[Python-bugs-list] [ python-Feature Requests-519227 ] hook method for 'is' operator

[noreply@sourceforge.net]

Feature Requests item #519227, was opened at 2002-02-18 09:12
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http://sourceforge.net/tracker/?func=detail&atid=355470&aid=519227&group_id=5470

Category: Python Interpreter Core
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Dan Parisien (mathematician)
Assigned to: Nobody/Anonymous (nobody)
Summary: hook method for 'is' operator

Initial Comment:
Being able to overload the 'is' operator would lead 
to nicer more readable code:

# constant
Open = ("OPEN",)

# dummy class for my example
class File:
	id = 0
	def __init__(self, file=None):
		if file is not None:
			self.open(file)

	# overload 'is' operator
	def __is__(self, other):
		if id(self)==id(other): # default
			return 1
		elif other==("OPEN",) and self.id!=0:
			return 1
		return 0

	def open(self, file):
		self.id = open(file).fileno

f = File("myfile.txt")
if f is Open:
	print "File is open!"
else:
	print "File is not open"

'is not' could just test __is__ and return 'not 
retval'




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>Comment By: Dan Parisien (mathematician)
Date: 2002-02-18 09:50

Message:
Logged In: YES 
user_id=118203

You can say the same for all the operators in python. The 
default behavior would be object identity, but:

x is y

is the same as doing

id(x)==id(y)

So the 'is' operator is actually superfluous except for 
its readability value.

Your comment seems to me like a knee jerk resistance to 
change. Now if you were to tell me that it would make 
python drastically slower or that it would be difficult to 
implement, then you would have a good point...



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Comment By: Neil Schemenauer (nascheme)
Date: 2002-02-18 09:30

Message:
Logged In: YES 
user_id=35752

The "is" operator has well defined semantics.  It compares
object identity.  Allowing it to be redefined would a terrible
idea, IMHO.

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