``if t'' vs ``if t is not None''

[jno at glasnet.ru]

hi there,

i faced a VERY strange behaviour of if-test operation!

	   ``if t'' != ``if t is not None''
	where ``t'' is None or a class instance

i was writing a threader for a news reader.
and found occasional hangs of a routine which builds the sequence of message
numbers for "read next" operation.
digging deeper brought me strange results: replacing ``if t'' with
``if t is not None'' speeded up the things dramatically!

the call contecst:

      for x in self.keys() :
        m, t = self.mesg_list[ x ]   
        self.Sequence.append( m.num )
        if t is not None :
          t.buildSequence(i+1)
          self.Sequence.extend( t.Sequence )
          del t.Sequence ; t.Sequence = None # trash extra data

can anyone explain me such a phenomenon???

-- 
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