Answer by Daniel Stutzbach for Checking if float is equivalent to an integer value in python

Under the hood, Python's float type is a C double.

The most robust way would be to get the nearest integer to num, then test if that integers satisfies the property you're after:

import mathdef is_triangular1(x):    num = (1/2) * (math.sqrt(8*x+1)-1 )    inum = int(round(num))    return inum*(inum+1) == 2*x  # This line uses only integer arithmetic