list.index

s.index(x[, i[, j]]) return smallest k such that s[k] == x and `i <= k < j`

Raises ValueError when x is not found in s. When a negative index is passed as the second or third parameter to the [[list.index] method, the list length is added, as for slice indices. If it is still negative, it is truncated to zero, as for slice indices.

Changed in version 2.3: Previously, list.index didn’t have arguments for specifying start and stop positions.