We start from the simplest way to write a Python program. The formula of estimating the present value for a given future cash flow is as follows:

In this equation, PV is the present value FV is the future value R is the periodic discount rate, and n is the number of periods. After launching Python, we just type the following two lines. After typing the second line, press the Enter key on our keyboard twice to return to the Python prompt of >>>:

>>>def pv_f(pv,r,n):
             return fv/(1+r)**n
>>>

The key word used to write a Python function is def. The function name is pv_f. The input variables are enclosed in the parentheses. Notice that upon pressing the Enter key after we type colon (:), the next line is automatically indented. Now, we are ready to call this present value function easily just as any Python built-in function. One of the wonderful features is that after typing the function name and the left parenthesis...