Python Class For Reading List Element ,str and class questions

Question

I am writing a Python script which will ssh into a box(using parakimo) and run a command. I wanted to make a object for the stdout/stderr and print out the output.

Am I passing the list correctly into the class? and am I handing the list correctly in the class?
I want to utilize the __str__ method so I can just print(object). How can I do this correctly?
I intend to use 2 instances of this class because I will be doing 2 separate sss.exec_command(command). Am I wasting memory by wrapping this function in a class? I wanted to utilize the OO to be efficient, organized, and try to utilize python's OO features.

class read_log:
    def __init__(self, exit_status, *tuple_list):
        self.exit_status = exit_status
        self.tuple_list = tuple_list
        if exit_status:
            output = stderr.readlines()
        else:
            output =  stdout.readlines()
            del output[0]
            del output[-1]
    def __str__(self) 
        return ''.join(output)    

def create():
    stdin, stdout, stderr=ssh.exec_command("/home/one/script.sh")
    exit_status = stdout.channel.recv_exit_status()
    x = readlog(exit_status, stdin, stdout, stderr)
    print(x)

Martijn Pieters · Accepted Answer · 2013-05-17 20:46:10Z

1

You capture the stdin, stdout and stderr inputs as one catch-all argument, but then try to refer to those names again in the __init__ function.

Just make them separate parameters:

class read_log:
    def __init__(self, exit_status, stdin, stdout, stderr):
        self.exit_status = exit_status
        self.tuple_list = (stdin, stdout, stderr)

Use *args syntax when you need to allow for a variable number of arguments, not for catching a fixed number of arguments that you then otherwise not use. I stored the 3 arguments as a tuple onto your instance anyway, in case you are using self.tuple_list elsewhere.

You need to store output on the instance:

if exit_status:
    self.output = stderr.readlines()
else:
    self.output =  stdout.readlines()
    del self.output[0]
    del self.output[-1]

and in __str__ refer to that instance attribute:

def __str__(self) 
    return ''.join(self.output)

The latter del statements can also be replaced with a slice:

if exit_status:
    self.output = stderr.readlines()
else:
    self.output =  stdout.readlines()[1:-1]

edited May 17, 2013 at 20:46

answered May 17, 2013 at 20:40

Martijn Pieters

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2 Comments

dman Over a year ago

I keep getting <__main__.ReadLog instance at 0x7f39fd648878>. Why is this? By the way, I changed the class name to ReadLog instead of read_log. Also, what exactly is std* objects?

Martijn Pieters Over a year ago

That is the repr() representation if your instance. Use print or str() to see your __str__ method at work, or define a __repr__ method to override the result of repr(). The std* objects are file streams, the default ('standard' or 'std') input, output and error streams all processes on UNIX systems have.

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