The following code doesn't work correctly if the
function "generator()" doesn't have any values.

if generator():
  print "This should only happen when the generator
runs yield"
  print " but it is always true, even if the generator
is empty"
else:
  print "this is the expected path when the generator
is empty"

The workaround is:

try:
  generator().next()
  print "this is the true case"
except StopIteration:
  print "this is the false case"

This means that generators are not transparent and they
don't behave as expected (like a list or tuple).

I've been bitten by this enough that I am unhappy. :-(

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user_id=80475

Your unhappiness is predicated on an invalid set of
assumptions.  For most generators, it is not possible to
know in advance whether the iterator will raise
StopIteration on the next call.

Also, Guido has pronounced that generators (like most
objects) will always evaluate to True.