Re: Setting a read-only attribute

tleeuwenburg@xxxxxxxxx wrote:
On Aug 31, 6:14 pm, Alexandre Badez <alexandre.ba...@xxxxxxxxx> wrote:
On Aug 30, 11:35 pm, "tleeuwenb...@xxxxxxxxx" <tleeuwenb...@xxxxxxxxx>
wrote:

I have an object and wish to set an attribute on it which,
unfortunately for me, is read-only.
How can I go about this?
Cheers.
-T
Could you show the object you want to set his attribute?
Until that, it's difficult to answer to you.

PS: If the attribut is on read only, their must a good reason for
that ;)

Hi all,

Thanks for all the responses. What I'm trying to do is kludge around
something. sys.settrace takes a method whose arguments are (frame,
event, arg). I want to have a tracer class which can be instantiated
and listen in on these trace calls.

Another way to go about it *might* be to have a module-level list of
registered Tracer objects which a module-level trace method informs of
events. It would probably be easier. In fact, I'll go do that.

*That said*, I still think it makes sense to be able to have objects
register with sys.settrace.

So what I did then was declare a static method with the same pattern
expected by sys.settrace. I then want to use something like __dict__
or __setattr__ to give that method a reference to the owning object.
And this is what I'm trying to do -- declare a static method, then "un-
static it" by adding a reference to the callable object...

Here's some code:
------------------------------------------------------------

import sys


class Tracer:
'''
Instantiate this in order to access program trace information.

'''

def _getcallback(self):

@staticmethod
def callback(frame, event, arg):
print "tracing ...", tracerReference
#print "line ", frame.f_lineno, frame.f_locals

return callback

def startTrace(self):
callback = self._getcallback()
callback.__dict__['tracerReference'] = self
sys.settrace(callback)


def foo(dict):
for i in range(2):
pass

if __name__ == "__main__":
t = Tracer()
t.startTrace()
foo({1 : 5})

Surely the thing to do, if I understand you, is to declare callback as a standard method and then pass a reference to a bound method (the most obvious candidate being self.callback) to sys.settrace().

sholden@bigboy ~/Projects/Python
$ cat test05.py
import sys


class Tracer:
'''
Instantiate this in order to access program trace information.

'''


def callback(self, frame, event, arg):
print "tracing ...", self
print "line ", frame.f_lineno, frame.f_locals

def startTrace(self):
sys.settrace(self.callback)


def foo(dict):
for i in range(2):
pass

if __name__ == "__main__":
t = Tracer()
t.startTrace()
foo({1 : 5})

sholden@bigboy ~/Projects/Python
$ python test05.py
tracing ... <__main__.Tracer instance at 0x7ff2514c>
line 19 {'dict': {1: 5}}

sholden@bigboy ~/Projects/Python
$

Does this do what you want?

regards
Steve
--
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