1 doctests = """ 2 3 Unpack tuple 4 5 >>> t = (1, 2, 3) 6 >>> a, b, c = t 7 >>> a == 1 and b == 2 and c == 3 8 True 9 10 Unpack list 11 12 >>> l = [4, 5, 6] 13 >>> a, b, c = l 14 >>> a == 4 and b == 5 and c == 6 15 True 16 17 Unpack implied tuple 18 19 >>> a, b, c = 7, 8, 9 20 >>> a == 7 and b == 8 and c == 9 21 True 22 23 Unpack string... fun! 24 25 >>> a, b, c = 'one' 26 >>> a == 'o' and b == 'n' and c == 'e' 27 True 28 29 Unpack generic sequence 30 31 >>> class Seq: 32 ... def __getitem__(self, i): 33 ... if i >= 0 and i < 3: return i 34 ... raise IndexError 35 ... 36 >>> a, b, c = Seq() 37 >>> a == 0 and b == 1 and c == 2 38 True 39 40 Single element unpacking, with extra syntax 41 42 >>> st = (99,) 43 >>> sl = [100] 44 >>> a, = st 45 >>> a 46 99 47 >>> b, = sl 48 >>> b 49 100 50 51 Now for some failures 52 53 Unpacking non-sequence 54 55 >>> a, b, c = 7 56 Traceback (most recent call last): 57 ... 58 TypeError: 'int' object is not iterable 59 60 Unpacking tuple of wrong size 61 62 >>> a, b = t 63 Traceback (most recent call last): 64 ... 65 ValueError: too many values to unpack 66 67 Unpacking tuple of wrong size 68 69 >>> a, b = l 70 Traceback (most recent call last): 71 ... 72 ValueError: too many values to unpack 73 74 Unpacking sequence too short 75 76 >>> a, b, c, d = Seq() 77 Traceback (most recent call last): 78 ... 79 ValueError: need more than 3 values to unpack 80 81 Unpacking sequence too long 82 83 >>> a, b = Seq() 84 Traceback (most recent call last): 85 ... 86 ValueError: too many values to unpack 87 88 Unpacking a sequence where the test for too long raises a different kind of 89 error 90 91 >>> class BozoError(Exception): 92 ... pass 93 ... 94 >>> class BadSeq: 95 ... def __getitem__(self, i): 96 ... if i >= 0 and i < 3: 97 ... return i 98 ... elif i == 3: 99 ... raise BozoError 100 ... else: 101 ... raise IndexError 102 ... 103 104 Trigger code while not expecting an IndexError (unpack sequence too long, wrong 105 error) 106 107 >>> a, b, c, d, e = BadSeq() 108 Traceback (most recent call last): 109 ... 110 BozoError 111 112 Trigger code while expecting an IndexError (unpack sequence too short, wrong 113 error) 114 115 >>> a, b, c = BadSeq() 116 Traceback (most recent call last): 117 ... 118 BozoError 119 120 """ 121 122 __test__ = {'doctests' : doctests} 123 124 def test_main(verbose=False): 125 from test import test_support 126 from test import test_unpack 127 test_support.run_doctest(test_unpack, verbose) 128 129 if __name__ == "__main__": 130 test_main(verbose=True) 131
