recursion in __cmp__

[Victor Safronovich]

please comment this
Python 2.2.3 (#42, May 30 2003, 18:12:08) [MSC 32 bit (Intel)] on win32

class A: def __cmp__(self, other):
print '%s|%s' %(`self`, `other`)
return cmp(self, other)
a = A()
cmp(a,A()) <__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
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0 cmp(a,5)

<__main__.A instance at 0x00989838>|5
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0

[Alex Martelli]

Victor Safronovich <vs**********@naumen.ru> wrote:

please comment this
Python 2.2.3 (#42, May 30 2003, 18:12:08) [MSC 32 bit (Intel)] on win32

class A:

def __cmp__(self, other):
print '%s|%s' %(`self`, `other`)
return cmp(self, other)

What is there to comment? This is obviously and blatantly recursive,
since cmp(a, b) delegates back to a.__cmp__(b) [[for classic classes;
for a newstyle class it would be type(a).__cmp__(a, b) with the same
recursive effect in this case]].

Just like the simpler example: def __len__(self): return len(self)
Alex

[John Doe]

Really Victor,
no one comments on old versions. Try it on 2.3.

Dan

On Fri, 05 Nov 2004 00:45:28 -0800, Victor Safronovich wrote:

please comment this
Python 2.2.3 (#42, May 30 2003, 18:12:08) [MSC 32 bit (Intel)] on win32

class A: def __cmp__(self, other):
print '%s|%s' %(`self`, `other`)
return cmp(self, other)
a = A()
cmp(a,A()) <__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
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<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
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<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
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<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
<__main__.A instance at 0x00989838>|<__main__.A instance at 0x0097D120>
0 cmp(a,5)

<__main__.A instance at 0x00989838>|5
<__main__.A instance at 0x00989838>|5
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0

[Peter Otten]

Victor Safronovich wrote:

please comment this
Python 2.2.3 (#42, May 30 2003, 18:12:08) [MSC 32 bit (Intel)] on win32

class A: def*__cmp__(self,*other):
print*'%s|%s'*%(`self`,*`other`)
return*cmp(self,*other)
a = A()
cmp(a,A())
Does it get clearer with the following reimplementation of cmp()?
class A: .... def __cmp__(self, other):
.... return mycompare(self, other)
.... def mycompare(a, b): .... try:
.... return a.__cmp__(b)
.... except AttributeError:
.... return mycompare(id(a), id(b))
.... mycompare(A(), A()) Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 3, in mycompare
File "<stdin>", line 3, in __cmp__
File "<stdin>", line 3, in mycompare
File "<stdin>", line 3, in __cmp__
[snip]
File "<stdin>", line 3, in __cmp__
File "<stdin>", line 3, in mycompare
RuntimeError: maximum recursion depth exceeded

Peter