doctests = """
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Unpack tuple
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>>> t = (1, 2, 3)
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>>> a, b, c = t
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>>> a == 1 and b == 2 and c == 3
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True
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Unpack list
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>>> l = [4, 5, 6]
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>>> a, b, c = l
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>>> a == 4 and b == 5 and c == 6
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True
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Unpack implied tuple
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>>> a, b, c = 7, 8, 9
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>>> a == 7 and b == 8 and c == 9
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True
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Unpack string... fun!
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>>> a, b, c = 'one'
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>>> a == 'o' and b == 'n' and c == 'e'
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True
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Unpack generic sequence
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>>> class Seq:
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... def __getitem__(self, i):
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... if i >= 0 and i < 3: return i
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... raise IndexError
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...
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>>> a, b, c = Seq()
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>>> a == 0 and b == 1 and c == 2
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True
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Single element unpacking, with extra syntax
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>>> st = (99,)
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>>> sl = [100]
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>>> a, = st
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>>> a
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99
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>>> b, = sl
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>>> b
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100
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Now for some failures
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Unpacking non-sequence
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>>> a, b, c = 7
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Traceback (most recent call last):
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...
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TypeError: 'int' object is not iterable
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Unpacking tuple of wrong size
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>>> a, b = t
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Traceback (most recent call last):
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...
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ValueError: too many values to unpack
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Unpacking tuple of wrong size
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>>> a, b = l
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Traceback (most recent call last):
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...
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ValueError: too many values to unpack
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Unpacking sequence too short
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>>> a, b, c, d = Seq()
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Traceback (most recent call last):
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...
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ValueError: need more than 3 values to unpack
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Unpacking sequence too long
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>>> a, b = Seq()
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Traceback (most recent call last):
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...
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ValueError: too many values to unpack
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Unpacking a sequence where the test for too long raises a different kind of
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error
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>>> class BozoError(Exception):
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... pass
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...
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>>> class BadSeq:
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... def __getitem__(self, i):
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... if i >= 0 and i < 3:
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... return i
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... elif i == 3:
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... raise BozoError
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... else:
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... raise IndexError
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...
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Trigger code while not expecting an IndexError (unpack sequence too long, wrong
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error)
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>>> a, b, c, d, e = BadSeq()
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Traceback (most recent call last):
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...
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BozoError
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Trigger code while expecting an IndexError (unpack sequence too short, wrong
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error)
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>>> a, b, c = BadSeq()
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Traceback (most recent call last):
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...
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BozoError
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"""
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__test__ = {'doctests' : doctests}
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def test_main(verbose=False):
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from test import test_support
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from test import test_unpack
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test_support.run_doctest(test_unpack, verbose)
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if __name__ == "__main__":
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test_main(verbose=True)
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