problem with class - get message that self is notdefined

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problem with class - get message that self is notdefined
5 answers - 1568 bytes -
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Hi Everyone,
When I try to use the class listed below, I get the statement that self
is not defined.
test=TriggerMessage(data)
var = test.decode(self.qname)
I would have thought that self would have carried forward when I grabbed
an instance of TriggerMessage.
Any ideas on this?
The class in question is:
class TriggerMessage(object):
def __init__(self,data):
"""
Unpacks the passed binary data based on the MQTCM2 format dictated in
the MQ Application Programming Reference
"""
self.data=data
self.structid=None
self.version=None
self.qname=None
self.procname=None
self.trigdata=None
self.appltype=None
self.applid=None
self.envdata=None
self.userdata=None
self.qmgr=None
def decode(self):
import struct
format='4s 4s 48s 48s 64s 4s 256s 128s 128s 48s'
size=struct.calcsize(format)
self.data=data
self.structid, self.version, self.qname, self.processname, \
self.triggerdata, self.appltype, self.applid, \
self.envdata, self.userdata, self.qmgr \
= struct.unpack(format,self.data)
- --
Thank you,
Andrew Robert
Systems Architect
Information Technologies
MFS Investment Management
Phone: 617-954-5882
E-mail: arobert (AT) mfs (DOT) com
Linux User Number: #201204
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Tutor maillist - Tutor (AT) python (DOT) org
No.1 | | 529 bytes | |
Mon, 2006-05-22 at 14:28 -0400, Andrew Robert wrote:
When I try to use the class listed below, I get the statement that
self
is not defined.

test=TriggerMessage(data)
var = test.decode(self.qname)
^^^^
Perhaps
var = test.decode()

would do what you want.

It is not clear why you are trying to use a "qname" argument when
decode's only argument is self. test.decode will bind self to the test
object.

Alan Gauld's web site has a useful discussion of P programming.
No.2 | | 2335 bytes | |
(usually best to click reply-All so that the reply goes to the list)

Mon, 2006-05-22 at 15:08 -0400, Andrew Robert wrote:
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Well inside the class is the decode function.

The decode method depends on "data" which is referenced as a global.
Perhaps data should be passed into decode as a second argument. My
edited version:

def decode(self, data):
^^^^^^
import struct
format='4s 4s 48s 48s 64s 4s 256s 128s 128s 48s'
size=struct.calcsize(format)
#self.data=data # not needed
^ ^^^^^^^^^^^^^^
self.structid, self.version, self.qname, self.processname, \
self.triggerdata, self.appltype, self.applid, \
self.envdata, self.userdata, self.qmgr \
= struct.unpack(format,data)
^^^^^ (removed self.)

In that function, several variables are defined from a struct unpack.

I am suggesting that the data to be unpacked gets passed into the decode
method as an argument:
test.decode(data)
I changed the struct.unpack call to use the data argument.

Some additional suggestions:
size is never used. perhaps you want:
assert size = <correct size>
import struct
could be moved to the top of the script and imported once

Hopefully this helps.

What I need is to get those values out.

How to do that, I am not exactly clear.

Andy

Python wrote:
Mon, 2006-05-22 at 14:28 -0400, Andrew Robert wrote:
>When I try to use the class listed below, I get the statement that
>self
>is not defined.
>
>test=TriggerMessage(data)
>var = test.decode(self.qname)
^^^^
Perhaps
var = test.decode()

would do what you want.

It is not clear why you are trying to use a "qname" argument when
decode's only argument is self. test.decode will bind self to the test
object.

Alan Gauld's web site has a useful discussion of P programming.

- --
Thank you,
Andrew Robert
Systems Architect
Information Technologies
MFS Investment Management
Phone: 617-954-5882

E-mail: arobert (AT) mfs (DOT) com
Linux User Number: #201204
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Version: GnuPG v1.4.3 (MingW32)

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No.3 | | 1579 bytes | |
When I try to use the class listed below, I get the statement that
self
is not defined.

test=TriggerMessage(data)
var = test.decode(self.qname)

I would have thought that self would have carried forward when I
grabbed
an instance of TriggerMessage.

self is a special varianble that is only defined inside of a
method of an object. It refers to the object itself (hence the name!)
Thus you cannot pass self.qname into a method unless you are
already inside another object's method.

You can read about this in more edetail in the P topic
of my tutor but I'll try to illustrate here:

class C:
def method(self,x):
self.var = x
def g(self, ):
(self.var)

class D:
def f(self, val):
print val

c = C()
c.method(42)

creates an object called c and executes its method with a
value of 42. This executes the function

C.method(c,42)

where self takes the values c and x 42
The end result is that object c has a data member
called var with the value 42

d = D()
c.g(d)

creates a new object d
calls the g method of c passing object d as argument
executes the function

C.g(c,d)

where self takes on the value c and takes on d
C.g() then calls d.f(self.var) which executes

D.f(d,c.var)

that is, the self in D.f() is d and the self in C.g() = c

I hope that makes sense.

Alan Gauld
Author of the Learn to Program web site

Tutor maillist - Tutor (AT) python (DOT) org
No.4 | | 814 bytes | |
>self is a special varianble
"special variable" could be confusing. Python has no "special
variables". "self" is used by convention.

Good point. The name self is not special it is its role that is
special.

thus

class C:
def m(s,p):
print p

c = C()
c.m(42)

Thus we define method m to have two parameters s and p
but when we call m we only pass in one argument. Python
then takes this and turns it into

C.m(c,42)

The specialness of 'self' is that although we specify it, and can
access it,
in the method definition we do not specify it in the message to the
class
that invokes the method.

Alan Gauld
Author of the Learn to Program web site

Tutor maillist - Tutor (AT) python (DOT) org
No.5 | | 842 bytes | |
Alan Gauld wrote:
>When I try to use the class listed below, I get the statement that
>self
>is not defined.
>>
>test=TriggerMessage(data)
>var = test.decode(self.qname)
>>
>I would have thought that self would have carried forward when I
>grabbed
>an instance of TriggerMessage.
>
>
self is a special varianble
"special variable" could be confusing. Python has no "special
variables". "self" is used by convention. could use "this" as an
alternative, or any other variable. When defining a method in a class
one writes def abc(self, a,b,c) R def abc(this, a,b,c). Then one refers
to "self" or "this" within the method to refer to the instance calling
the method.

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problem with class - get message that self is notdefined