Binary to decimal convertion error

Question

I want to solve function >> y=-2^x
But this metod down here shows values that are very strange for me :D
I know that that its caused by that python in binary nubers cant save nubers like 9.9 9.8 etc...
Do you know any method how to have clean results?

a=-10.0
for i in range (201):
print("-2^",a,"=",(-2)**a)
a+=0.1

Answer 1

So...this is all new to me but I've been picking up on the abundance of hints here related to float storage. And that's a disclaimer to verify; yourself.

Floats aren't precise. Decimals are, but they're immutable. It looks like this works:

>>> from decimal import *
>>> a = Decimal('-10.0')
>>> a += Decimal('0.1')
>>> a
Decimal('-9.9')
>>> 2**-9.9
0.0010466537720080985
>>> 2**a
Decimal('0.001046653772008098793176763989')

Answer 2

Now i know why it output so terrible outputs, because you cant power minus numbers with float