How Do You Display a Fixed Number of Numbers after the Decimal Point in Python?

Problem scenario
You want to display a specific number of places after the decimal (e.g., one, two or three) with numeric values in Python. You want the decimal value to be rounded if it is too long. How do you always show (including trailing zeroes) a specific number of places to the right of the decimal point?

Solution
This Python 3 program will illustrate how:

x=123.45678
y="{:.3f}".format(x)
print(y)

a=123
b="{:.1f}".format(a)
print(b)