code coverage tool

Dave Brueck dave at
Mon Mar 3 23:48:29 CET 2003

On Mon, 3 Mar 2003, John Roth wrote:

> "Dave Brueck" <dave at> wrote in message
> > > The first few messages seem not to have made it to my news server.
> > > Look on the Vaults for PyCover. It mostly does what you
> > > want, and if it doesn't, it's easy enough to change.
> >
> > No automatic support for multithreaded programs though, right?
> I'm not sure what you mean by support for multi-threaded programs.

Ever tried tracing/profiling a multithreaded program in Python? Try it and
you'll know what I mean. ;-) (see below)

> Python's threading model is to have the interpreter switch back
> and forth between its "threads" using a byte code count, so I'd assume
> that all you would need to do would be to put a monitor or something
> equivalent in the trace exits.

It's not that simple - new threads don't inherit the trace/profile hooks
from parent threads. Basically what happens is you get profile/coverage
data for the parent thread and that's it - not very useful.

One approach is to introduce a "shim" in threading and hook into
sys.settrace yourself (so that you don't have to manually set the new
trace/profile function each time you create a thread) but when I tried it
the resulting program was too darn slow - a pure Python profiler per
thread was too much I guess (maybe for code coverage it wouldn't be so
bad). Last time I tried using the same approach with the hotshot profiler
(the one written partially in C) Python crashed a lot. Oh well. :)


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