61 lines
2.9 KiB
Markdown
61 lines
2.9 KiB
Markdown
---
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title: Itertools
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---
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Itertools is a python module of functions that return generators, objects that only function when iterated over.
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Some examples of itertool functions include but not limited to: chain(), imap(), product(), and compress().
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### chain()
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The chain() function takes several iterators as arguments and returns a single iterator that produces the contents of all of them as though they came from one sequence.
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```py
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import itertools
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list(itertools.chain([1, 2], [3, 4]))
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# Output
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# [1, 2, 3, 4]
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```
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### islice()
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The islice() function returns an iterator which returns selected items from the input iterator, by index. It takes the same arguments as the slice operator for lists: start, stop, and step. Start and stop are optional.
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```py
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import itertools
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list(itertools.islice(count(), 5))
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# Output
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# [0,1, 2, 3, 4]
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```
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### izip()
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izip() returns an iterator that combines the elements of several iterators into tuples. It works like the built-in function zip(), except that it returns an iterator instead of a list.
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```py
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import itertools
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list(izip([1, 2, 3], ['a', 'b', 'c']))
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# Output
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# [(1, 'a'),(2, 'b'),(3, 'c')]
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```
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Combinatoric iterators:
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Iterator Arguments Results
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product() p, q, … [repeat=1] cartesian product, equivalent to a nested for-loop
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permutations() p[, r] r-length tuples, all possible orderings, no repeated elements
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combinations() p, r r-length tuples, in sorted order, no repeated elements
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combinations_with_replacement() p, r r-length tuples, in sorted order, with repeated elements
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product('ABCD', repeat=2) AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD
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permutations('ABCD', 2) AB AC AD BA BC BD CA CB CD DA DB DC
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combinations('ABCD', 2) AB AC AD BC BD CD
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combinations_with_replacement('ABCD', 2) AA AB AC AD BB BC BD CC CD DD
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Source:https://docs.python.org/3/library/itertools.html |