Both functions return the absolute value of a number by ignoring its sign. However, abs() is a built-in function and doesn't need any library / module to be loaded. The fabs() function on the other hand is defined in math module, hence the same must be imported before using.
>>> abs(-45) 45 >>> abs(110.12) 110.12 >>> import math >>> math.fabs(-45) 45.0 >>> math.fabs(110.12) 110.12