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itertools.dropwhile

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itertools.dropwhile enables you to take items from a sequence after a condition first becomes False. 

def is_even(x):
    return x % 2 == 0

lst = [0, 2, 4, 12, 18, 13, 14, 22, 23, 44]
result = list(itertools.dropwhile(is_even, lst))

print(result)

This outputs [13, 14, 22, 23, 44].

(This example is same as the example for takewhile but using dropwhile.)

Note that, the first number that violates the predicate (i.e.: the function returning a Boolean value) is_even is, 13. All the elements before that, are discarded.

The output produced by dropwhile is similar to the output generated from the code below. 

def dropwhile(predicate, iterable):
	iterable = iter(iterable)
	for x in iterable:
		if not predicate(x):
			yield x
		break
	for x in iterable:
		yield x

The concatenation of results produced by takewhile and dropwhile produces the original iterable.

result = list(itertools.takewhile(is_even, lst)) + list(itertools.dropwhile(is_even, lst))

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Itertools Module:
* Itertools Module
* itertools.dropwhile
* Combinations method in Itertools Module
* Take a slice of a generator
* Zipping two iterators until they are both exhausted
* Grouping items from an iterable object using a function
* itertools.takewhile
* itertools.count
* itertools.product
* itertools.repeat
* Get an accumulated sum of numbers in an iterable
* Cycle through elements in an iterator
* itertools.permutations
* Chaining multiple iterators together
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