python infinity and nan

infinity.py

# coding=utf-8
import math

# +Infinity
positive_inf = float('inf')
# -Infinity
negative_inf = float('-inf')
# Nan
nan = float('nan')

# 比較してみる
print positive_inf == positive_inf
# => True
print negative_inf == negative_inf
# => True
print nan == nan
# False
# nanはいかなる値と比較してもFalseになる

# 検査用の関数
print math.isnan(nan)
# => True
print math.isinf(positive_inf)
# => True
print math.isinf(negative_inf)
# => True