A Concise Introduction to Programming in Python

Chapter 9

Computer Memory: Floats

Predict what this code will do when it runs:

x = 0

while x != 1:

print(x)

x += 0.1

Then run it. Are you surprised? Ctrl-C, in case you have forgotten.

What is going on here? Isn’t 0.1 the same as 1/10?

The explanation is subtle, but it affects every floating-point computer program

in the world, including some used in life-or-death situations. The basic issue

is that, like integers, floating-p oint numbers are stored in binary rather than

decimal form.

Binary Fractions

In base ten, you are familiar with the fact that 1/3 has an infinitely-repeating

decimal form, 0.33333333 . . .. If we used base ten computers, you would prob-