Mapping None. Why?

Ian Kelly ian.g.kelly at
Fri Jun 13 22:13:32 CEST 2008

On Fri, Jun 13, 2008 at 2:00 PM, Terry Reedy <tjreedy at> wrote:
> filter(None, iterable) works the same way: None-> identity function,
> The immediate reason is the Python has no builtin id().
> But apparently there is also historical precedent in the functional
> community for this convention.

Another way of viewing it is that filter(None, iterable) applies no
function at all before testing the truth values, which does make some
sense.  With map, however, this is not strictly true.

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