"in" for dicts (was: Python 2.1 function attributes)

[Terry Reedy]

> The only reason to like .xreadlines() is speed -- but, again, that's
reason enough.

Comparers of Perl and Python constantly notice that Perl is (was?) faster
in its equivalent of the new 'for l in f.xreadlines()'.  My first thought
was 'hope this is enough faster to quiet some of the noise.

Python won't be the first system to optimize a common 'benchmark'.