CS257 Software Design
Friday, 9 May 2025


def clean_text(s):
    s = s.replace("'", "''")
    s = s.replace(...)
    ...

@app.route('/whatever')
search_text = clean_text(flask.request.args('search_text'))
s

query = ''' SELECT title, surname
FROM books, authors, books_authors
WHERE books.id = books_authors.book_id
AND authors.id = books_authors.author_id'''

params = []
if there's a "search_text" GET parameter:
    query = query + " AND author.surname LIKE '...%s...'"
    params.append(search_text)

cursor.execute(query, params)
...
print(cursor.query)


+ Questions?

+ Readings
- writing good functions
    - in the *calling code* a function invocation
        should make sense
    - every function should do one thing
        "functional cohesion"

        # 2 things in one function: BAD
        def is_prime(n):
            ...do some stuff...
            if it_is_prime: # assumes that what the caller wants
                print(n)    # is to print primes
            return it_is_prime

    - keep it brief (but not too brief)

        # good
        def is_prime(n):
            ... (<= 150 lines)
            return result

        # bad
        def add_one(n):
            return n + 1

    - "does the routine's parameter list, taken as a whole
        present a consistent interface abstraction?"

      Jeff's version: "does the name of the function tell me
        roughly what the function does, and does this list of
        parameters make sense as 'the info the function needs
        to do its job'"

        Here, the info the function needs to do its job
        consists of the integer in question. That's the parameter.
        The info the caller needs back (via the return value)
        is "yes or no, it's prime".

        def is_prime(n):
            ''' Returns True if the integer n is a prime
                integer, and False otherwise '''

        # Ugh. This fails on many levels.
        def do_something(operation, param1, param2, param3):
            ''' if operation = 0, do a Caesar cipher encryption
                    of string param1 using shift param2, and ignore param3
                if operation = 1, do some other damn thing
                    ...
            '''

- writing (or not) good comments
    - Section headers in a long function are good
    - Don't just repeat the code; give a higher-level description
        of what's going on. (Mostly, I use this kind of comment
        to document functions.)
    - Both of the above, clarifying relationship between
        info coming in and info going out is important
    - Top-of-file "what does this file do?" + copyright/authorship
    - Bad: comment repeats what the code says
        x = x + 1  # increment x
    - If the code is clear enough at a glance, don't comment it
    - Comments can go out of date; this is very bad
    - If you need heavy summarizing comments, maybe the code itself is bad

+ Web pages: what happens when?
- clients, servers, sequence of events
- curl
- browser developer tools
- impact of multi-processing
- what's it all mean for
    - desktop vs phone
    - speed of loading
    - what's going on on scam or ad-heavy sites?

+ Happy Friday!