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Lab 2: Defining Functions and Testing Them

This repository includes existing code that will test your understanding of Python arithmetic and algebra as well as help you define your own functions. Start by forking it to your own account and then cloning your fork in PyCharm. Lab 1 includes instructions on how to do this, so you should refer there if you do not remember how. (You can also clone this repo without forking, but you won't be able to push any changes you might make.)

Once you have opened the cloned Git repo in PyCharm, you may have to edit a Python source file and wait a few seconds for PyCharm to configure your Python environment. When it's settled down, you'll be ready to move on. If you need help at any time, please ask your Peer Mentors John Nguyen and Yingliao Wang.

Please review the following concepts from lecture 2 before starting this lab:

  • Numbers, strings, booleans, and operations on those
  • Tuples
  • Defining and using your own functions

A quick review of boolean algebra

  • Boolean values are not strings!
    • They are surrounded by quotes
  • True and False are the only values in the bool type
  • Boolean expressions are expressions that evaluate to True or False
x == y               # x is equal to y
x != y               # x is not equal to y
x > y                # x is greater than y
x < y                # x is less than y
x >= y               # x is greater than or equal to y
x <= y               # x is less than or equal to y
  • operators such as and or or are evaluated left-to-right
not x	        # Returns True if x is True, False otherwise
x and y	        # Returns x if x is False, y otherwise
x or y	        # Returns y if x is False, x otherwise

A quick review or arithmetic operations

  • Addition: 8 + 5
  • Subtraction: 8 - 5
  • Multiplication 8 * 5
  • Division: 8 / 5
  • Floor Division: 8 // 5
  • Exponent: 8 ** 5
  • Modulus: 8 % 5

A quick review of tuples

Named tuples allow us to define data classes with type hinting. To create a named tuple, use the following syntax:

from typing import NamedTuple  # >= Python.3.6.0

class Employee(NamedTuple):
  name: str
  department: str
  salary: int
  is_remote: bool = False  # >= Python.3.6.1
    
bob = Employee(name='Bob', department='IT', salary=10000, is_remote=True)

Defining your functions

  1. First open lab2
  2. Notice how the function full_name is defined
    • Can you explain what is happening to the given Strings
  3. Fill in the code to define the function is_even
    • What operators do you need?
  4. Define the Position NamedTuple to represent the coordinates of a sphere
  5. Now define the volume of a sphere
    • Does order of operations matter?
    • What arithmetic operations do you need?
  6. Now look at the overlap function
    • What exactly is it asking you to define? Look at this WolframMathWorld for some hints
    • To speed up your calculation, how would you account for the case in which r=R?
      • How would you implement this? 7 Take some time to attempt to implement the other functions such as contained_within and trilateration
    • Hint: Notice that the parameters and return type for trilateration are empty
      • What would you fill in for the parameters and return given the description of what the function does in the comments. This one may be hard, so try to figure out what inputs and outputs the function would take. You don't have to attempt to implement it
      • Hint: you can google 'True range multilateration' or 'trilateration'
    • What is intersect returning?
      • How do we input two circles and receive the correct output?

Testing your functions

After you have written a few functions and are ready to move on, we will be writing basic assertion tests.

Assertions are statements that assert or verify computations in your program. They are boolean expressions that evaluate to true or not.

If the assertion is true, the program does nothing; however, if the assertion is false, the program stops and throws an error.

Because assertions can stop a program and print a message, they may be useful to showing where program errors have occured.

Python has a built-in assert statement:

assert <condition>
assert <condition>, <error message>

If the assert evaluates the false the Python program halts and gives us an AssertionError

  1. Reference the short tests already written in test_lab2,
  2. write some short assertion tests to verify that you program works.
  3. Run the following command in the lab2 directory to run your tests.
$ pipenv run pytest

If you encounter any errors you may have the wrong version of Python

Let us know if you have any questions. Once you've successfully written some tests you are free to leave.