A pythonic way how to find if a value is between two values in a list

Question

Having a sorted list and some random value, I would like to find in which range the value is.

List goes like this: [0, 5, 10, 15, 20] And value is, say 8.

The standard way would be to either go from start until we hit value that is bigger than ours (like in the example below), or to perform binary search.

grid = [0, 5, 10, 15, 20]
value = 8
result_index = 0
while result_index < len(grid) and grid[result_index] < value:
    result_index += 1

print result_index

I am wondering if there is a more pythonic approach, as this although short, looks bit of an eye sore. Thank you for your time!

Retinol

Answer 1

>>> import bisect
>>> grid = [0, 5, 10, 15, 20]
>>> value = 8
>>> bisect.bisect(grid, value)
2

Edit:

bisect — Array bisection algorithm

Jonellejones

+1, beat me to it by ten seconds. Would be worth linking to the stdlib docs though. – Escapee

i guess i did not find the right terms to search with! Thank you very much, this is exactly what i was looking for! – Retinol

O gosh, another WET language! :) funny to see how python (even though to suffering from a rigid type system as Java) nevertheless forces you to write everything twice. – Commemorative

Adrian, no-one is forcing you to write everything twice. If you intended it to be a joke, I didn't get it; if you meant it, you don't know Python well enough. – Damalus

Answer 2

for min, max in zip(grid, grid[1:]): # [(0, 5), (5, 10), (10, 15), (15, 20), (20, 25)]
  if max <= value < min: #previously: if value in xrange(min, max):
    return min, max
raise ValueError("value out of range")

Journey

What happens if value=2, grid = [3, 2**30] ? – Jonellejones

If your grid is [3, 2**30] chances are you have worse trouble than this. The real problem of this solution is that it only works for integer values of value. – Journey

Point is that generating all the possible values in the range is terribly inefficient compared to value >= min and value <= max. Also, what happens if value=20? – Jonellejones

xrange(15, 20) will yield 15, 16, 17, 18, 19, so the above should return 20, 25. You do raise a point, however. The real corner case is value = 25 where None will be returned. – Journey

Oh, right, 25 is just in badp's example --- I didn't see that. :-) – Jonellejones