[Python-Dev] redefining is (original) (raw)

Michael Chermside mcherm at mcherm.com
Fri Mar 19 14:25:47 EST 2004

Barry writes:

Using == for identity objects is the wrong thing. We should discourage tests like "if obj == None" in favor of "if obj is None".

I hear you, but I disagree. There is a good reason why the default implementation of '==' compares by object identity.

I don't care much whether we use "if obj is None" rather than "if obj == None", since the PARTICULAR case of comparing with None is mostly just an idiom. But if you have two different identity objects and want to compare them, then I would prefer

if currentCustomer == desiredCustomer:

to

if currentCustomer is desiredCustomer:

However, either one works, and I won't gripe about your using 'is' if you prefer it. I WOULD gripe if you overrode eq to raise an exception in order to force me to use 'is' not '==' on your objects (not that you ever suggested doing so).

-- Michael Chermside

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