ‘A’, ‘C’)
\n(‘D’, ‘B’, ‘C’, ‘A’)
\n(‘D’, ‘C’, ‘A’, ‘B’)
\n(‘D’, ‘C’, ‘B’, ‘A’)<\/div>\n>>> for i in permutations('ABCD',3):\r\n print(i)\r\n<\/pre>\n
\n(‘A’, ‘B’, ‘D’)
\n(‘A’, ‘C’, ‘B’)
\n(‘A’, ‘C’, ‘D’)
\n(‘A’, ‘D’, ‘B’)
\n(‘A’, ‘D’, ‘C’)
\n(‘B’, ‘A’, ‘C’)
\n(‘B’, ‘A’, ‘D’)
\n(‘B’, ‘C’, ‘A’)
\n(‘B’, ‘C’, ‘D’)
\n(‘B’, ‘D’, ‘A’)
\n(‘B’, ‘D’, ‘C’)
\n(‘C’, ‘A’, ‘B’)
\n(‘C’, ‘A’, ‘D’)
\n(‘C’, ‘B’, ‘A’)
\n(‘C’, ‘B’, ‘D’)
\n(‘C’, ‘D’, ‘A’)
\n(‘C’, ‘D’, ‘B’)
\n(‘D’, ‘A’, ‘B’)
\n(‘D’, ‘A’, ‘C’)
\n(‘D’, ‘B’, ‘A’)
\n(‘D’, ‘B’, ‘C’)
\n(‘D’, ‘C’, ‘A’)
\n(‘D’, ‘C’, ‘B’)<\/div>\n3. combinations(iterable,r) in Python<\/h4>\n
>>> from itertools import combinations\r\n>>> for i in combinations('ABCD',2):\r\n print(i)<\/pre>\n
\n(‘A’, ‘C’)
\n(‘A’, ‘D’)
\n(‘B’, ‘C’)
\n(‘B’, ‘D’)
\n(‘C’, ‘D’)<\/div>\n>>> for i in combinations(range(4),3):\r\n print(i)<\/pre>\n
\n(0, 1, 3)
\n(0, 2, 3)
\n(1, 2, 3)<\/div>\n4. combinations_with_replacement(iterable, r) in Python<\/h4>\n
>>> from itertools import combinations_with_replacement as cwr\r\n>>> for i in cwr('ABCD',2):\r\n print(i)<\/pre>\n
\n(‘A’, ‘B’)
\n(‘A’, ‘C’)
\n(‘A’, ‘D’)
\n(‘B’, ‘B’)
\n(‘B’, ‘C’)
\n(‘B’, ‘D’)
\n(‘C’, ‘C’)
\n(‘C’, ‘D’)
\n(‘D’, ‘D’)<\/div>\nIterators Terminating on the Shortest Input Sequence<\/h3>\n
1. accumulate(iterable [,func]) in Python<\/h4>\n
>>> from itertools import accumulate\r\n>>> for i in accumulate([0,1,0,1,1,2,3,5]):\r\n print(i)<\/pre>\n
\n1
\n2
\n3
\n5
\n8
\n13<\/div>\n>>> import operator\r\n>>> for i in accumulate([1,2,3,4,5],operator.mul):\r\n print(i)<\/pre>\n
\n2
\n6
\n24
\n120<\/div>\n>>> for i in accumulate([2,1,4,3,5],max):\r\n print(i)<\/pre>\n
\n2
\n4
\n4
\n5<\/div>\n2. chain(*iterables) in Python<\/h4>\n
>>> from itertools import chain\r\n>>> for i in chain('Hello','World','Bye'):\r\n print(i)<\/pre>\n
\ne
\nl
\nl
\no
\nW
\no
\nr
\nl
\nd
\nB
\ny
\ne<\/div>\n3. chain.from_iterable(iterable) in Python<\/h4>\n
>>> for i in chain.from_iterable(['Hello','World','Bye']):\r\n print(i)<\/pre>\n
\ne
\nl
\nl
\no
\nW
\no
\nr
\nl
\nd
\nB
\ny
\ne<\/div>\n4. compress(data, selectors) in Python<\/h4>\n
>>> from itertools import compress\r\n>>> for i in compress('ABCDEF',[1,0,1,True,0,' ']):\r\n print(i)<\/pre>\n
\nC
\nD
\nF<\/div>\n5. dropwhile(predicate,iterable) in Python<\/h4>\n
>>> from itertools import dropwhile\r\n>>> for i in dropwhile(lambda x:x<7,[1,2,7,9,5,3,2,9]):\r\n print(i)<\/pre>\n
\n9
\n5
\n3
\n2
\n9<\/div>\n6. filterfalse(predicate,iterable) in Python<\/h4>\n
>>> from itertools import filterfalse\r\n>>> for i in filterfalse(lambda x:x<7,[1,2,7,9,5,3,2,9]):\r\n print(i)<\/pre>\n
\n9
\n9<\/div>\n>>> for i in filterfalse(lambda x:x%2,[1,2,7,9,5,3,2,9]):\r\n print(i)<\/pre>\n
\n2<\/div>\n7. groupby(iterable,key=None) in Python<\/h4>\n
>>> from itertools import groupby\r\n>>> for i,j in groupby('AAAAABBCCCCCDDDCCCBBA'):\r\n print(list(j))<\/pre>\n
\n[‘B’, ‘B’]
\n[‘C’, ‘C’, ‘C’, ‘C’, ‘C’]
\n[‘D’, ‘D’, ‘D’]
\n[‘C’, ‘C’, ‘C’]
\n[‘B’, ‘B’]
\n[‘A’]<\/div>\n8. islice(iterable,stop) in Python<\/h4>\n
>>> from itertools import islice\r\n>>> for i in islice([1,2,3,4,5],2):\r\n print(i)<\/pre>\n
\n2<\/div>\n>>> for i in islice([1,2,3,4,5],2,5):\r\n print(i)<\/pre>\n
\n4
\n5<\/div>\n>>> for i in islice([1,2,3,4,5],0,5,2):\r\n print(i)\r\n<\/pre>\n
\n3
\n5<\/div>\n9. starmap(function,iterable) in Python<\/h4>\n
>>> from itertools import starmap\r\n>>> for i in starmap(operator.sub,[(2,1),(7,3),(15,10)]):\r\n print(i)<\/pre>\n
\n4
\n5<\/div>\n10. takewhile(predicate,iterable) in Python<\/h4>\n
>>> from itertools import takewhile\r\n>>> for i in takewhile(lambda x:x<7,[1,2,7,9,5,3,2,9]):\r\n print(i)<\/pre>\n
\n2<\/div>\n11. tee(n=2) in Python<\/h4>\n
>>> from itertools import tee\r\n>>> for i in tee([1,2,3,4,5,6,7],3):\r\n for j in i: print(j)\r\n print()<\/pre>\n
\n2
\n3
\n4
\n5
\n6
\n71
\n2
\n3
\n4
\n5
\n6
\n71
\n2
\n3
\n4
\n5
\n6
\n7<\/div>\n12. zip_longest(*iterables,fillvalue=None) in Python<\/h4>\n
>>> from itertools import zip_longest\r\n>>> for i in zip_longest('ABC','12345',fillvalue='*'):\r\n print(i)<\/pre>\n
\n(‘B’, ‘2’)
\n(‘C’, ‘3’)
\n(‘*’, ‘4’)
\n(‘*’, ‘5’)<\/div>\n>>> for i in zip_longest('ABC','12345','Hello',fillvalue='*'):\r\n print(i)<\/pre>\n
\n(‘B’, ‘2’, ‘e’)
\n(‘C’, ‘3’, ‘l’)
\n(‘*’, ‘4’, ‘l’)
\n(‘*’, ‘5’, ‘o’)<\/div>\nPython Interview Questions on Itertools<\/h3>\n
Conclusion<\/h3>\n