speedup up dictionary access

[Roy Smith]

One of the big time consumers in an application I'm writing is a cache 
lookup in the inner loop of the program.  Right now, it looks something 
like this:

   if (self.cache.has_key (name) and self.cache[name]) or self.check (name):
      do stuff

check() returns 0 or 1 based on the value of name, and also inserts this 
value into the cache.

I know that my cache hit ratio is going to be very high (almost 100%).  
Would I do better writing it as:

   try:
      if self.cache[name]:
         do stuff
   except KeyError:
      if self.check (name):
         do stuff

In the first style, I've got the overhead of doing a has_key() call which 
99% of the time will return 1.  In the second style, I've got the overhead 
of setting up a try block.  Which is faster?