doctests = """
Unpack tuple
>>> t = (1, 2, 3)
>>> a, b, c = t
>>> a == 1 and b == 2 and c == 3
True
Unpack list
>>> l = [4, 5, 6]
>>> a, b, c = l
>>> a == 4 and b == 5 and c == 6
True
Unpack implied tuple
>>> a, b, c = 7, 8, 9
>>> a == 7 and b == 8 and c == 9
True
Unpack string... fun!
>>> a, b, c = 'one'
>>> a == 'o' and b == 'n' and c == 'e'
True
Unpack generic sequence
>>> class Seq:
... def __getitem__(self, i):
... if i >= 0 and i < 3: return i
... raise IndexError
...
>>> a, b, c = Seq()
>>> a == 0 and b == 1 and c == 2
True
Single element unpacking, with extra syntax
>>> st = (99,)
>>> sl = [100]
>>> a, = st
>>> a
99
>>> b, = sl
>>> b
100
Now for some failures
Unpacking non-sequence
>>> a, b, c = 7
Traceback (most recent call last):
...
TypeError: cannot unpack non-iterable int object
Unpacking tuple of wrong size
>>> a, b = t
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 2)
Unpacking tuple of wrong size
>>> a, b = l
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 2)
Unpacking sequence too short
>>> a, b, c, d = Seq()
Traceback (most recent call last):
...
ValueError: not enough values to unpack (expected 4, got 3)
Unpacking sequence too long
>>> a, b = Seq()
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 2)
Unpacking a sequence where the test for too long raises a different kind of
error
>>> class BozoError(Exception):
... pass
...
>>> class BadSeq:
... def __getitem__(self, i):
... if i >= 0 and i < 3:
... return i
... elif i == 3:
... raise BozoError
... else:
... raise IndexError
...
Trigger code while not expecting an IndexError (unpack sequence too long, wrong
error)
>>> a, b, c, d, e = BadSeq()
Traceback (most recent call last):
...
test.test_unpack.BozoError
Trigger code while expecting an IndexError (unpack sequence too short, wrong
error)
>>> a, b, c = BadSeq()
Traceback (most recent call last):
...
test.test_unpack.BozoError
Allow unpacking empty iterables
>>> () = []
>>> [] = ()
>>> [] = []
>>> () = ()
Unpacking non-iterables should raise TypeError
>>> () = 42
Traceback (most recent call last):
...
TypeError: cannot unpack non-iterable int object
Unpacking to an empty iterable should raise ValueError
>>> () = [42]
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 0)
"""
__test__ = {'doctests' : doctests}
def test_main(verbose=False):
from test import support
from test import test_unpack
support.run_doctest(test_unpack, verbose)
if __name__ == "__main__":
test_main(verbose=True)