Python idiom to return first item or None

Question

I\'m sure there\'s a simpler way of doing this that\'s just not occurring to me.

I\'m calling a bunch of methods that return a list. The list may be empty. If the

Answer 1

You could use Extract Method. In other words extract that code into a method which you'd then call.

I wouldn't try to compress it much more, the one liners seem harder to read than the verbose version. And if you use Extract Method, it's a one liner ;)

Answer 2

isn't the idiomatic python equivalent to C-style ternary operators

cond and true_expr or false_expr

ie.

list = get_list()
return list and list[0] or None

Answer 3

if mylist != []:

       print(mylist[0])

   else:

       print(None)

Answer 4

If you find yourself trying to pluck the first thing (or None) from a list comprehension you can switch to a generator to do it like:

next((x for x in blah if cond), None)

Pro: works if blah isn't indexable Con: it's unfamiliar syntax. It's useful while hacking around and filtering stuff in ipython though.

Answer 5

Regarding idioms, there is an itertools recipe called nth.

From itertools recipes:

def nth(iterable, n, default=None):
    "Returns the nth item or a default value"
    return next(islice(iterable, n, None), default)

If you want one-liners, consider installing a library that implements this recipe for you, e.g. more_itertools:

import more_itertools as mit

mit.nth([3, 2, 1], 0)
# 3

mit.nth([], 0)                                             # default is `None`
# None

Another tool is available that only returns the first item, called more_itertools.first.

mit.first([3, 2, 1])
# 3

mit.first([], default=None)
# None

These itertools scale generically for any iterable, not only for lists.

Answer 6

Frankly speaking, I do not think there is a better idiom: your is clear and terse - no need for anything "better". Maybe, but this is really a matter of taste, you could change if len(list) > 0: with if list: - an empty list will always evaluate to False.

On a related note, Python is not Perl (no pun intended!), you do not have to get the coolest code possible.
Actually, the worst code I have seen in Python, was also very cool :-) and completely unmaintainable.

By the way, most of the solution I have seen here do not take into consideration when list[0] evaluates to False (e.g. empty string, or zero) - in this case, they all return None and not the correct element.