Most languages have a NaN constant you can use to assign a variable the value NaN. Can python do this without using numpy?
A more consistent (and less opaque) way to generate inf and -inf is to again use float():
>> positive_inf = float('inf')
>> positive_inf
inf
>> negative_inf = float('-inf')
>> negative_inf
-inf
Note that the size of a float varies depending on the architecture, so it probably best to avoid using magic numbers like 9e999, even if that is likely to work.
import sys
sys.float_info
sys.float_info(max=1.7976931348623157e+308,
max_exp=1024, max_10_exp=308,
min=2.2250738585072014e-308, min_exp=-1021,
min_10_exp=-307, dig=15, mant_dig=53,
epsilon=2.220446049250313e-16, radix=2, rounds=1)