[Python-Dev] "and" and "or" operators in Py3.0
reinhold-birkenfeld-nospam at wolke7.net
Tue Sep 20 11:22:29 CEST 2005
Raymond Hettinger wrote:
> I propose that in Py3.0, the "and" and "or" operators be simplified to
> always return a Boolean value instead of returning the last evaluated
No, please not. It's useful sometimes and doesn't hurt most times.
> 1) The construct can be error-prone. When an error occurs it can be
> invisible to the person who wrote it. I got bitten in published code
> that had survived testing and code review:
> def real(self):
> 'Return a vector with the real part of each input element'
> # do not convert integer inputs to floats
> return self.map(lambda z: type(z)==types.ComplexType and z.real or
I'm surprised you wrote that in the first place. The "and/or conditional"
is one of the few occurences where one will carefully look for false values
in the "and" part.
> The code fails silently when z is (0+4i). It took a good while to trace
> down a user reported error (when Matlab results disagreed with my matrix
> module results) and determine that the real() method contained an error.
> Even when traced down, I found it hard to see the error in the code.
> Now that I know what to look for, it has not happened again, but I do
> always have to stare hard at any "and/or" group to mentally verify each
> P.S. Simplifying "and" and "or" may create a need to introduce a
> conditional operator but that is a discussion for another day.
Exactly. A conditional was turned down some time ago, for good reasons.
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