Re: [Tutor] calling setters of superclasses

2010-12-18 Thread Peter Otten 
Gregory, Matthew wrote:

> Hi all,
> 
> Consider the following classes where PositiveX should constrain the
> attribute _x to be positive and SmallX should further constrain the
> attribute _x to be less than 10.
> 
> class PositiveX(object):
> def __init__(self):
> self._x = 1
> @property
> def x(self):
> return self._x
> @x.setter
> def x(self, val):
> if val < 0:
> raise ValueError('Negatives not allowed')
> self._x = val
> 
> class SmallX(PositiveX):
> @property
> def x(self):
> return self._x
> @x.setter
> def x(self, val):
> # How do I call the superclass' @x.setter
> super(SmallX, self).__setattr__('x', val)
> if val > 10:
> raise ValueError('Big values not allowed')
> self._x = val
> 
> I thought I could call the superclass setter first to ensure the value was
> positive, but I'm getting an infinite recursion.  I also tried:
> 
>   super(SmallX, self).x = val
> 
> but I get this:
> 
>   AttributeError: 'super' object has no attribute 'x'
> 
> I'm fully confused and, therefore, likely doing something stupid.

I don't think /how/ you are trying it is stupid though I'm not so sure about 
/what/ .

I didn't get it to work with super() either, so here's Plan B till someone 
is going to enlighten both of us:

class SmallX(PositiveX):
@property
def x(self):
return self._x
@x.setter
def x(self, val):
if val > 10:
raise ValueError('Big values not allowed')
PositiveX.x.__set__(self, val)

Personally, I would more or less follow Alan's advice and do something like

class PositiveX(object):
def __init__(self):
self._x = 1
def check_x(self, val):
if val < 0:
raise ValueError('Negatives not allowed')
@property
def x(self):
return self._x
@x.setter
def x(self, val):
self.check_x(val)
self._x = val

class SmallX(PositiveX):
def check_x(self, val):
super(SmallX, self).check_x(val)
if val > 10:
raise ValueError('Big values not allowed')

Peter



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[Tutor] why "ifconfig" is alway running?

2010-12-18 Thread lei yang 
my script is

#!/usr/bin/env python
import datetime
import subprocess
import sys
import os
import signal
from time import sleep

def runForAWhile(cmd, secs=10):
  print("running %s" % cmd)
  timeout = datetime.timedelta(seconds=secs)
  print timeout
  proc = subprocess.Popen(cmd, stdout=subprocess.PIPE,
stderr=subprocess.STDOUT, shell=True)
  status = proc.poll()
  start = datetime.datetime.now()
  while (status is None and (datetime.datetime.now() - start) <
timeout): #not timed out
  #print proc.stdout.readline() #TODO timestamp?
  print status
  #print datetime.datetime.now() - start
  if 0 == status:
  print("'%s' is program exited" %cmd)
  else:
  try:
  os.kill(proc.pid, signal.SIGINT)
  print "Process timeout: '%s'" % cmd
  except OSError:
  pass
cmd="ifconfig"
runForAWhile(cmd,10)

why it print many "None" in 10 second. which means "ifconfig" is
running in 10sec, why, what's wrong withi my script,
I just want to let my programe running, if it's timeout(10sec), kill it

Lei
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Re: [Tutor] calling setters of superclasses

2010-12-18 Thread Hugo Arts 
On Sat, Dec 18, 2010 at 11:06 AM, Peter Otten <__pete...@web.de> wrote:
>
> I don't think /how/ you are trying it is stupid though I'm not so sure about
> /what/ .
>
> I didn't get it to work with super() either, so here's Plan B till someone
> is going to enlighten both of us:
>

By no means a solution, but I've spent some time with this in the
python debugger and have some ideas.

The problem is not super, as it does its job at calling __setattr__ of
the base object class. __setattr__, however, resolves to the x object
that is bound to self, which is SmallX.x, and not PositiveX.x, and
this is what causes the recursion.

So what you actually need is something like super(SmallX,
self).x.__set__, but that unfortunately doesn't work either since
super will use __getattr__ to resolve x, which will just result in the
property getter being called. So in general, properties don't jive
well with inheritance of their containing objects. I'm not sure if
this behavior can be considered a bug.

My idea would be to create separate descriptor classes and contain the
constraints within them. The functionality has nothing to do with the
containing class anyway, so it might actually simplify the design.
Here's the basic idea:

class UnsignedProp(object):
def __init__(self, val):
self.x = val
def __get__(self, instance, owner):
return self.x
def __set__(self, instance, val):
if val < 0: raise ValueError("Negatives not allowed")
self.x = val

class SmallProp(UnsignedProp):
def __set__(self, instance, val):
if val > 10: raise ValueError("value too large")
super(SmallProp, self).__set__(instance, val)

class X(object):
x = SmallProp(1)
y = UnsignedProp(1)

a = X()
a.x = 5
a.x = 25 # will raise ValueError
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Re: [Tutor] why "ifconfig" is alway running?

2010-12-18 Thread Alan Gauld 


"lei yang"  wrote


def runForAWhile(cmd, secs=10):
   proc = subprocess.Popen(cmd, stdout=subprocess.PIPE,

stderr=subprocess.STDOUT, shell=True)
   status = proc.poll()
   start = datetime.datetime.now()
   while (status is None and
   (datetime.datetime.now() - start) <   timeout): #not 
timed out

 print status
   if 0 == status:
 print("'%s' is program exited" %cmd)
  else:
 try:
 os.kill(proc.pid, signal.SIGINT)



why it print many "None" in 10 second. which means "ifconfig" is
running in 10sec, why, what's wrong withi my script,


You only check the status once *before* entering the while loop.
You need another status check inside the loop.

I just want to let my programe running, if it's timeout(10sec), kill 
it


Its not clear from your mail if you have checked whether the
process really is running - using the OS commands 'top' or 'ps'
for example or whjether its just the None result you are concerned
about. But try updating status first...

HTH,


--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/


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[Tutor] looking for python or django SQL data editor

2010-12-18 Thread Len Conrad 
phpmyadmin and other such mysql db design/maintain tools do too much, too 
complicated.

I'm looking for a python or django web app that allows non-tech users to 
add/delete/search records.

thanks
Len




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Re: [Tutor] looking for python or django SQL data editor

2010-12-18 Thread David Hutto 
On Sat, Dec 18, 2010 at 7:45 PM, Len Conrad  wrote:
> phpmyadmin and other such mysql db design/maintain tools do too much, too 
> complicated.
>
> I'm looking for a python or django web app that allows non-tech users to 
> add/delete/search records.

You'll probably find the same here. A bunch of functions and utilities
that are useless to the project at hand within frameworks.
Although I'm sure it would be more helpful if you start rolling your
own and asking from there.


-- 
All comments shoukd be taken with a grain of salt, and thorough review
of aforementioned material should be reviewed by the
student...understood...self learner?
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Re: [Tutor] The Template Pattern

2010-12-18 Thread Steven D'Aprano 

Karim wrote:


class InputStrategy( object ):
"""This InputStrategy class is an abstract interface to various
read strategy objects.
"""
def read(self, filePath):
"""Abstract method to load into database memory an input file.
@arg: filePath - string - The input file path.
@return: The created database object.
"""
raise NotImplementedError

By the way, I use NotImplementedError in my abstract method of the 
abstract class. You are using TypeError exception.

Is there a general rule for that? NotImplementedError is ok?



For abstract methods that should be overridden by a subclass, I would 
use NotImplementedError, as you do. That is a clear convention for 
saying "this method must be overridden".


But __init__ is a special case. The __init__ method isn't merely not 
implemented. It *is* implemented, and it does two jobs: it performs any 
common initialization for the class and all subclasses, and it also 
prevents the AbstractCLass from being instantiated.


class AbstractClass:
def __init__(self, *args):
if type(self) is AbstractClass:
raise TypeError
# do common initialization here

Trying to instantiate an AbstractClass is always an error:

instance = AbstractClass(args)

and the error is a *type* error -- you are trying to instantiate a type 
that can't be. Python already does that, with the singletons None, 
NotImplemented (different from NotImplementedError!), and Ellipsis:


>>> type(None)()
Traceback (most recent call last):
  File "", line 1, in 
TypeError: cannot create 'NoneType' instances


TypeError means you have an error in your code. NotImplementedError 
means the code is incomplete.




I knew from Java experience that template method pattern is only a 
kind of particular case of Stategy where you delegate
parts of algorithm by abstract methods overriding. Indeed the base 
class implements some common features and let

derived classes implement particular parts by polymorphism.
Now with your example, I don't understand why he had problems to 
implement from C++ ?

Or perhaps is he mixing it with C++ feature template  ?!


You'd have to ask him. Maybe he's just not a very good programmer, or 
was having a bad day.





--
Steven

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[Tutor] Python using version 3.1

2010-12-18 Thread Lea Parker 
Hello

I am working through a purchased text book Python programming for beginners.
Chapter two shows how to create a basic program using triple-quoted strings.

I am having problems working out what I have done incorrectly. The game over
block writing should stay on the same line but the bottom half of the word
over comes up next to the top half of the word over. Hope that makes sense.

My code is as follows:

# Game Over - Version 2
# Demonstrates the use of quotes in strings

print("Program 'Game Over' 2.0")

print("Same", "message", "as before")

print("Just",
  "a bit",
  "bigger")

print("Here", end=" ")

print("it is...")

print(
  """

_      __  ___
   / | /| /  |/   | |  ___|
   | |/ / | |/ /|   / | | |__
   | |  _/  |   / / |__/| | |  __|
   | |_| |  / /   | |  / /  | | | |___
   \_/ /_/|_| /_/   |_| |_|

   _  _  _   _
   / __ \ | |   / / |  ___| |  _  \
   ||  || | |  / /  | |__   | |_| |
   ||  || | | / /   |  __|  |  _  /
   ||__|| | |/ /| |___  | |  \ \
   \/ |___/ |_| |_|   \_\
   
 """
) 

input("\n\nPress the enter key to exit.") 

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Re: [Tutor] Python using version 3.1

2010-12-18 Thread Hugo Arts 
On Sun, Dec 19, 2010 at 4:42 AM, Lea Parker  wrote:
> Hello
>
> I am working through a purchased text book Python programming for beginners.
> Chapter two shows how to create a basic program using triple-quoted strings.
>
> I am having problems working out what I have done incorrectly. The game over
> block writing should stay on the same line but the bottom half of the word
> over comes up next to the top half of the word over. Hope that makes sense.
>

It's the backslashes.

A backslash at the end of a line means to disregard the newline. You
need to "escape" the backslash with another backslash. See here:

>>> print """this string \
... won't have a newline, or a slash in it"""
this string won't have a newline, or a slash in it
>>> print """this string \\
... will"""
this string \
will

The R ends in backslashes, so you need to double those up.

Hugo
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Re: [Tutor] why "ifconfig" is alway running?

2010-12-18 Thread lei yang 
#!/usr/bin/env python
import datetime
import subprocess
import sys
import os
import signal
from time import sleep

def runForAWhile(cmd, secs=10):
print("running %s" % cmd)
timeout = datetime.timedelta(seconds=secs)
print timeout
proc = subprocess.Popen(cmd, stdout=subprocess.PIPE,
stderr=subprocess.STDOUT, shell=True)
status = proc.poll()
start = datetime.datetime.now()
while (status is None and (datetime.datetime.now() - start) <
timeout): #not timed out
print proc.stdout.readline() #TODO timestamp?
#print status
#print datetime.datetime.now() - start
if 0 == status:
print("'%s' is program exited" %cmd)
else:
try:
os.kill(proc.pid, signal.SIGINT)
print "Process timeout: '%s'" % cmd
except OSError:
pass
cmd="ping 128.224.165.20 -c 4"
runForAWhile(cmd,30)


I see that "status" always "!=0“  why  program  is NOT exited

Lei



On Sun, Dec 19, 2010 at 1:15 AM, Alan Gauld  wrote:
>
> "lei yang"  wrote
>
>> def runForAWhile(cmd, secs=10):
>>   proc = subprocess.Popen(cmd, stdout=subprocess.PIPE,
>>
>> stderr=subprocess.STDOUT, shell=True)
>>   status = proc.poll()
>>   start = datetime.datetime.now()
>>   while (status is None and
>
>               (datetime.datetime.now() - start) <   timeout): #not timed out
>>
>>             print status
>>   if 0 == status:
>>     print("'%s' is program exited" %cmd)
>>  else:
>>     try:
>>         os.kill(proc.pid, signal.SIGINT)
>
>> why it print many "None" in 10 second. which means "ifconfig" is
>> running in 10sec, why, what's wrong withi my script,
>
> You only check the status once *before* entering the while loop.
> You need another status check inside the loop.
>
>> I just want to let my programe running, if it's timeout(10sec), kill it
>
> Its not clear from your mail if you have checked whether the
> process really is running - using the OS commands 'top' or 'ps'
> for example or whjether its just the None result you are concerned
> about. But try updating status first...
>
> HTH,
>
>
> --
> Alan Gauld
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
>
>
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Re: [Tutor] Python using version 3.1

2010-12-18 Thread wesley chun 
On Sat, Dec 18, 2010 at 8:13 PM, Hugo Arts  wrote:
> On Sun, Dec 19, 2010 at 4:42 AM, Lea Parker  wrote:
>> I am having problems working out what I have done incorrectly. The game over
>> block writing should stay on the same line but the bottom half of the word
>> over comes up next to the top half of the word over. Hope that makes sense.
>
> It's the backslashes.
>
> A backslash at the end of a line means to disregard the newline. You
> need to "escape" the backslash with another backslash. See here:
>
 print """this string \
> ... won't have a newline, or a slash in it"""
> this string won't have a newline, or a slash in it
 print """this string \\
> ... will"""
> this string \
> will
>
> The R ends in backslashes, so you need to double those up.


correct me if i'm wrong, but speaking of R, i think putting an 'r' or
'R' in front of the opening triple quotes to turn it into a raw string
will make it so that you *wouldn't* have to double everything up.

by the way... welcome to Python!! :-)

cheers,
-- wesley
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
"Core Python Programming", Prentice Hall, (c)2007,2001
"Python Fundamentals", Prentice Hall, (c)2009
    http://corepython.com

wesley.j.chun :: wescpy-at-gmail.com
python training and technical consulting
cyberweb.consulting : silicon valley, ca
http://cyberwebconsulting.com
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