Check if list contains only item x

Question

Say all of w, x, y, and z can be in list A. Is there a shortcut for checking that it contains only x--eg. without negating the other variables?

w, x, y, and z are all single values (not lists, tuples, etc).

Just to be clear, by "all single values", do you mean things like `int` and `float` and `str`ings, or could (e.g.) `y` be a `list`? — DSM, Aug 31 '12 at 21:37
Wait- do you mean that it doesn't include w, y, or z but can include other variables (let's say a, b, or c?) — David Robinson, Aug 31 '12 at 21:43

gefei · Accepted Answer · 2012-08-31T21:40:39.410

31

A=[w,y,x,z]
all(p == x for p in A)

edited Aug 31 '12 at 21:40

answered Aug 31 '12 at 21:35

gefei

18,124
7
49
65

3

Be careful: if list is empty, the expression always evaluates to `True`- although `x` is not in the list. If the list may be empty, use `all(p == x for p in A) and len(A) > 0` – Mesa Aug 24 '18 at 12:27
Would be helpful if you could make in an example with both Lists, I can't understand that code at all – eliezra236 Nov 07 '21 at 18:57

score 20 · Answer 2 · edited Jul 29 '19 at 07:36

20

That, or if you don't want to deal with a loop:

>>> a = [w,x,y,z]
>>> a.count(x) == len(a) and a

(and a is added to check against empty list)

edited Jul 29 '19 at 07:36

Jean-François Fabre

131,796
23
122
195

answered Aug 31 '12 at 22:21

Eric Hulser

3,794
19
20

I found this method to be 5 times faster than the accepted answer. – Jonas K May 29 '13 at 08:31
Very cool, pythonic answer. And apparently faster too. – Rithwik Jul 29 '21 at 14:18

Claudiu · Answer 3 · 2012-08-31T21:48:34.857

4

This checks that all elements in A are equal to x without reference to any other variables:

all(element==x for element in A)

edited Aug 31 '12 at 21:48

answered Aug 31 '12 at 21:38

Claudiu

216,039
159
467
667

I think it can include multiple x's – David Robinson Aug 31 '12 at 21:38

score 4 · Answer 4 · answered Aug 31 '12 at 21:39

4

If all items in the list are hashable:

set(A) == set([x])

answered Aug 31 '12 at 21:39

David Robinson

74,512
15
159
179

this is a bit inefficient as you have to compute the set instead of just iterating through `A` once – Claudiu Aug 31 '12 at 21:47
In newer versions you can use `{x}` sugar. – sdcvvc Sep 05 '12 at 08:58

score 4 · Answer 5 · answered Aug 31 '12 at 21:40

4

{x} == {w,x,y,z} & set(A)

This will work if all of [w,x,y,z] and items in A are hashable.

answered Aug 31 '12 at 21:40

Alexey Kachayev

5,956
26
24

score 1 · Answer 6 · answered Aug 31 '12 at 21:39

1

I'm not sure what without negating the other variables means, but I suspect that this is what you want:

if all(item == x for item in myList): 
    #do stuff

answered Aug 31 '12 at 21:39

Chinmay Kanchi

58,811
22
84
113

score 1 · Answer 7 · answered Aug 31 '12 at 21:56

1

Heres another way:

>>> [x] * 4 == [x,w,z,y]

of the many already stated.

answered Aug 31 '12 at 21:56

Samy Vilar

10,109
2
34
33

the wolf · Answer 8 · 2012-08-31T22:13:06.510

0

There are two interpretations to this question:

First, is the value of x contained in [w,y,z]:

>>> w,x,y,z=1,2,3,2
>>> any(x == v for v in [w,y,z])
True
>>> w,x,y,z=1,2,3,4
>>> any(x == v for v in [w,y,z])
False

Or it could mean that they represent the same object:

>>> w,x,y,z=1,2,3,4
>>> any(x is v for v in [w,y,z])
False
>>> w,x,y,z=1,2,3,x
>>> any(x is v for v in [w,y,z])
True

edited Aug 31 '12 at 22:13

answered Aug 31 '12 at 21:57

the wolf

32,251
12
52
71

Check if list contains only item x

8 Answers8

Linked

Related