"""
A triangular number or triangle number counts objects arranged in an
equilateral triangle. This module provides a function to generate n'th
triangular number.
For more information about triangular numbers, refer to:
https://en.wikipedia.org/wiki/Triangular_number
"""
def triangular_number(position: int) -> int:
"""
Generate the triangular number at the specified position.
Args:
position (int): The position of the triangular number to generate.
Returns:
int: The triangular number at the specified position.
Raises:
ValueError: If `position` is negative.
Examples:
>>> triangular_number(1)
1
>>> triangular_number(3)
6
>>> triangular_number(-1)
Traceback (most recent call last):
...
ValueError: param `position` must be non-negative
"""
if position < 0:
raise ValueError("param `position` must be non-negative")
return position * (position + 1) // 2
if __name__ == "__main__":
import doctest
doctest.testmod()