Reading 07: Functional Programming

Everyone:

Next week, we will explore a new programming paradigm called functional programming, which, if you look closely, is similar to the Unix Philosophy:

By decomposing data processing problems into small functions that work together to process data without side-effects, we can expose opportunities for concurrency and parallelism to build powerful abstractions such as MapReduce.

TL;DR¶

The focus of this reading is to introduce you to functional programming in Python.

Readings¶

The readings for this week are:

Real Python

Optional Resources¶

Here are some additional resources:

Quiz¶

This week the reading is split into two sections: the first part is a short dredd quiz, while the second part involves a Python script: odds.py.

Preparation¶

To test this script, you will need to download the Makefile and test scripts:

$ git switch master                   # Make sure we are in master branch
$ git pull --rebase                   # Make sure we are up-to-date with GitHub

$ git checkout -b reading07           # Create reading07 branch and check it out

$ cd reading07                        # Go into reading07 folder

# Download Makefile
$ curl -LO https://www3.nd.edu/~pbui/teaching/cse.20289.sp24/static/txt/reading07/Makefile

# Download Skeleton Code
$ curl -LO https://www3.nd.edu/~pbui/teaching/cse.20289.sp24/static/txt/reading07/odds.py

Questions (1 Point)¶

Record the answers to the following Reading 07 Quiz questions in your reading07 branch:

As with Reading 01, you will need to store your answers in a reading07/answers.json file. You can use the form above to generate the contents of this file, or you can write the JSON by hand.

To test your quiz, you can use the check.py script:

$ ../.scripts/check.py
Checking reading07 quiz ...
      Q1 1.00
   Score 1.00 / 1.00
  Status Success

Script: `odds.py` (3 Points)¶

The odds.py script has four implementations of an odds function that processes a stream of input and returns a sequence of only the odd numbers. The first implementation, called odds, is provided to you:

def odds(stream=sys.stdin) -> list[int]:
    results = []
    for line in stream:
        number = int(line)
        if number % 2:
            results.append(number)
    return results

Your task is to implement the three other versions of the same odds function:

odds_fp(stream=sys.stdin) -> Iterator[int]

This function uses map, filter, and a lambda expression to produce a sequence of only the odd numbers from stream.
odds_lc(stream=sys.stdin) -> list[int]

This function uses a list comprehension to produce a sequence of only the odd numbers from stream.
odds_gr(stream=sys.stdin) -> Iterator[int]

This function uses yield to generate a sequence of only the odd numbers from stream.

Testing¶

As you implement odds.py, you can use the provided doctests to verify the correctness of your code:

# Run doctests
$ python3 -m doctest odds.py -v
2 items had no tests:
    odds
    odds.main
4 items passed all tests:
   1 tests in odds.odds
   1 tests in odds.odds_fp
   1 tests in odds.odds_gr
   1 tests in odds.odds_lc
4 tests in 6 items.
4 passed and 0 failed.
Test passed.

You can also use make to run both the doctests and the unit tests:

# Run unit tests (and doctests)
$ make test
Testing Odds ...
test_00_doctest (__main__.OddsTest) ... ok
test_01_mypy (__main__.OddsTest) ... ok
test_02_odds_fp (__main__.OddsTest) ... ok
test_03_odds_lc (__main__.OddsTest) ... ok
test_04_odds_gr (__main__.OddsTest) ... ok
test_05_main_fp (__main__.OddsTest) ... ok
test_06_main_lc (__main__.OddsTest) ... ok
test_07_main_gr (__main__.OddsTest) ... ok

   Score 3.00 / 3.00
  Status Success

----------------------------------------------------------------------
Ran 8 tests in 3.407s

OK

To just run the unit tests, you can do the following:

# Run unit tests
$ ./odds.test -v
...

Submission¶

To submit you work, follow the same process outlined in Reading 01:

#--------------------------------------------------
# Make sure you have already completed Preparation
#--------------------------------------------------
...
$ git add answers.json                # Mark changes for commit
$ git commit -m "Reading 07: Quiz"    # Record changes
...
$ git add Makefile                    # Mark changes for commit
$ git add odds.py                     # Mark changes for commit
$ git commit -m "Reading 07: Scripts" # Record changes
...
$ git push -u origin reading07        # Push branch to GitHub

Pull Request¶

Remember to create a Pull Request and assign the appropriate TA from the Reading 07 TA List.

DO NOT MERGE your own Pull Request. The TAs use open Pull Requests to keep track of which assignments to grade. Closing them yourself will cause a delay in grading and confuse the TAs.