[Patches] [ python-Patches-421922 ] Restrict dict comparison to Py_EQ

[noreply@sourceforge.net]

Patches item #421922, was updated on 2001-05-06 20:10
You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=305470&aid=421922&group_id=5470

Category: core (C code)
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Tim Peters (tim_one)
Assigned to: Guido van Rossum (gvanrossum)
Summary: Restrict dict comparison to Py_EQ

Initial Comment:
Dict comparison currently requires that the keys and 
values enjoy a total ordering, but dicts only require 
Py_EQ in other contexts.  The patch changes dict 
compares to rely on just Py_EQ too, and replaces the 
cmp()-like calls with comparison of raw object 
addresses.  Besides yielding a huge speedup on an 
artificial test case <wink>, it stops surprises like 
these:

>>> {1: 1j} == {1: 2j}
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: cannot compare complex numbers using <, <=, 
>, >=
>>> {1j: 0} == {2j: 0}
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: cannot compare complex numbers using <, <=, 
>, >=
>>>

After the patch:

>>> {1: 1j} == {1: 2j}
0
>>> {1j: 0} == {2j: 0}
0
>>> cmp({1: 1j}, {1: 1j})
0
>>> cmp({1j: 0}, {1j: 0})
0
>>>


----------------------------------------------------------------------

>Comment By: Guido van Rossum (gvanrossum)
Date: 2001-05-07 06:17

Message:
Logged In: YES 
user_id=6380

I have one question about this.  Will the comparison between
dicts using cmp() or <, <=, >, >= also depend on the raw
object address?  That would mean that (even in one program)
there could be two pairs of dictionaries (A,B) and (C,D)
where A<B and C>D while A==C and B==D.  I'm not sure I like
that.

What's the real use case where this matters?  (Either the
speed of == comparisons or the ability to ==-compare dicts
containing complex numbers.)

----------------------------------------------------------------------

You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=305470&aid=421922&group_id=5470