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Homework 7: For Loops

Objectives

The goal of this assignment is to gain experience working with for loops:

  • Iterating elements of a list
  • Iterating characters of a string
  • Iterating over a range of indexes

Notices

Stubs Provided

To save you time on this assignment, we are giving you starter files with all the docstrings already written. Download and unzip HW7-stubs.zip. Don't forget to write your name at the top of each file!

Don't Use while

This homework is about for loops. Be sure not to use while loops (which was last week's topic) in any of the exercises.

Submissions Limited

For HW7, you may submit each exercise up to 20 times. Before you submit to Gradescope, make sure that you:

  1. Test your code, either in the shell or in the __main__ block.
  2. Run !ruff check, and resolve all issues.

Executable Documentation

💡 Python's doctest module provides features that facilitate testing code. If function docstrings in your program include example function calls, doctest will notice them, and if you ask it to (see the stubs for the following homework problems), doctest will run your functions with the documented example arguments and alert you if the result doesn't match the docstring.

To try it out, open any of the downloaded "stubs" in Thonny and click Run.

Exercise 7.1 Concept Questions

Complete the "HW 7.1" assignment on Runestone.

Exercise 7.2 Intervals

For this exercise, write a function that takes a list of floats and returns a new list containing only the numbers that are within a designated interval. The file must be named interval.py and it must contain a function named in_interval with four parameters:

  • The original list of float numbers.
  • The lower bound of the interval.
  • The upper bound of the interval.
  • Boolean indicating whether this is a closed interval. This parameter should have a default value of True, indicating that an interval is closed by default.

The numbers in the returned list must be in the same order as they appeared in the original list. You may assume that the provided lower and upper values represent a valid interval.

Here are some examples illustrating the expected behavior:

>>> in_interval([20.1, 0.0, 2.5, 1.4, -6.0], 0.0, 5.0)  # Default is closed
[0.0, 2.5, 1.4]
>>> in_interval([20.1, 0.0, 2.5, 1.4, -6.0], 0.0, 5.0, False)
[2.5, 1.4]

Exercise 7.3 Shift Cipher

One of the simplest forms of encryption is the Caesar Cipher, also known as a shift cipher. In this technique, each letter in the plaintext is replaced by a letter a fixed distance away in the alphabet, wrapping around at the end (or beginning) as necessary.

image Shift cipher example

For example, if you encoded 'dog' by shifting two to the right, 'd' would be replaced by 'f', 'o' would be replaced by 'q', and 'g' would be replaced by 'i', so the final encoded text would be 'fqi'. 'zoo' would be encoded as 'bqq', because the 'z' would wrap around to the beginning of the alphabet again.

Create program called shift_cipher.py containing the function encode. The function should take as parameters the text to encode (in all lower case), and the number of letters to shift (guaranteed to be between -26 and 26). It should return the encoded text, and leave spaces and punctuation as-is, without changing them.

>>> print(encode("the quick brown fox.", 4))
xli uymgo fvsar jsb.

Hint

You will need to use ord() and chr() to convert letters to numbers and back again in order to shift them. You should also use the remainder operator (%), although a less optimal solution is possible using if statements.

Exercise 7.4 Parking Lot

There's a major event happening at the fairgrounds, and cars are lining up from everywhere. We need a program to help vehicles find a parking spot when they arrive. Since parking is limited, and not all of the spots are the same size, we need to be careful to put smaller vehicles in the smaller spots so that we can save the larger spots for vehicles that need them.

For the sake of simplicity both cars and parking spots will be represented as a tuple which contains the width of the car/spot followed by the length of the car/spot. Define a function named best_fit in parking.py with the following arguments:

  • a tuple representing the car that is trying to park
  • a list of tuples representing the available parking spots

In order to fit in a parking spot, there must be at least 2 feet of space around all sides of the car when parked. This will allow people to safely enter and exit their cars, walk around the vehicles and load and unload items. The image below shows a car with tuple (6, 10) that exactly fits in a parking spot with tuple (10, 14), due to the 2 feet of space in all directions.

image

The function should return the position in the list of the parking spot which best fits this car, i.e. the spot with the least amount of total excess space around the car. In the case of ties, the spot with the larger index should be selected. If there is no spot that can accommodate the car, then the function must return None.

Here are some examples: 

>>> print(best_fit((3, 4), [(5, 5), (10, 12), (7, 8), (7, 9), (8, 8)]))
2
>>> print(best_fit((3, 4), [(5, 5), (10, 12), (3, 4), (7, 9), (8, 8)]))
3
>>> print(best_fit((3, 4), [(5, 5), (10, 12), (3, 4), (7, 9), (7, 9)]))
4
>>> print(best_fit((9, 12), [(5, 5), (10, 12), (3, 4), (7, 9), (7, 9)]))
None

Hint

Here is an outline of the solution:

  1. Initialize the best parking space's index to None (not yet found)
  2. For each parking space in the list:
    • If the current space legally fits the car
      • If the current space's area is less than or equal to the best space's area
        • Replace the best space's index with the current space's index
  3. Return the best parking space's index

HW7 Reflection (required)

Submit the graded survey on Canvas after completing the assignment.