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| Itertools |
Itertools is a python module of functions that return generators, objects that only function when iterated over. Some examples of itertool functions include but not limited to: chain(), imap(), product(), and compress().
chain()
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.
import itertools
list(itertools.chain([1, 2], [3, 4]))
# Output
# [1, 2, 3, 4]
islice()
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.
import itertools
list(itertools.islice(count(), 5))
# Output
# [0,1, 2, 3, 4]
izip()
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.
import itertools
list(izip([1, 2, 3], ['a', 'b', 'c']))
# Output
# [(1, 'a'),(2, 'b'),(3, 'c')]
Combinatoric iterators:
Iterator Arguments Results product() p, q, … [repeat=1] cartesian product, equivalent to a nested for-loop permutations() p[, r] r-length tuples, all possible orderings, no repeated elements combinations() p, r r-length tuples, in sorted order, no repeated elements combinations_with_replacement() p, r r-length tuples, in sorted order, with repeated elements product('ABCD', repeat=2) AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD permutations('ABCD', 2) AB AC AD BA BC BD CA CB CD DA DB DC
combinations('ABCD', 2) AB AC AD BC BD CD
combinations_with_replacement('ABCD', 2) AA AB AC AD BB BC BD CC CD DD