Underflow occurs when an operation results in a rational number that falls into the gap at zero; see Figure 2.1.
The machine epsilon, or rounding unit, is the largest number 
such that 
.
Note that 
on most of today's computers. The value that applies on the actual machine you are running your code on is accessible using the following command:
import sys
sys.float_info.epsilon # 2.220446049250313e-16
The variable sys.float_info contains more information on the internal representation of the float type on your machine.
The function float converts other types to a floating-point number, if possible. This function is especially useful when converting an appropriate string to a number:
a = float('1.356')
