Your first Python program

Learning objectives

• Describe a problem using input, process, and output.
• Run a Python code cell.
• Use print() to display a result.
• Turn a plain-language algorithm into code.

The pattern

Suppose we want to calculate the total minutes in a school day:

Write the algorithm before the code:

read the number of periods
read the minutes per period
multiply the two values
display the total

Code cell

periods = 6
minutes_per_period = 50
total_minutes = periods * minutes_per_period

print(f"A school day has {total_minutes} class minutes.")

periods and minutes_per_period store input values. The multiplication is the process. The formatted string is the output.

Guided practice

Change the program to calculate:

1. the number of minutes in five periods;
2. the total minutes for a different schedule; and
3. the number of hours represented by the result.

periods = 5
minutes_per_period = 55
total_minutes = periods * minutes_per_period
hours = total_minutes / 60

print(total_minutes)
print(hours)

Checkpoint

Explain why total_minutes is a better name than x. Then write an input-process-output plan for a program that calculates the cost of three notebooks.

Mini-project

Build a unit converter that converts kilometers to miles. State the conversion assumption in a comment and test the program with zero and a larger value.