Check if any item in Python list is None (but include zero)

Question

I'm trying to do a simple test that returns True if any of the results of a list are None. However, I want 0 and '' to not cause a return of True.

list_1 = [0, 1, None, 4] list_2 = [0, 1, 3, 4] any(list_1) is None >>>False any(list_2) is None >>>False

As you can see, the any() function as it is isn't being helpful in this context.

Note that the current code means "if the result of my call to any happens to be None" (which, given that it will return True or False or raise an exception, will never happen). — jonrsharpe
– jonrsharpe, Commented Mar 3, 2015 at 16:09

Martijn Pieters · Accepted Answer · 2015-03-03 16:12:24Z

190

For list objects can simply use a membership test:

None in list_1

Like any(), the membership test on a list will scan all elements but short-circuit by returning as soon as a match is found.

any() returns True or False, never None, so your any(list_1) is None test is certainly not going anywhere. You'd have to pass in a generator expression for any() to iterate over, instead:

any(elem is None for elem in list_1)

edited Mar 3, 2015 at 16:12

answered Mar 3, 2015 at 16:06

Martijn Pieters

1.1m326 gold badges4.2k silver badges3.4k bronze badges

Sign up to request clarification or add additional context in comments.

9 Comments

d6bels Over a year ago

And I'd quote that any Return True if any element of the iterable is true. If the iterable is empty, return False. So that was indeed not the right thing to use

Gareth Latty Over a year ago

@d6bels Not exactly. It's a perfectly natural use case of any(), you just need to combine it with a generator expression. in is fine in this case where list_1 is actually a List - in some cases it might be an arbitrary iterable without __contains__() implemented, and in such cases the any() solution would be the best option.

frankliuao Over a year ago

This will create troubles when the list contains Numpy arrays. Tom Cornebize has a better solution.

Martijn Pieters Over a year ago

@frankliuao: but on numpy arrays you probably want to work with numpy.any() in any case, and not store None objects in a numeric array.

PDiracDelta Over a year ago

Note that this does not work if one of the list elements is a numpy array. In that case, first use list() on the array.

|

Tom Cornebize · Accepted Answer · 2015-03-03 16:08:18Z

list_1 = [0, 1, None, 4] list_2 = [0, 1, 3, 4] any(x is None for x in list_1) >>>True any(x is None for x in list_2) >>>False

Collectives™ on Stack Overflow

Check if any item in Python list is None (but include zero)

2 Answers 2

9 Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

9 Comments

Comments

Linked

Related