foo found True stack list while len stack elem stack pop print Trying

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a = ((1, 2), 3, (4, 5))
foo = 4
found = True
stack = list(a)
while len(stack):
elem = stack.pop(0)
print 'Trying %s', elem
if isinstance(elem, tuple):
stack.extend(elem)
else:
if elem == foo:
break
else:
found = False
print found