Python 2.6+ and Python 3:
If you want StopIteration to be raised if no matching element is found:
next(x for x in the_iterable if x > 3)
If you want default_value (e.g. None) to be returned instead:
next((x for x in the_iterable if x > 3), default_value)
Note that you need an extra pair of parentheses around the generator expression in this case − they are needed whenever the generator expression isn't the only argument.
I see most answers resolutely ignore the next built-in and so I assume that for some mysterious reason they're 100% focused on versions 2.5 and older -- without mentioning the Python-version issue (but then I don't see that mention in the answers that do mention the next built-in, which is why I thought it necessary to provide an answer myself -- at least the "correct version" issue gets on record this way;-).
Python <= 2.5
The .next() method of iterators immediately raises StopIteration if the iterator immediately finishes -- i.e., for your use case, if no item in the iterable satisfies the condition. If you don't care (i.e., you know there must be at least one satisfactory item) then just use .next() (best on a genexp, line for the next built-in in Python 2.6 and better).
If you do care, wrapping things in a function as you had first indicated in your Q seems best, and while the function implementation you proposed is just fine, you could alternatively use itertools, a for...: break loop, or a genexp, or a try/except StopIteration as the function's body, as various answers suggested. There's not much added value in any of these alternatives so I'd go for the starkly-simple version you first proposed.
Python 2.6+ and Python 3:
If you want StopIteration to be raised if no matching element is found:
next(x for x in the_iterable if x > 3)
If you want default_value (e.g. None) to be returned instead:
next((x for x in the_iterable if x > 3), default_value)
Note that you need an extra pair of parentheses around the generator expression in this case − they are needed whenever the generator expression isn't the only argument.
I see most answers resolutely ignore the next built-in and so I assume that for some mysterious reason they're 100% focused on versions 2.5 and older -- without mentioning the Python-version issue (but then I don't see that mention in the answers that do mention the next built-in, which is why I thought it necessary to provide an answer myself -- at least the "correct version" issue gets on record this way;-).
Python <= 2.5
The .next() method of iterators immediately raises StopIteration if the iterator immediately finishes -- i.e., for your use case, if no item in the iterable satisfies the condition. If you don't care (i.e., you know there must be at least one satisfactory item) then just use .next() (best on a genexp, line for the next built-in in Python 2.6 and better).
If you do care, wrapping things in a function as you had first indicated in your Q seems best, and while the function implementation you proposed is just fine, you could alternatively use itertools, a for...: break loop, or a genexp, or a try/except StopIteration as the function's body, as various answers suggested. There's not much added value in any of these alternatives so I'd go for the starkly-simple version you first proposed.
Damn Exceptions!
I love Alex Martelli's answer. However, since next() raise a StopIteration exception when there are no items,
i would use the following snippet to avoid an exception:
a = []
item = next((x for x in a), None)
For example,
a = []
item = next(x for x in a)
Will raise a StopIteration exception;
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration
PEP Proposal: list.first() and list.last() for accessing most important list elements - Ideas - Discussions on Python.org
Select first in for loop
What is the best way to write if first iteration in loop
Here's What I Recommend To ABSOLUTE Beginners
Somewhere I read that learning is a three-legged table:
-
leg 1 is head knowledge -- reading books, watching tutorials and lectures, taking classes, etc.
-
leg 2 is practice -- spending time coding, designing, doing.
-
leg 3 is immersion -- getting into the culture of coding, spending time with people who code talking about coding. Join subreddits, forums, chat rooms, mailing lists. Go to meetups, coding sprints, conventions, etc. So many subtle and oft-overlooked bits of information are picked up this way, and it keeps you in the mindset of coding.
I find a good balance of these things keeps me moving forward as a software developer (or any other discipline I want to learn). Neglect one of these legs and I get stagnant.
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» pip install first
I have code that needs to run specifically in the first time in a loop and i'm wondering whats the best practice / pythonic way of wirting it.
Example:
for i in range(5):
if i == 0:
print("First")
print("normal execution")