传递和处理函数参数的最佳方法

Question

After some reading, I found myself struggling with two different approaches to pass a list of arguments to a function. I read some indications. That's what I figured out so far:

Actual code:

file caller.py:

import worker
worker.version_check(iserver,login,password,proxyUser,proxyPass,
  proxyServer,packageInfo)

worker.version_get(iserver,login,password,proxyUser,proxyPass,
  proxyServer,packageInfo)

worker.version_send(iserver,login,password,proxyUser,proxyPass,
  proxyServer,packageInfo)

File: worker.py:

def version_check(iserver,login,password,proxyUser,proxyPass,proxyServer,service):
    #code and more code

def version_get(iserver,login,password,proxyUser,proxyPass,proxyServer,service):
     #code and more code

def version_send(iserver,login,password,proxyUser,proxyPass,proxyServer,service):
    #code and more code

And now I have:

file caller.py:

import worker
args = (env, family, host, password, prefix, proxyServer,
        proxyUser, proxyPass, option, jokerVar
       )
worker.version_check(*args)
worker.version_get(*args)
worker.version_send(*args)

File: worker.py:

def version_check(*args):
  env = args[0]
  family = args[1]
  host = args[2]
  password = args[3]
  prefix = args[4]
  proxyServer = args[5]
  proxyUser = args[6]
  proxyPass = args[7]
  option = args[8]
  jokerVar = args[9]

  #code and more code

def version_get((*args):
  env = args[0]
  family = args[1]
  host = args[2]
  password = args[3]
  prefix = args[4]
  proxyServer = args[5]
  proxyUser = args[6]
  proxyPass = args[7]
  option = args[8]
  jokerVar = args[9]

  #code and more code

def version_send(*args):
  env = args[0]
  family = args[1]
  host = args[2]
  password = args[3]
  prefix = args[4]
  proxyServer = args[5]
  proxyUser = args[6]
  proxyPass = args[7]
  option = args[8]
  jokerVar = args[9]

  #code and more code

Using the old approach (actual code) I believe it is more "friendly" to call a function in one line only (as you can see on worker.py). But, using the new approach, I think the code get more extensive because for each function I have to define all the same variables. But is this the best practice? I'm still learning Python on a slow curve, so, sorry for any mistakes in the code.

And one important thing, most of the variables are retrieved from a database, so they are not stactic.

Answer 1

I really don't recommend defining functions like def version_check(*args): unless you specifically need to. Quick, without reading the source: what order are the arguments in? How do you specify a default value for proxyServer? Remember, "explicit is better than implicit".

The one time I routinely deviate from that rule is when I'm wrapping another function like:

def foo(bar):
    print 'Bar:', bar

def baz(qux, *args):
    print 'Qux:', qux
    foo(*args)

I'd never do it for such a simple example, but suppose foo is a function from a 3rd-party package outside my control with lots of defaults, keyword arguments, etc. In that case, I'd rather punt the argument parsing to Python than attempt it myself.

Personally, I'd write that as a class like:

class Worker(object):
    def __init__(iserver,login,password,proxyUser,proxyPass,proxyServer,service):
        self.iserver = iserver
        self.login = login
        self.password = password
        self.proxyUser = proxyUser
        self.proxyPass = proxyPass
        self.proxyServer = proxyServer
        self.service = service

    def version_check(self): ...

    def version_get(self): ...

    def version_send(self): ...

And then in the client, write:

from worker import Worker

w = Worker(iserver,login,password,proxyUser,proxyPass,proxyServer,service)
w.version_check()
w.version_get()
w.version_send()

If you really need to write functions with lots of arguments instead of encapsulating that state in a class - which is a more typically Pythonic way to do it - then consider the namedtuple datatype from recent Python versions. It lets you specify a tuple where items are addressable by keyword and can make for some very clean, elegant code.

Answer 2

There are many approaches, depending on what those arguments represent.

1. If they are just a grab-bag of arguments (especially if some are optional), use keyword arguments :

    myargs = {'iserver':'server','login':'username','password':'Pa2230rd'} version_get(**myargs) 

2. If they represent some thing with its own state, then use classes :

   1. If the arguments represent a single state that your functions are modifying, then accept the arguments in the object constructor and make your version_* methods functions of that class:

       class Version(object): def __init__(self,iserver,login,password, proxyUser,proxyPass,proxyServer,service): self.iserver = iserver self.login = login #etc def check(self): self.iserver def get(self): pass #etc myversion = Version('iserver','login',...) myversion.check() 

   2. If you have some kind of resource those arguments represent that your functions are merely using, in that case use a separate class, and supply it as an object parameter to your functions:

       class Connection(Object): def __init__(self, iserver, ...): self.iserver # etc myconn = Connection('iserver',...) version_check(myconn) 

   3. Most likely, these are two different resources and should be two classes. In this case you can combine these approaches:

       #Connection() class as above class Version(object): def __init__(self, connection): self.connection = connection def check(self): self.connection.iserver # .... myconn = Connection('iserver', ...) conn_versioner = Version(myconn) conn_versioner.check() 

   4. Possibly, your arguments represent more than one object (eg, a connection and a transparent proxy object) In that case, try to create an object with the smallest public interface methods like version_* would need and encapsulate the state represented by the other arguments using object composition.

      For example, if you have proxy connections, you can create a Connection() class which just knows about server, login and password, and a ConnectionProxy() class which has all the methods of a Connection , but forwards to another Connection object. This allows you to separate the proxy* arguments, and means that your version_* functions can be ignorant of whether they're using a proxy or not.

3. If your arguments are just state and don't have any methods proper to them, consider using a namedtuple() . This will act like a smarter tuple (including tuple unpacking, slicing, etc) and have minimal impact on your existing code while still being easier to use.

    Connection = namedtuple('Connection', 'iserver login password etc') myconn = Connection('iserver', 'loginname', 'passw3rd') version_check(*myconn) 

Answer 3

You can create instance an object or define a class. eg

file caller.py:

import worker

info=object()
info.env=0
info.family='something'
info.host='something'
info.password='***'
info.prefix=''
info.proxyServer=''
info.proxyUser=''
info.proxyPass=''
info.option=''
info.jokerVar=''

worker.version_check(info)
worker.version_get(info)
worker.version_send(info)

file worker.py:

def version_check(info):
    #you may access values from info
    #code and more code

def version_get(info):
    #code and more code

def version_send(info):
    #code and more code