Smallest And Largest Floating Point Values In Python

In my production code, I have a function that calculates a/(a+b). That function threw a ZeroDivisionError at me this afternoon, so I decided to change the equation to a/(a+b+sys.minfloat), because I felt that was more elegant than writing a conditional function to check if (a + b) == 0.

Turns out there is no 'minfloat' in the sys module, so I decided to write a function to calculate the smallest float myself.

>>> def minfloat(guess):
 while(guess * 0.5 != 0):
     guess = guess * 0.5
        return guess

>>> minfloat(+1.0)       # minimum positive value of a float
4.9406564584124654e-324

>>> minfloat(-1.0)      # minimum negative value of a float
-4.9406564584124654e-324

But I couldn't stop there. Now I had to write a function to calculate the largest possible floating point value in Python, just for kicks:

>>> def maxfloat(guess = 1.0):
        while(guess * 2 != guess):
            guess = guess * 2
        return guess

>>> maxfloat(+1.0)       # maximum positive value of a float
inf

>>> maxfloat(-1.0)      # maximum negative value of a float
-inf

This is interesting. Let's find out more about this "inf" value:

>>> inf

Traceback (most recent call last):
  File "", line 1, in 
    inf
NameError: name 'inf' is not defined
>>> float("inf")
inf

>>> inf = maxfloat()

>>> inf + inf
inf

>>> inf - inf
nan

>>> 1 / inf
0.0

>>> 1/(-inf)
-0.0

Finally, check the relationship between minfloat and maxfloat:

>>> 1 / minfloat(1.0)
inf
>>> 1 / minfloat(-1.0)
-inf