Final answer:
To display the number '12.987654' as '12.988', use the format string '{:0.3f}'. This will round the number to three decimal places when using Python's format() method.
Step-by-step explanation:
To format the number 12.987654 to display as '12.988', you need to round it to three decimal places. The format string in Python uses the format() method, where the placeholder inside curly braces {} can be customized to dictate how the number is formatted. It includes the overall width, the number of decimal places, and other formatting options.
In this case, to achieve the desired output with three decimal places, you should use 0.3f within the curly braces. This means that you're formatting a floating-point number with three digits after the decimal point. Hence, the complete format string should be '{:0.3f}'.format(12.987654).