Project 2: Autocorrected Typing Software

Programmers dream of
Abstraction, recursion, and
Typing really fast.


Important submission note: For full credit:

  • Submit Phase 1 by Wednesday, 11/13.
  • Submit the whole project by Sunday, 11/17.

You may work with a partner for the entire project.

In this project, you will write a program that measures typing speed. Additionally, you will implement typing autocorrect, which is a feature that attempts to correct the spelling of a word after a user types it. This project is inspired by Type Racer.

Final Product

A solution to the project can be interacted with at - if you'd like, try it out now! When you finish the project, you'll have implemented a significant part of this game yourself!

Download starter files

You can download all of the project code as a zip archive. This project includes several files, but your changes will be made to only Here are the files included in the archive:

  • The typing test logic.
  • Functions for interacting with files and strings.
  • data/sample_paragraphs.txt: A file containing text samples to be typed.
  • data/words.txt: A file containing English words in order of frequency.
  • A web server for the web-based graphical user interface (GUI).
  • gui: A directory of files needed for the graphical user interface (GUI).
  • Utility functions for CS 61A.
  • images: A directory of images.


The project is worth 20 points. 17 points are assigned for correctness of your final code, 1 point for submitting Phase 1 by the checkpoint deadline, and 2 points for composition.

You will turn in the following files:


You do not need to modify or turn in any other files to complete the project.

For the functions that we ask you to complete, there may be some initial code that we provide. If you would rather not use that code, feel free to delete it and start from scratch. You may also add new function definitions as you see fit.

However, please do not modify any other functions. Doing so may result in your code failing our tests. Also, please do not change any function signatures (names, argument order, or number of arguments).

Throughout this project, you should be testing the correctness of your code. It is good practice to test often, so that it is easy to isolate any problems. However, you should not be testing too often, to allow yourself time to think through problems.

Phase 1: Typing

Problem 1 (1 pt)

Implement choose, which selects which paragraph the user will type. It takes a list of paragraphs (strings), a select function that returns True for paragraphs that can be selected, and a non-negative index k. The choose function return's the kth paragraph for which select returns True. If no such paragraph exists (because k is too large), then choose returns the empty string.

Problem 2 (2 pt)

Implement about, which takes a list of topic words. It returns a function that can be passed to choose as the select argument. The returned function takes a paragraph and returns whether that paragraph contains any of the words in topic.

To make this comparison accurately, you will need to ignore case (that is, assume that uppercase and lowercase letters don't change what word it is) and punctuation.

Assume that all words in the topic list are already lowercased and do not contain punctuation.

Hint: You may use the string utiltiy functions in

Problem 3 (1 pt)

Implement accuracy, which takes a typed paragraph and a reference paragraph. It returns the percentage of words in typed that exactly match the corresponding words in reference. Case and punctuation must match as well.

A word in this context is any sequence of characters separated from other words by whitespace, so treat "dog;" as all one word.

If a typed word has no corresponding word in the reference because typed is longer than reference, then the extra words in typed are all incorrect.

If typed is empty, then the accuracy is zero.

Problem 4 (1 pt)

Implement wpm, which computes the words per minute, a measure of typing speed, given a string typed and the amount of elapsed time in seconds. Despite its name, words per minute is not based on the number of words typed, but instead the number of characters, so that a typing test is not biased by the length of words. The formula for words per minute is the ratio of the number of characters typed divided by 5 (a typical word length) to the elapsed time in minutes.

For example, the string "I am glad!" contains three words and ten characters (not including the quotation marks). The words per minute calculation uses 2 as the number of words typed (because 10 / 5 = 2). If someone typed this string in 30 seconds (half a minute), their speed would be 4 words per minute.

Time to test your typing speed! You can use the command line to test your typing speed on paragraphs about a particular topic. For example, the command below will load paragraphs about cats or kittens. See the run_typing_test function for the implementation if you're curious (but it is defined for you).

python3 -t cats kittens

You can try out the web-based graphical user interface (GUI) using the following command. This interface picks random paragraphs instead of choosing by topic.


Phase 2: Autocorrect

In the web-based GUI, there is an autocorrect button, but right now it doesn't do anything. Let's implement automatic correction of typos. Whenever the user presses the space bar, if the last word they typed doesn't match a word in the dictionary but is close to one, then that similar word will be substituted for what they typed.

Problem 5 (2 pt)

Implement autocorrect, which takes a user_word, a list of all valid_words, a diff_function, and a limit.

If the user_word is contained inside the valid_words list, autocorrect returns that word. Otherwise, autocorrect returns the word from valid_words that has the lowest difference from the provided user_word based on the diff_function. However, if the difference is greater than limit, then user_word is returned instead.

A diff function takes in three arguments, which are the two strings to be compared (first the user_word and then a word from valid_words), as well as the limit. The output of the diff function, which is a number, represents the amount of difference between the two strings.

Assume that user_word and all elements of valid_words are lowercase and have no punctuation.

Important: if multiple strings have the same lowest difference according to the diff_function, autocorrect should return the string that appears first in valid_words.

Hint: Try using max or min with the optional key argument.

Problem 6 (2 pts)

Implement swap_diff, which is a diff function that takes two strings. It returns the minimum number of characters that must be changed in the start word in order to transform it into the goal word. If the strings are not of equal length, the difference in lengths is added to the total.

Here are some examples:

>>> big_limit = 10
>>> swap_diff("nice", "rice", big_limit)    # Substitute: n -> r
>>> swap_diff("range", "rungs", big_limit)  # Substitute: a -> u, e -> s
>>> swap_diff("pill", "pillage", big_limit) # Don't substitute anything, length difference of 3.
>>> swap_diff("roses", "arose", big_limit)  # Substitute: r -> a, o -> r, s -> o, e -> s, s -> e

If the number of characters that must change is greater than limit, then swap_diff should return any number larger than limit and should minimize the amount of computation needed to do so.

These two calls to swap_diff should take about the same amount of time to evaluate:

>>> limit = 4
>>> swap_diff("roses", "arose", limit) > limit
>>> swap_diff("rosesabcdefghijklm", "arosenopqrstuvwxyz", limit) > limit

Important: You may not use while or for statements in your implementation. Use recursion.

Try turning on autocorrect in the GUI. Does it help you type faster? Are the corrections accurate? You should notice that inserting a letter or leaving one out near the beginning of a word is not handled well by this diff function. Let's fix that!

Problem 7 (3 pt)

Implement edit_diff, which is a diff function that returns the minimum number of edit operations needed to transform the start word into the goal word.

There are three kinds of edit operations:

  1. Add a letter to start,
  2. Remove a letter from start,
  3. Substitute a letter in start for another.

Each edit operation contributes 1 to the difference between two words.

>>> big_limit = 10
>>> edit_diff("roses", "arose", big_limit)     # roses -> aroses -> arose
>>> edit_diff("tesng", "testing", big_limit)   # tesng -> testng -> testing
>>> edit_diff("rlogcul", "logical", big_limit) # rlogcul -> logcul -> logicul -> logical

We have provided a template of an implementation in This is a recursive function with three recursive calls. One of these recursive calls will be similar to the recursive call in swap_diff.

You may modify the template however you want or delete it entirely.

If the number of edits required is greater than limit, then edit_diff should return any number larger than limit and should minimize the amount of computation needed to do so.

These two calls to edit_diff should take about the same amount of time to evaluate:

>>> limit = 2
>>> edit_diff("rlogcul", "logical", limit) > limit
>>> swap_diff("rlogculabcdefghijklm", "logicalnopqrstuvwxyz", limit) > limit

Try typing again. Are the corrections more accurate?


Extensions: You may optionally design your own diff function called final_diff. Here are some ideas for making even more accurate corrections:

  • Take into account which additions and deletions are more likely than others. For example, it's much more likely that you'll accidentally leave out a letter if it appears twice in a row.
  • Try to incorporate common misspellings

Phase 3: Multiplayer

Typing is more fun with friends! You'll now implement multiplayer functionality, so that when you run on your computer, it connects to the course server at and looks for someone else to race against.

To race against a friend, 5 different programs will be running:

  • Your GUI, which is a program that handles all the text coloring and display in your web browser.
  • Your, which is a web server that communicates with your GUI.
  • Your opponent's
  • Your opponent's GUI.
  • The CS 61A multiplayer server, which matches players together and passes messages around.

When you type, your GUI sends what you have typed to your server, which computes how much progress you have made and returns a progress update. It also sends a progress update to the multiplayer server, so that your opponent's GUI can display it.

Meanwhile, your GUI display is always trying to keep current by asking for progress updates from, which in turn requests that info from the multiplayer server.

Each player has an id number that is used by the server to track typing progress.

Problem 8 (2 pt)

Implement report_progress, which is called every time the user finishes typing a word. It takes a list of the words typed, a list of the words in the prompt, the user id, and a send function that is used to send a progress report to the multiplayer server.

Your progress is a ratio of the words in the prompt that you have typed correctly, up to the first incorrect word, divided by the number of prompt words. For example, this example has a progress of 0.25:

report_progress(["Hello", "ths", "is"], ["Hello", "this", "is", "wrong"], ...)

Your report_progress function should return this number. Before that, it should end a message to the multiplayer server that is a two-element dictionary containing the keys 'id' and 'progress'. The id is passed into report_progress from the GUI. The progress is the fraction you compute. Call send on this dictionary to send it to the multiplayer server.

Problem 9 (3 pt)

Implement fastest_words, which returns which words each player typed fastest. This function is called once both players have finished typing. It takes word_times and a positive margin.

The word_times argument is a list of lists of word_time values, one list for each player, and within each list n+1 elements for the total elapsed time in the race after that player has finished typing each of the n words, as well as an entry at the beginning with zero elapsed time for the special word 'START'.

It returns a list of lists of words, one list for each player, and within each list the words they typed the fastest.

Definition: A player typed a word the fastest if the difference between their elapsed time for that word and the previous word is within margin of the smallest difference for any player. Therefore, if two players type a word within margin of each other, that word will appear in both of their lists.

Be sure to use the word and elapsed_time accessor functions for the word_time data abstraction, rather than assuming a particular data format.

Congratulations! Now you can play against other students in the course. Set enable_multiplayer to True near the bottom of and type swiftly!