Fastest way to check if a value exist in a list

manpreet Best Answer 2 years ago

I'm searching for the fastest way to know if a value exists in a list (a list with millions of values in it) and what its index is? I know that all values in the list are unique as in this example.

The first method I try is (3.8sec in my real code):

a = [4,2,3,1,5,6]

if a.count(7) == 1:
    b=a.index(7)
    "Do something with variable b"

The second method I try is (2x faster:1.9sec on my real code):

a = [4,2,3,1,5,6]

try:
    b=a.index(7)
except ValueError:
    "Do nothing"
else:
    "Do something with variable b"

Proposed methods from Stackoverflow user (2.74sec on my real code):

a = [4,2,3,1,5,6]
if 7 in a:
    a.index(7)

In my real code, the first method takes 3.81sec and the second method takes 1.88sec. It's a good improvement but:

I'm a beginner with Python/scripting and I want to know if a faster way exists to do the same things and save more processing time?

More specific explication for my application:

In the blender API I can access a list of particles:

particles = [1,2,3,4...etc.]

From there, I can access a particle's location:

particles[x].location = [x,y,z]

And for each particle I test if a neighbour exists by searching each particle location like so:

if [x+1,y,z] in particles.location
    "find the identity of this neighbour particle in x:the particle's index 
    in the array"
    particles.index([x+1,y,z])

manpreet 2 years ago

7 in a