US_population_program.py

#US_population_Program.py
# Similar to Assignment 2 Project 2: Fitness Tracker Project with a Console Interface
# The program assumes that all population changes are positive.
# That is, that each year the population was larger than the
# previous year.

def main():
    # Setup variables
    yearly_change = []
    change = 0.0
    total_change = 0.0
    average_change = 0.0
    greatest_increase = 0.0
    smallest_increase = 0.0
    greatest_year = 0
    smallest_year = 0

    # Constant for the base year
    BASE_YEAR = 1950

    try:
        # Open the file for reading.
        input_file = open('USPopulation.txt', 'r')

        # Read all the lines in the file into a list.
        yearly_population = input_file.readlines()

        # Turn all read strings into numbers.
        for i in range(len(yearly_population)):
            yearly_population[i] = float(yearly_population[i])

        # Calculate the change in population size for each two years.
        for i in range(1, len(yearly_population)):
            change = yearly_population[i] - yearly_population[i - 1]
            yearly_change.append(change)

            # If this is the first year, set trackers to its value.
            if i == 1:
                greatest_increase = change
                smallest_increase = change
                greatest_year = 1
                smallest_year = 1

            # This is not the first change in population size.
            # Update trackers if relevant.
            else:
                if change > greatest_increase:
                    greatest_increase = change
                    greatest_year = i

                elif change < smallest_increase:
                    smallest_increase = change
                    smallest_year = i

        total_change = float(sum(yearly_change))
        average_change = total_change / len(yearly_change)

        print('The average annual change in population ' \
              'during the time period is', format(average_change, ',.2f'))
        print('The year with the greatest increase in population was', \
              BASE_YEAR + greatest_year)
        print('The year with the smallest increase in population was', \
              BASE_YEAR + smallest_year)

    except IOError:
        print('The file could not be found.')
    except IndexError:
        print('There was an indexing error.')
    except:
        print('An error occurred.')


# Call the main function.
main()