Binary search - find the first position

binary_search_first_position.py

def find_first_pos(arr, target):
    left = 0
    right = len(arr) - 1

    first_position = -1     # keep track of the latest valid mid position
    while left <= right:
        mid = left + (right - left) // 2
        if arr[mid] == target:
            first_position = mid
            right = mid - 1     # continue searching to the left
        elif arr[mid] < target:
            left = mid + 1
        else:
            right = mid - 1

    return first_position