Diffrence of two same values is not zero

Question

When I compare two numbers at python, even though they are exactly the same, the difference between these two numbers is not zero, but something really small (<10^(-16)).

e.g.

if A == B:
    print('We are the same')

Nothing happens. But:

if A - B < 10^(-16):
    print(A-B)

It prints the difference.

Where is the problem?

this question is not a duplicate of [Is floating point math broken?](https://stackoverflow.com/questions/588004/is-floating-point-math-broken) — Gsk, Dec 20 '18 at 11:56
What are the exact values of `A` and `B`? Please show a [Minimal Complete Verifiable Example](https://stackoverflow.com/help/mcve). — Eric Postpischil, Dec 20 '18 at 13:39

score 2 · Answer 1 · answered Dec 20 '18 at 13:55

in Python, the ^ operator execute an exclusive or, so 10^(-16) means 10 XOR (-16), which correctly returns -6 (which is lower than A-B).
If you wanted to execute an exponentiation, you have to write 10**(-16), and your check is now working as expected.

This means that your code should be:

if A - B < 10**(-16):
    print(A-B)

# OUTPUT: 0

Diffrence of two same values is not zero

1 Answers1