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From: Frederic Weisbecker on 24 Feb 2010 20:40
On Wed, Jan 27, 2010 at 02:28:03AM -0600, Tom Zanussi wrote:
> +from perf_trace_context import *
> +from Core import *
> +
> +def trace_end():
> + print "in trace_end"
> +
> +def raw_syscalls__sys_enter(event_name, context, common_cpu,
> + common_secs, common_nsecs, common_pid, common_comm,
> + id, args):
> +----
> +
> +In trace_end(), we'll simply print the results, but first we need to
> +generate some results to print. To do that we need to have our
> +sys_enter() handler do the necessary tallying until all events have
> +been counted. A hash table indexed by syscall id is a good way to
> +store that information; every time the sys_enter() handler is called,
> +we simply increment a count associated with that hash entry indexed by
> +that syscall id:
> +
> +----
> + syscalls = autodict()
> +
> + try:
> + syscalls[id] += 1
> + except TypeError:
> + syscalls[id] = 1
> +----
> +
> +The syscalls 'autodict' object is a special kind of Python dictionary
> +(implemented in Core.py) that implements Perl's 'autovivifying' hashes
> +in Python i.e. with autovivifying hashes, you can assign nested hash
> +values without having to go to the trouble of creating intermediate
> +levels if they don't exist e.g syscalls[comm][pid][id] = 1 will create
> +the intermediate hash levels and finally assign the value 1 to the
> +hash entry for 'id' (because the value being assigned isn't a hash
> +object itself, the initial value is assigned in the TypeError
> +exception. Well, there may be a better way to do this in Python but
> +that's what works for now).


That's smart. I wish python had a native type for that.

And looking how you made it easily....

def autodict():
return defaultdict(autodict)

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