Seven Day Averages

Learning Goals

  • Work with live data
  • Get practice with CSV files and csv.DictReader
  • Practice using dictionaries, lists and exceptions

sevendaysavg

Background

A popular way to track COVID cases is using a 7-day average. Some states only record cases once a week, so using a 7-day average is much more accurate than daily numbers. In this program, you will be using a New York Times repository of live, cumulative COVID data to calculate new daily cases, create a 7-day average, and compare this week’s average to the previous week.

Getting Started

  1. Log into cs50.dev using your GitHub account.
  2. Click inside the terminal window and execute cd.
  3. Execute wget https://cdn.cs50.net/2022/fall/labs/6/seven-day-average.zip followed by Enter in order to download a zip called seven-day-average.zip in your codespace. Take care not to overlook the space between wget and the following URL, or any other character for that matter!
  4. Now execute unzip seven-day-average.zip to create a folder called seven-day-average.
  5. You no longer need the ZIP file, so you can execute rm seven-day-average.zip and respond with “y” followed by Enter at the prompt.

Implementation Details

The distribution code for this problem uses the python requests library to access the New York Times data stored in an accessible GitHub repository. This is stored as a CSV file. The program then uses DictReader to read the CSV file. It then creates a states list to use selected states for calculations.

You will be completing two functions, calculate and comparative_averages.

calculate

In calculate, you’ll be creating a dictionary, new_cases, which will keep track of 14 days of new COVID cases for each state. Keys in this dict will be the names of states, and the values for each of those keys will be the most recent 14 days of new cases. Since the data from the New York Times is cumulative, each day’s new cases must be calculated by subtracting the previous day’s cases. To do this, you may want to create a second dictionary, previous_cases, that keeps track of each day’s new cases as it’s calculated.

  • Hint
    • You can store 14 values in the list for each state by appending each new day’s data to end of the list and when the length of the list is greater than 14, removing the first element from the list.

Your calculate function should ultimately return the new_cases dictionary.

comparative_averages

Since your new_cases dictionary is passed to this function, you can calculate this week’s 7-day average by summing up the last 7 elements in the list for a selected state, then dividing this by 7. You can create a 7-day average for the previous week by doing the same with the first 7 elements in that same list.

  • Hint
    • Check out python list slicing to easily access a range of elements in a list. For example, values[3:5] will return the 3rd through 4th indexed elements in the list values. Note that the second index is not inclusive.

You can then calculate the percent increase or decrease, by taking the difference of the two 7-day averages and dividing by last week’s average.

  • Hint
    • Note that you can detect division by zero by handling a ZeroDivisionError with a try and except block. For example:
    try:
    numerator / denominator
except ZeroDivisionError:
    ...

    Take a look at Week 3 in CS50P for more on exceptions in Python.

Thought Question

Why do you think some websites, such as The Washington Post post different values than your program generates for “Average daily new cases” and “Change in avg. daily cases in last 7 days” for some states, and the same values for others?

How to Test Your Code

Your program should behave per the examples below.

seven-day-average/ $ python seven-day-average.py
Choose one or more states to view average COVID cases.
Press enter when done.

State: Massachusetts
State: New York
State: 

Seven-Day Averages
Massachusetts had a 7-day average of 1646 and an increase of 46%.
New York had a 7-day average of 7502 and a decrease of 1%.

seven-day-average/ $ python seven-day-average.py
Choose one or more states to view average COVID cases.
Press enter when done.

State: Maine
State: California
State: 

Seven-Day Averages
California had a 7-day average of 20461 and a decrease of 8%.
Maine had a 7-day average of 196 and a decrease of 10%.

Do note that the numbers will vary each day, since the data you are using is updated daily.

No check50 for this one!

To evaluate that the style of your code, type in the following at the $ prompt.

style50 seven-day-average.py

How to Submit

No need to submit! This is a practice problem.