[ python-Bugs-1569356 ] sys.settrace cause curried parms to show up as attributes

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Bugs item #1569356, was opened at 2006-10-02 11:26
Message generated for change (Comment added) made by scott_marks
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Category: Python Interpreter Core
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: applebucks (scott_marks)
Assigned to: Nobody/Anonymous (nobody)
Summary: sys.settrace cause curried parms to show up as attributes

Initial Comment:
The code below exhibits different behavior depending on
whether it invokes sys.settrace ('-t' option) or not. 
This means that (in a more complicated case) debugging
the code (which uses sys.settrace) makes it fail. 
Reported v 2.4, but the same behavior on 2.5.  Any ideas?

""" Demonstrace that tracing messes up curried class
definitions """

# Some simple command line parsing: -t or --trace means
trace, nothing means don't trace
import sys

def usage( ):
    print 'Usage:', sys.argv[ 0 ], '[-t | --trace]'
    sys.exit( 1 )

if 1 == len( sys.argv ):
    pass
elif 2 == len( sys.argv ):
    if sys.argv[ 1 ]=='-t' or sys.argv[ 1 ]=='--trace':
        def trace ( frame, event, arg ):
            # print frame, event, arg
            return trace
        sys.settrace( trace )
    else:
        usage( )
else:
    usage( )



# The test: define a class factory with a curried
member function

def the_factory( parm1 ):
    class the_class( object ):
        def curried( self ): return parm1
    return the_class

x = the_factory( 42 )

y = x( )

try:
    x.parm1
    print "Failure: x (the manufactured class) has
attribute parm1?!"
except AttributeError:
    print "Success with the manufactured class!"

try:
    y.parm1
    print "Failure: y (the instance) has attribute parm1?!"
except AttributeError:
    print "Success with the instance!"

assert y.curried( ) == 42, "Currying didn't work?!" 

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>Comment By: applebucks (scott_marks)
Date: 2006-10-02 12:02

Message:
Logged In: YES 
user_id=120857

This bug actually causes a failure in a system that heavily
uses function-level programming and member delegation.  The
bug occurred when a class factory function formal parameter
name was the same as a field delegated by instances of the
generated class to a member -- when run in a debugger (i.e.
after a non-None call to sys.settrace) the delegating
descriptor was over-written by the value of the factory
function parameter.

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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1569356&group_id=5470