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I'm trying to perform checks on the first and last elements of an interator. It has several thousand entries, so I need an expeditious method of checking. If found this post, that put me onto this strategy.
first = True
for value in iterator:
if first:
do_stuff_to_first_iter
first = False
else:
pass
do_stuff_to_last_iter
Anyone have any opinions on a quicker method of accomplishing this? Thanks a lot!
301
To get the last element in an iterator loop you can use std::next() (from C++11). The loop is generally terminated by iterator != container. end() , where end() returns an iterator that points to the past-the-end element.
To get the last element of the list using list. pop(), the list. pop() method is used to access the last element of the list.
The best way to get the last element of a list in Python is using the list[-1]. Python allows you to use negative indices, which count from the end of the list instead of the beginning. So list[-1] gets the last element, list[-2] gets the second to last.
To get the last element of the list in Python, use the list[-1] syntax. The list[-n] syntax gets the nth-to-last element. So list[-1] gets the last element, and list[-2] gets the second to last. The list[-1] is the most preferable, shortest, and Pythonic way to get the last element.
Get the first value with the next() function:
first = last = next(iterable, defaultvalue)
for last in iterable:
pass
This assumes the iterable is finite.
For an empty iterable, first and last are set to defaultvalue. For an iterable with just one element, first and last will both refer to that one element. For any other finite iterable, first will have the first element, last the very last.
109
Based on my answer to the linked question:
Probably worth using __reversed__ if it is available. If you are providing the iterator, and there is a sensible way to implement __reversed__ (ie without iterating from end to end) you should do it
first = last = next(my_iter)
if hasattr(my_iter,'__reversed__'):
last = next(reversed(my_iter))
else:
for last in my_iter:
pass
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