import math


def _isnan(value):
    """Check if a value is NaN.

    This differs from ``math.isnan`` in that **any** input type is
    allowed.

    Args:
        value (Any): A value to check for NaN-ness.

    Returns:
        bool: Indicates if the value is the NaN float.
    """
    if isinstance(value, float):
        return math.isnan(value)
    else:
        return False