Useful Functions: Numeric Functions

Question

Say a number has accuracy upto 18 decimal places. If I try taking round of this number upto 16 decimal places or 17 decimal places, I get the same output and rounded number is upto 15 decimal places. why is that so? Also, say if I want to print the number upto 16 decimal places without rounding it off, what will be the syntax?
===============================
In [82]: x=2.123456789123456789

In [83]: print(round(x,16))
2.123456789123457

In [84]: print(round(x,17))
2.123456789123457
========================

Answer 1

Accuracy of floats is limited as they are exponent-wise stored. So don't be surprised to see your if statements become True when you compare numbers beyond that precision.

More on this:
https://en.m.wikipedia.org/wiki/Floating-point_arithmetic#Accuracy_problems