HW6 - Spell Checker#

Learning objective: Implement efficient code with generators.

Rubric & Submission#

Please note these important things:

  • You will NOT turn this into AutoGrader. You will Submit to Replit.

  • This will be for your High School Grade only. It will be worth 40 points (40% a UW Homework Assignment).

  • You will be graded on the Replit Unit Tests only. ~3pts per Unit Test.

  • You will not be graded on any commenting or tests you write.

  • Please know the due date and TIME as posted in Schoology. (6am Feb 3)


In this project you will learn:

  • Class implementation (should just be extra practice by now)

  • The importance of efficiency

  • How to do implement spelling suggestions

  • How to do implement a generator

All of these things will accomplished by implementing a SpellChecker class.

Your Spell Checker program will be giving a list of words to use as its dictionary. The primary pieces of functionality will be to:

  • Determine if a single word is misspelled

  • Find all the misspelled words in an essay (text file)

  • Provide a set of correctly spelled words as suggested corrections

A basic infrastructure of the SpellChecker class will be provided.

Spell Checking an Essay#

First, improve the code so that it can complete the spell checking quickly.

You will implement the following three things in the class SpellChecker:

  1. constructor : Takes the name of a dictionary and intializes a SpellChecker object.

  2. misspelled : An instance method that returns True if the word passed in is not found in the dictionary.

  3. spell_check : An instance method that returns a list of misspelled words found in the essay while also outputting to the console details about which words are misspelled.

There are several Unit Tests that related to the above that you should pass before continuing onto the next step. Note that these Unit Test will test both the functionality as well as the speed of execution. You need to have FAST code!!

Also, the output printed to the console for spell_check should look close to:

civalized: line: 1  word:3
oportunities: line: 6  word:4
seeems: line: 15  word:9
peopl: line: 21  word:8
ettiquitt: line: 35  word:1
shoudl: line: 37  word:7
psudo-code: line: 37  word:10
algorythm: line: 39  word:6

Be sure you Pass the Unit Tests:

  • test_misspelled

  • test_check_essay

  • test_check_essay_speed_not_garbage

  • test_check_essay_speed_okay

  • test_check_essay_speed_good

Tips for Passing Test#

Make sure that you have your own tests written. You will understand the input and expected output of your own tests. This will assure that things are working according to plan.

Mr. Stride will ask to see your tests first before helping you figure out why a functional Unit Test is failing.

You need to update misspelled to work with hyphenated words. There is a slick and easy recursive approach to this which is also very fast.

Hint: If no hyphen, solve normally. If it has hyphens, break into subwords and solve for each subword.

misspelled needs to work with hyphenated words with multiple hyphens!

Example: word-is-good-now is correctly spelled!

If you are not passing the speed checks, it could be several things:

  • Maybe Mr. Stride’s test are bad. Do other students’ tests pass?

  • Verify that the data structure you’re using to hold the dictionary is fast.


Before we move onto the next phase of development, you need to learn about generators.

In Python, a generator is a special type of function that produces a sequence of values, one at a time, when iterated over. Generators are different from regular functions in that they do not return all their output at once; instead, they yield their values one at a time, which allows them to be more memory-efficient than regular functions that return all their output at once.

Here is a simple example of a generator in Python:

def countdown(n):
    while n > 0:
        yield n
        n -= 1

for i in countdown(5):

This generator, countdown, yields the values 5, 4, 3, 2, and 1, one at a time, when it is iterated over. When the generator is called, it does not execute the code inside of it immediately; instead, it returns a special type of iterator called a “generator iterator”, which can be used to execute the code in the generator one step at a time.

Generators can be very useful for producing large sequences of data, because they allow you to generate the values one at a time, rather than creating a list with all the values at once, which can be very memory-intensive.

Here are a couple of YouTube videos that explain generators in Python:

These videos provide a good overview of generators, including how to create them, how to use them, and some of the benefits of using generators in your Python code.

Spelling Suggestion#

This is where the project starts to get more interesting. There are many creative ways to suggest words for a misspelled word. We will start simple and then build up to AMAZING!


We will start with a concept that I’ll call: mis-misspelled. The basic idea is that we will modify the spelling of a misspelled word until it is modified into a correctly spelled word.

For example: Let’s consider the misspelled word, aple. If we modify aple by introducing another p into the ‘3rd’ position (after the second letter) then we will generate the word apple which is correctly spelled!

Using this concept, we could have the following code:

def get_suggestion(self, misspelled_word):
    for mis_misspelled_word in create_misspelling(misspelled_word):
        if not misspelled(mis_misspelled_word):
            return mis_misspelled_word

For each section below, attempt find the correct spelling for words using the generator just created.

Part 1#

You will implement a create_misspelling generator, but instead of using the name ‘create_misspelling’, we will use a more specific name that describes exactly how we are misspelling the word. Let’s name it: _insert_letters.

Note: we prefix the name with _ because it is a private method. Also, this method is an instance method (belongs to the object).

This method will insert all the letters, a-z, into every possible position of a given word.

Be sure you pass the Unit Test:

  • test_insert_letters

Part 2#

Implement another generator to move all letters, one letter at a time. This will be called: _remove_letters. For example:

   for word in self._remove_letters('goodbye'):

# prints

Be sure you pass the Unit Test:

  • test_remove_letters

Part 3#

Implement another generator to change all letters, one letter at a time. This will be called: _swap_letters. Note that this does NOT mean that two letters in the word is swapped. Instead, it means that one letter is swapped out for another. For example:

   for word in self._swap_letters('ab'):

# optionally prints 'ab', but definitely prints...

Be sure you pass the Unit Test:

  • test_swap_letters


It is time to implement the method suggest_correction. This method should return a list of suggested words that could be the correct spelling for the misspelled word. The list will have an maximum number of words added to the list which is specified in the optional max argument.

    def suggest_correction(self, word, max=6):
        # student's implementation goes here


Each generator above catches some types of mistakes, but not all of them. In fact, you can’t even try all three back-to-back-to-back because some misspelled words require ALL THREE at the SAME TIME!! For example, to identify the correctly spelled word etiquette from ettiquitt requires that we delete a t, add an e, and change an i to an e. All three!!

We want to implement all 3 types, composed with one another. This can be difficult. Here is a way to compose all three together:

    def suggest_correction(self, word, max=6):
        # partial implementation only!!
        fns = [self._insert_letters, self._remove_letters, self._swap_letters]
        for word in self._compose_fns(word, fns):
            # rest of code not shown

    def _compose_fns(self, word, fns):
        A recursive generator that composes all the generators in fns.
        word : the word that is misspelled
        fns : a list of generators
        for fn1_word in fns[0](word):
            yield fn1_word
            if len(fns) == 1:
                yield fn1_word
                # our recursive case must be in the form of a for-loop
                for fn2_word in self._compose_fns(fn1_word, fns[1:]):
                    yield fn2_word

Be sure you pass the Unit Test:

  • test_suggest_compose : This tests that suggest_correction correctly finds a suggestion for a misspelled word that requires three changes.

Using the above code, see if you can correctly produce at least one suggestion for each of the misspelled words in englishEssay.txt.

Note: Your code may run for as much as a full minute to find suggestions for all the misspelled words in the englishEssay.txt.

Levenshtein Distance#

There are two problems with what we’ve done so far:

  1. It’s too slow!!

  2. The list may contain lots of odd words

We are going to change the approach to solving this Suggestion Problem. We will essentially go backwards. Instead of generating mis-misspelled candidates and then search the dictionary to see if it is indeed a correctly spelled word, we will compare ‘every’ word in the dictionary against the misspelled word to see if it is ‘close’. The ‘closests’ words will be what we suggest.

To accomplish this, we need a way to measure the ‘distance’ between two words. The Levenshtein Distance algorithm is exactly what we want. The algorithm will provide an integer number that is essentially the count of changes made to one word to reach the other. The changes are exactly the same three generators you implemented above. (The algorithm will not use your generators.)

You will add a new instance method to the SpellChecker class.

    def lev_suggest_correction(self, word):
       Return a list of all the suggest words that share the same, minimum
       distance from word using the levenshtein distance algorithm.

It can take a while to understand the algorithm which can take us off topic quite a bit. So, instead, you have been provided with three different implementations of the algorithm in the file levenshtein.py.

Below are the names of the 3 implementations along with the time (in seconds) it took to provide suggestions for all the misspelled words in the englishEssay.txt. (Times were using Mr. Stride’s implementation. Measured only once.)

  1. levenshtein_distance: 71.16

  2. lev_distance:         51.45

  3. fast_lev_distance:     1.42

It is pretty clear that one implementation is much, much, much faster than the rest. This is because it is implemented in the Python module editdistance written in C++. Because it is written in C++ the code can run a lot faster. Furthermore, some braniacs out there used some fancy math an algorithm techniques to speed it up even more.

Experience the Difference#

Implement the lev_suggest_correction and experience the difference in speed from one algorithm to the other. Amazing, right?!

Be sure you pass the final two Unit Tests:

Challenge Question#

This challenge question is a bit different than previous questions. Here, you’ll be asked to do some Data Science research. The goal is to provide visual insight into a mathematical solution space. Does this sound a bit strange? Let me elaborate.

You will have to:

  • Learn some Math theory – how to generate Pythagorean Triples.

  • Write efficient code to solve a problem quickly – I used generators, but that is not absolutely necessary.

  • Apply some creative analysis to imagine visually appealing & insightful graphs.

  • Create and annotate graphs – For reference, use: Mr. Stride’s IDP Site and/or ChatGPT

  • Interpret the data an draw some conclusions.

ChatGPT & Plagiarism

This challenge question deals mostly with your ability to understand new things, search the internet, write code that solves your problem, and, MOST IMPORTANTLY create visually insightful graphs.

You could turn this into an exercise to learn how much ChatGPT can do for you from the get-go. Or, you could use ChatGPT to help when you get stuck with creating specific graphs. It is up to you. It is a resource.

Keep the end goal in mind: LEARN how to provide visual INSIGHT.

There is NO possibility of being accused of plagiarism on this Challenge Question. It isn’t graded!!

Pythagorean Triples#

Before you can really begin to solve this problem, you need to learn about how to generate Pythagorean Triples. You can get a great lesson by watching this video by 3 Blue 1 Brown. You definitely should watch it!!

Coding Hints#

You’ll want to start by creating a method that generates all the fractions up to some maximum denominator. For example, here are all the fractions up through the denominator 9: \(\frac{1}{2}, \frac{1}{3}, \frac{2}{3}, \frac{1}{4}, \frac{3}{4}, \frac{1}{5}, \frac{2}{5}, \frac{3}{5}, \frac{4}{5}, \frac{1}{6}, \frac{5}{6}, \frac{1}{7}, \frac{2}{7}, \frac{3}{7}, \frac{4}{7}, \frac{5}{7}, \frac{6}{7}, \frac{1}{8}, \frac{3}{8}, \frac{5}{8}, \frac{7}{8}, \frac{1}{9}, \frac{2}{9}, \frac{4}{9}, \frac{5}{9}, \frac{7}{9}, \frac{8}{9}\)

I created a generator in Python so that I could write the following:

for a, b in gen_fractions(9):
    print(a, '/', b)

Once you have the ability to generate all the fractions you need, use each fraction to generate all the Pythagorean Triples with a hypotenuse <= max_length using a specific complex number (u + vi) where u and v come from the fraction. Put this into a nested loop and, voila, you have all the Triples! I personally had some repeats that needed to be removed using an “appropriate” data structure.

The goal would be to create a function that counts the total number of Triples that have an hypotenuse <= max_length. If done correctly, you should find that count_triples(2125) == 2131. In other words, there are 2131 unique Pythagorean Triples that have an hypotenuse <= 2125. Calculating this should be very quick!

For efficiency, you’ll want to save the data in appropriate data structures as you generate the data. If you regenerate data for all lengths, you’ll be dog slow! For example, please do NOT do the following:

counts = []
for c in range(max_hypotenuse):

The avoid the above code, you may have to refactor or reorganize your code in ways that allow you to save data as you go.

To help you validate your code, ere is a table of the count of Triples for a specific Max Hypotenuse:

Count   Max Hypotenuse
  1      5
  2      10
  3      13
  4      15
  5      17
  6      20
  8      25
  9      26
 10      29
 11      30
 12      34
 13      35
 14      37
 15      39

The above table says that there are 13 unique Triples whose hypotenuse is of length 35 or less.

If you struggle with creating the code to generate these values, use online resources to help. There is sooooo much more to this problem than coding a quick solution. BUT you should at least understand the code you’ve acquired, and don’t forget to annotate where you got the code.

Graphs with Insight#

The obvious graph is something like this:
Basic Plot

There are lots of graphs you can generate to show the distribution of Triples, the growth rate, the cost to generate the count, the discovery rate of Unique Triples from each fraction, the line or parabola of best fit, how many unique Triples are found for an hypotenuse, and more!

Here are two more sample graphs that you can attempt to recreate or improve upon: Parabola Fit
Note that the above histogram says that after generating all Triples where the hypotenuse <= 6000, there was one hypotenuse length (5525) that had 22 unique Triples, all of which had a hypotenuse of length 5525.

Draw some Conclusions#

What can you say about the count and distribution of Triples?
Can you accurately predict the count with a line or parabola?
Is it common to find 6 unique Triples for a singular hypotenuse? When does that first happen? What is the distribution?