Source: 📖 Effective Python item 72

Using bisect

Using the bisect module can dramatically increase the speed of searching through an ordered list or other containers. bisect is a binary search algorithm, meaning that runtime increases logarithmically (O(log N)) as the size of the data set increases. Compared to a linear search algorithm (iterating through every list item using a for loop) whose runtime increases linearly, the bisect module can significantly improve performance.

from bisect import bisect_left

data = list(range(10**5))		# list of 100k items

index = bisect_left(data, 91234)		# find the index position of the number 91234
print(index)

>>>
91234			# returns the correct index