Exercise: Treating People as Objects

Introduction

In this exercise you will practice defining and using classes, and performing simple manipulations of collections of objects.

Problem Description

You need to view some data about people in various ways.

Solution Description

The people.py module has starter code that creates Person objects in a list peeps. In the people.py file:

• Write a Person class with:

  • an __init__ method that takes:
    • a name (str),
    • a birthdate (str) formatted in ISO 8601 format,
    • a height in cm (int),
    • a weight in kilograms (float),
  • a __repr__ method that returns a str like <name, birthdate, height, weight> field, e.g., <Stan, 2008-08-13, 150cm, 45kg>;
  • a height_inches method that returns the Person object’s height in inches (1in = 2.54cm), and
  • a weight_pounds method that returns the Person object’s weight in pounds (1kg = 2.2lb).
  • a days_unitl method that takes an age in years and returns the number of days until (or since, as a negative number) this Person turns age years old.

Do the following exercises to practice using Person objects:

• Write an expression that assigns to avg_height the average height of the Person objects in peeps.

• Write an expression that assigns to avg_weight the average weight of the Person objects in peeps.

  • Bonus: write a function, avg_by, that takes a sequence of Person objects and a key function specifying the attribute of Person objects to take the average of, similar to the key function of sorted.

• Write an expression that assigns to name2height a Dict[str, int] that maps Person names to their heights.

• Write an expression that assigns to name2weight a Dict[str, int] that maps Person names to their weights.

  • Bonus: write a function, dict_builder, that takes a list of ojects and a key_val function that takes a single parameter that is an element of the list, and returns a tuple that becomes a key-value mapping in a dict returned by dict_builder.

• Write an expression that assigns to peeps_by_age a list of Person objects in peeps sorted in descending order by age.

• Write a loop that prints the names and ages until they turn 18 of all the Persons in peeps.

Sample Answer

Don’t peek until you’ve tried it yourself!

• people_answers.py