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

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