My first python program: can you tell me what I'm doing wrong?

Question

I hope this question is considered appropriate for stackoverflow. If not, I'll remove the question right away.

I've just wrote my very first python program. The idea is that you can issue a command, and it's gets sent to several servers in parallel.

This is just for personal educational purposes. The program works! I really want to get better at python and therefore I'd like to ask the following questions:

1. My style looks messy compared to PHP (what I'm used to). Do you have any suggestions around style improvements.
2. Am I using the correct libraries? Am I using them correctly?
3. Am I using the correct datatypes? Am I using them correctly?

I have a good programming background, but it took me quite a while to develope a decent style for PHP (PEAR-coding standards, knowing what tools to use and when).

The source (one file, 92 lines of code)

http://code.google.com/p/floep/source/browse/trunk/floep

Answer 1

Usually is preferred that what follows after the end of sentence : is in a separate line (also don't add a space before it)

if options.verbose:
  print ""

instead of

if options.verbose : print ""

You don't need to check the len of a list if you are going to iterate over it

if len(threadlist) > 0 : 
  for server in threadlist :
    ...

is redundant, a more 'readable' is (python is smart enough to not iterate over an empty list):

for server in threadlist:
  ...

Also a more 'pythonistic' is to use list's comprehensions (but certainly is a debatable opinion)

server = []
for i in grouplist : servers+=getServers(i)

can be shortened to

server = [getServers(i) for i in grouplist]

Answer 2

Before unloading any criticism, first let me say congratulations on getting your first Python program working. Moving from one language to another can be a chore, constantly fumbling around with syntax issues and hunting through unfamiliar libraries.

The most quoted style guideline is PEP-8, but that's only a guide, and at least some part of it is ignored...no, I mean deemed not applicable to some specific situation with all due respect to the guideline authors and contributors :-).

I can't compare it to PHP, but compared to other Python applications it is pretty clear that you are following style conventions from other languages. I didn't always agree with many things that other developers said you must do, but over time I recognized why using conventions helps communicate what the application is doing and will help other developers help you.

---

Raise exceptions, not strings.

raise 'Server or group ' + sectionname + ' not found in ' + configfile

becomes

raise RuntimeError('Server or group ' + sectionname + ' not found in ' + configfile)

---

No space before the ':' at the end of an 'if' or 'for', and don't put multiple statements on the same line, and be consistent about putting spaces around operators. Use variable names for objects and stick with i and j for loop index variables (like our masterful FORTRAN forefathers):

for i in grouplist : servers+=getServers(i)

becomes:

for section in grouplist:
    servers += getServers(section)

---

Containers can be tested for contents without getting their length:

while len(threadlist) > 0 :

becomes

while threadlist:

and

if command.strip() == "" :

becomes

if command.strip():

---

Splitting a tuple is usually not put in parenthesis on the left hand side of a statement, and the command logic is a bit convoluted. If there are no args then the " ".join(...) is going to be an empty string:

(options,args) = parser.parse_args()

if options.verbose : print "floep 0.1" 

command = " ".join(args)

if command.strip() == "" : parser.error('no command given')

becomes

options, args = parser.parse_args()
if options.verbose:
    print "floep 0.1" 

if not args:
    parser.error('no command given')
command = " ".join(args)

---

A python for loop has an unusual 'else' clause which is executed if the loop goes through all of the elements without a 'break':

    for server in threadlist :
        foundOne = False 
        if not server.isAlive() :
            ...snip...
            foundOne = True

        if not foundOne :
            time.sleep(0.010)

becomes

    for server in threadlist:
        if not server.isAlive():
            ...snip...
            break
    else:
        time.sleep(0.010)

---

Getting a list of lines and then joining them back together is a bit long winded:

        result = proc.readlines()
        strresult = ''
        for line in result : strresult+=line 
        self.result = strresult

becomes

        self.result = proc.read()

---

Your library use is good, check out the subprocess module, it's a little more up-to-date.

Your datatypes are fine.

And you'll get lots of other anwsers :-)

Answer 3

String exceptions are deprecated in Python, so this line:

if not config.has_section(sectionname): 
    raise 'Server or group ' + sectionname + ' not found in ' + configfile

should be reworked into something like this:

if not config.has_section(sectionname):
    raise ConfigNotFoundError(
        "Server or group" + sectionname + "not found in" + configfile)

class ConfigNotFoundError(Exception):
    pass

[Edited to reflect the suggestion of dangph in the comments]

It's more lines of code, but it's better for future upgrades.

For readability's sake, something like this:

parser.add_option('-q','--quiet',action="store_false", help="Display only server output", dest="verbose", default=True)

Can be rewritten like this:

parser.add_option('-q',
                  '--quiet',
                  action="store_false",
                  help="Display only server output", 
                  dest="verbose", 
                  default=True)

You might prefer another method of splitting the method call up, but the idea is that long lines can be hard to read.

You should also read PEP 8 to get a sense of Python style.

Answer 4

Often, for reuse purposes, we do the following, starting at about line 48 in your program

def main():
    config = ConfigParser.RawConfigParser()
    etc.

if __name__ == "__main__":
    main()

This is just a starting point.

Once you've done this, you realize that main() is really two parts: parsing the command-line interface and doing the work. You then want to refactor things to look like this.

def serverWork(group,...):
    servers = getServers(group)
    etc.

def main():
    config = ConfigParser.RawConfigParser()

    if command.strip() == "":
        parser.error('no command given')
    else:
        serverWork( options.group, options.etc., ... )

Now, you have elevated the real work to a function within this module. Your serverWork function can now be reused easily by other programs or scripts.