[Python-Dev] Comparison speed

[Jeremy Hylton]

I only learned recently that isinstance() can be called with types
instead of classes.  I suppose the name lead me in the wrong
direction.  I had the silly idea that it only applied to instances
<0.1 wink>.

So it comes as little surprise to me that there is a lot of code
executed in, e.g., the test suite that does comparisons on types.

In the Lib directory, there are 63 files that use == and the builtin
type function.  (Simple grep.)  A total of 139 instances of this
idiom.  A cursory scan suggests that most of the call are things like
type(obj) == type('').

In the Zope source tree, there are 58 files and 98 individual
occurrences.  It again looks like comparisons against string type is
the most common.

I can think of two common cases where an object is checked against the
string type.  One is an interface that takes a file-like object or its
path.  The other is an interface that takes a sequence, but doesn't
want to try a string as a sequence.

Sounds like we ought to do a search-and-destroy on type comparisons,
replacing with isinstance() where possible.

Jeremy