nan

Python has NaN float value and it's a rule-breaking thing:

import math

sorted([5.0, math.nan, 10.0, 0.0])
# [5.0, nan, 0.0, 10.0]

3 < math.nan
# False
3 > math.nan
# False

min(3, math.nan)
# 3
min(math.nan, 3)
# nan

Be careful. Use math.isnan to check if a value is NaN.