date:20110419

Re: Can you advice a Python library to query a lan subnet with SNMP and collect MAC addresses of nodes?

2011-04-19 Thread Aldo Ceccarelli

On 18 Apr, 22:38, Daniel Kluev dan.kl...@gmail.com wrote:
 Isn't it better to use subprocess.Popen and read stdout/stderr
 directly? Should be much more convenient than temporary files.

 --
 With best regards,
 Daniel Kluev

Thanks Daniel, your solution is far better WKR! Aldo
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Re: Equivalent code to the bool() built-in function

2011-04-19 Thread Kushal Kumaran

On Tue, Apr 19, 2011 at 7:09 AM, Christian Heimes li...@cheimes.de wrote:
 Am 18.04.2011 21:58, schrieb John Nagle:
     This is typical for languages which backed into a bool type,
 rather than having one designed in.  The usual result is a boolean
 type with numerical semantics, like

   True + True
 2

 I find the behavior rather useful. It allows multi-xor tests like:

 if a + b + c + d != 1:
    raise ValueError(Exactly one of a, b, c or d must be true.)


Unless you're sure all of a, b, c, and d are boolean values, an int
with a negative value slipping in could result in the sum equaling 1,
but more than one of the variables evaluating to True in boolean
contexts.

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Re: Equivalent code to the bool() built-in function

2011-04-19 Thread Chris Angelico

On Tue, Apr 19, 2011 at 4:23 PM, Kushal Kumaran
kushal.kumaran+pyt...@gmail.com wrote:
 if a + b + c + d != 1:
    raise ValueError(Exactly one of a, b, c or d must be true.)


 Unless you're sure all of a, b, c, and d are boolean values, an int
 with a negative value slipping in could result in the sum equaling 1,
 but more than one of the variables evaluating to True in boolean
 contexts.

If they're all expressions, then you can easily guarantee that.

ChrisA
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Re: Feature suggestion -- return if true

2011-04-19 Thread Jussi Piitulainen

Gregory Ewing writes:
 Chris Angelico wrote:
 
  Question: How many factorial functions are implemented because a
  program needs to know what n! is, and how many are implemented to
  demonstrate recursion (or to demonstrate the difference between
  iteration and recursion)? :)

(I can't get to the parent directly, so I follow up indirectly.)

Factorials become an interesting demonstration of recursion when done
well. There's a paper by Richard J. Fateman, citing Peter Luschny:

http://www.cs.berkeley.edu/~fateman/papers/factorial.pdf
http://www.luschny.de/math/factorial/FastFactorialFunctions.htm

Fateman's major conclusion is that you should probably not use the
'naive' factorial programs for much of anything. I take this to
include their use as examples of recursion, unless the purpose is to
make the idea of recursion look bad.
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Re: Feature suggestion -- return if true

2011-04-19 Thread Chris Angelico

On Tue, Apr 19, 2011 at 4:42 PM, Jussi Piitulainen
jpiit...@ling.helsinki.fi wrote:
 Factorials become an interesting demonstration of recursion when done
 well. There's a paper by Richard J. Fateman, citing Peter Luschny:

 http://www.cs.berkeley.edu/~fateman/papers/factorial.pdf
 http://www.luschny.de/math/factorial/FastFactorialFunctions.htm

 Fateman's major conclusion is that you should probably not use the
 'naive' factorial programs for much of anything. I take this to
 include their use as examples of recursion, unless the purpose is to
 make the idea of recursion look bad.


And here is an algorithm which nobody needs, for the Simple-Minded only:
long factorial(long n) { return n = 1 ? 1 : n * factorial(n-1); }  Do
not use it if n  12.


I suppose the n  12 issue is based on the assumption that
sizeof(long)==4. That's not an algorithmic question, that's a return
type issue... not to mention a rather naive assumption. 64-bit
integers let you go to n == 20 (iirc), and if you go bignum, even that
simple algorithm will be fine for up to n == 500 or so without stack
issues.

But sometimes you need a simple and well-known algorithm to
demonstrate a language feature with. Maybe we should switch to
Fibonacci instead... Anyone for caramel sauce?

http://www.dangermouse.net/esoteric/chef_fib.html

(As a side point, I have become somewhat noted around the house for
always saying Fibonacci whenever caramel sauce is mentioned...)

Chris Angelico
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Re: How to create a (transparent) decorator with status information?

2011-04-19 Thread Timo Schmiade

Hey Ian,

On Mon, Apr 18, 2011 at 01:07:58PM -0600, Ian Kelly wrote:
 In the simple case, just store the state on the wrapper function itself:
 
 def call_counts(function):
   @functools.wraps(function)
   def wrapper(*args, **kwargs):
 wrapper.num_calls += 1
 return function(*args, **kwargs)
   wrapper.num_calls = 0
   return wrapper

Of course! Functions are first-class objects, so I can give them members
just as I would do with any other object. I'm still thinking too much
C++...

 If you want the state to be shared, you should probably store it in an
 object and use an instance method as the decorator:

Yes, this is the same idea that Wayne came up with. Thank you as well,
that helped me understand decorators a lot more.

Kind regards,

Timo
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Re: IDLE bug

2011-04-19 Thread Terry Reedy


On 4/19/2011 12:05 AM, harrismh777 wrote:

Are bug reports wanted here, or just in issue tracker?


If one is somewhat experienced with Python and is sure about having 
identified a bug, and is willing to search the tracker for existing 
reports and respond to questions, then report on the tracker. If one is 
new to Python and perhaps not sure, or should not be sure, then I prefer 
that one ask here for a second opinion.


--
Terry Jan Reedy

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Re: How to create a (transparent) decorator with status information?

2011-04-19 Thread Timo Schmiade

Hey Wayne,

On Mon, Apr 18, 2011 at 04:04:15PM -0700, Wayne Witzel III wrote:
 Going with the object approach, you could use Borg to give yourself the state 
 between instances you mentioned. And since you are using an object, you'll 
 have access to the data without needing to return it from the decorator.
 
 class StatefulDecorators(object):
 _state = {}
 def __new__(cls, *p, **k):
 self = object.__new__(cls, *p, **k)
 self.__dict__ = cls._state
 return self
 
 def count_calls(self, function):
 @functools.wraps(function)
 def wrapper(*args, **kwargs):
 try:
 self.calls += 1
 except AttributeError:
 self.calls = 1
 return function(*args, **kwargs)
 return wrapper

Brilliant! I didn't realize you could use member functions as
decorators, too! That way, you can easily create closures to self,
solving all the problems I was seeing.

Just one question remains now: What is a Borg in this context?

Thank you.

Timo
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Re: Questions about GIL and web services from a n00b

2011-04-19 Thread Lamont Nelson

1. Are you sure you want to use python because threading is not
good due
to the Global Lock (GIL)? Is this really an issue for multi-threaded
web services as seems to be indicated by the articles from a Google
search? If not, how do you avoid this issue in a multi-threaded process
to take advantage of all the CPU cores available?

To take advantage of the cores on your server you'll want to consider
a multi-process design instead of multi-threading. You can achieve
this with something like http://projects.unbit.it/uwsgi/, which will
allow you to manage the processes. I've used this behind apache
successfully.

2. Are there good web services frameworks available for building a REST
based service? I admit I have looked at web2py, Django, pyramid/pylons,
and a few others. SOAP seems to be pretty well supported but I'm not
finding the same for quick development of REST based services for
exchanging JSON or XML formatted data. This is probably just my n00b
status, but what tools are best for building a simple REST data exchange
API?

I've personally used Pyramid to implement REST web services with
multiple data transport formats (json, xml) for the same endpoints
with minimal fuss. It's basically as simple as returning an object
from your view and defining a renderer that knows how to translate
this object to the desired format. Look at
http://docs.pylonsproject.org/projects/pyramid/1.0/narr/renderers.html#views-which-use-a-renderer
and
http://docs.pylonsproject.org/projects/pyramid/1.0/narr/viewconfig.html#view-config-chapter
for more information.

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