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Best style for Python programs: what do you suggest?

Answer 1

+3 A:

In my opinion, the whole program is questionable. The choices of how things are divided into functions is kind of dopey, and it's documented like a class project, not like real system. The documentation kind of obscures the overall mediocre organization. The entire program shows a bias towards verbosity over clarity.

The construct '''\ is frequently seen. The point of the triple quote construct is that carriage returns and newlines work just fine. There is no need to \ escape the newline.

I will tackle functions I see specific problems in as examples:

Whether or not get_message should exist in that form is debatable. The entire function can be replaced by one line.

def get_message():
    "Gets and returns text entered by the user (until EOF)."
    return sys.stdin.read()

The way main, run_interface_loop, get_character and FUNC interact is confusing and not the best way to handle the problem. In particular, catching SystemExit isn't really a great way to signal your program's end in this case.

def main():
    encode_map, decode_map = load_key(KEY_FILE)
    run_interface_loop(encode_map, decode_map)
    save_key(KEY_FILE, encode_map)

def run_interface_loop():
    exit_picked = False
    while not exit_picked:
        print '''
MENU
====
(1) Encode
(2) Decode
(3) Custom
(4) Finish'''
        choice = sys.stdin.readline()
        if choice == '':
            break  # EOF was reached, no more asking the user for stuff
        choice = choice.strip()
        if choice == '1':
            encode(encode_map, decode_map) # This reads until EOF
            exit_picked = True # and so we might as well exit
        elif choice == '2':
            decode(encode_map, decode_map)
            exit_picked = True # Same here
        elif choice == '3':
            encode_map, decode_map = custom()
        elif choice == '4':
             exit_picked = True
        else:
             print "%s isn't a valid choice, try again." % (choice,)

Omnifarious 2010-06-12 14:40:22

'''\ is perfectly valid. It suppresses an initial newline in the string, but lets all lines line up at the left edge.

Mark Tolonen 2010-06-12 15:27:27

Answer 2

+6 A:

don't use bare excepts;

try:
    with open(filename) as file:
        plain, cypher = file.read().split('\n')
        return plain, cypher
**except:**
    with open(filename, 'w') as file:
        file.write(BACKUP)

it is almost always wrong to use bare excepts, and in this case, it is wrong. Catch the exceptions that you want to catch only, in this case most likely is IOException and the error you might get if the file does not contain a '\n' and your tuple unpacking fails (hint: catch them in separate except clause). Also, you might be interested to check what happens if the user doesn't has write permission to filename.

Is there any reason why you're not using print and raw_input() here?

def get_character(prompt, choices):
    "Gets a valid menu option and returns it."
    while True:
        sys.stdout.write(prompt)
        sys.stdout.flush()
        line = sys.stdin.readline()[:-1]
        if not line:
            sys.exit()
        if line in choices:
            return line
        print(repr(line), 'is not a valid choice.')

you might want to use str.translate() for this:

    sys.stdout.write(encode_map[char] if char in encode_map else char)

Lie Ryan 2010-06-12 14:43:44

If anything, print() and input() would have been used from Python 3. However if memory serves correctly, print() was not flushing correctly; and input() could have raised an exception. Exception handling was mostly avoided in the program since my friend is still new to programming and does not know very much yet. The idea behind the exception loop is that if it fails for any reason, the file will be replaced with something valid that will succeed. If an error was raised for some other reason, the second part of the try/except clause will probably fail for the same reason and crash the program.

Noctis Skytower 2010-06-12 19:05:30

@Noctis Skytower: Re handling SystemExit, then handle it with a finally clause. Say what you mean. There are other exceptions besides SystemExit. The file save is currently skipped for any exception besides SystemExit.

Omnifarious 2010-06-13 15:41:41

Answer 3

+7 A:

Since you asked about formatting and style, I'm surprised that nobody else has mentioned PEP 8 yet. It's nominally a guide for modules that want to be included in the standard library, but I find most of its guidance to be applicable pretty much everywhere.

Forest 2010-06-12 18:24:12

+1. Also this example is two things. A module of functions that do encoding and decoding and a Character mode User Interface (CLI). Please learn about Python modules and break this into two pieces.

S.Lott 2010-06-12 20:56:52

Answer 4

A:

Never call sys.exit() or raise SystemExit inside a function. Instead, raise an exception.

Longpoke 2010-06-12 19:36:37

Answer 5

+1 A:

Also look here for Google's Python coding guidelines. They're mostly in line with the PEP mentioned above but are a bit more restrictive in some areas.

Google Python Style Guide

Khorkrak 2010-06-13 01:58:24

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