Mercurial > cpython-lru_cache-weakref

annotate Lib/test/test_iterlen.py @ 79675:c0a2294de787 2.7

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Issue #16199: Backport 2to3 typo fix from 3.2.
author Chris Jerdonek <chris.jerdonek@gmail.com>
date Thu, 11 Oct 2012 16:15:46 -0700
parents cd8d3c2d3bce
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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1 """ Test Iterator Length Transparency
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2
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3 Some functions or methods which accept general iterable arguments have
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4 optional, more efficient code paths if they know how many items to expect.
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5 For instance, map(func, iterable), will pre-allocate the exact amount of
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6 space required whenever the iterable can report its length.
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7
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8 The desired invariant is: len(it)==len(list(it)).
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9
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10 A complication is that an iterable and iterator can be the same object. To
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11 maintain the invariant, an iterator needs to dynamically update its length.
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12 For instance, an iterable such as xrange(10) always reports its length as ten,
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13 but it=iter(xrange(10)) starts at ten, and then goes to nine after it.next().
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14 Having this capability means that map() can ignore the distinction between
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15 map(func, iterable) and map(func, iter(iterable)).
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16
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17 When the iterable is immutable, the implementation can straight-forwardly
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18 report the original length minus the cumulative number of calls to next().
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19 This is the case for tuples, xrange objects, and itertools.repeat().
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20
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21 Some containers become temporarily immutable during iteration. This includes
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22 dicts, sets, and collections.deque. Their implementation is equally simple
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23 though they need to permanently set their length to zero whenever there is
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24 an attempt to iterate after a length mutation.
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25
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26 The situation slightly more involved whenever an object allows length mutation
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27 during iteration. Lists and sequence iterators are dynamically updatable.
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28 So, if a list is extended during iteration, the iterator will continue through
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29 the new items. If it shrinks to a point before the most recent iteration,
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30 then no further items are available and the length is reported at zero.
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31
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32 Reversed objects can also be wrapped around mutable objects; however, any
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33 appends after the current position are ignored. Any other approach leads
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34 to confusion and possibly returning the same item more than once.
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35
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36 The iterators not listed above, such as enumerate and the other itertools,
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37 are not length transparent because they have no way to distinguish between
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38 iterables that report static length and iterators whose length changes with
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39 each call (i.e. the difference between enumerate('abc') and
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40 enumerate(iter('abc')).
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41
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42 """
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43
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44 import unittest
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45 from test import test_support
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46 from itertools import repeat
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47 from collections import deque
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48 from __builtin__ import len as _len
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49
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50 n = 10
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51
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52 def len(obj):
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53 try:
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54 return _len(obj)
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55 except TypeError:
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56 try:
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57 # note: this is an internal undocumented API,
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58 # don't rely on it in your own programs
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59 return obj.__length_hint__()
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60 except AttributeError:
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61 raise TypeError
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62
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63 class TestInvariantWithoutMutations(unittest.TestCase):
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64
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65 def test_invariant(self):
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66 it = self.it
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67 for i in reversed(xrange(1, n+1)):
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68 self.assertEqual(len(it), i)
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69 it.next()
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70 self.assertEqual(len(it), 0)
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71 self.assertRaises(StopIteration, it.next)
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72 self.assertEqual(len(it), 0)
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73
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74 class TestTemporarilyImmutable(TestInvariantWithoutMutations):
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75
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76 def test_immutable_during_iteration(self):
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77 # objects such as deques, sets, and dictionaries enforce
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78 # length immutability during iteration
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79
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80 it = self.it
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81 self.assertEqual(len(it), n)
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82 it.next()
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83 self.assertEqual(len(it), n-1)
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84 self.mutate()
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85 self.assertRaises(RuntimeError, it.next)
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86 self.assertEqual(len(it), 0)
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87
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88 ## ------- Concrete Type Tests -------
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89
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90 class TestRepeat(TestInvariantWithoutMutations):
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91
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92 def setUp(self):
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93 self.it = repeat(None, n)
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94
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95 def test_no_len_for_infinite_repeat(self):
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96 # The repeat() object can also be infinite
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97 self.assertRaises(TypeError, len, repeat(None))
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98
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99 class TestXrange(TestInvariantWithoutMutations):
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100
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101 def setUp(self):
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102 self.it = iter(xrange(n))
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103
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104 class TestXrangeCustomReversed(TestInvariantWithoutMutations):
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105
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106 def setUp(self):
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107 self.it = reversed(xrange(n))
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108
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109 class TestTuple(TestInvariantWithoutMutations):
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110
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111 def setUp(self):
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112 self.it = iter(tuple(xrange(n)))
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113
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114 ## ------- Types that should not be mutated during iteration -------
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115
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116 class TestDeque(TestTemporarilyImmutable):
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117
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118 def setUp(self):
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119 d = deque(xrange(n))
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120 self.it = iter(d)
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121 self.mutate = d.pop
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122
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123 class TestDequeReversed(TestTemporarilyImmutable):
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124
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125 def setUp(self):
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126 d = deque(xrange(n))
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127 self.it = reversed(d)
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128 self.mutate = d.pop
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129
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130 class TestDictKeys(TestTemporarilyImmutable):
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131
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132 def setUp(self):
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133 d = dict.fromkeys(xrange(n))
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134 self.it = iter(d)
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135 self.mutate = d.popitem
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136
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137 class TestDictItems(TestTemporarilyImmutable):
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138
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139 def setUp(self):
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140 d = dict.fromkeys(xrange(n))
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141 self.it = d.iteritems()
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142 self.mutate = d.popitem
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143
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144 class TestDictValues(TestTemporarilyImmutable):
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145
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146 def setUp(self):
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147 d = dict.fromkeys(xrange(n))
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148 self.it = d.itervalues()
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149 self.mutate = d.popitem
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150
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151 class TestSet(TestTemporarilyImmutable):
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152
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153 def setUp(self):
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154 d = set(xrange(n))
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155 self.it = iter(d)
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156 self.mutate = d.pop
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157
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158 ## ------- Types that can mutate during iteration -------
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159
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160 class TestList(TestInvariantWithoutMutations):
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161
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162 def setUp(self):
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163 self.it = iter(range(n))
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164
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165 def test_mutation(self):
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166 d = range(n)
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167 it = iter(d)
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168 it.next()
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169 it.next()
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170 self.assertEqual(len(it), n-2)
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171 d.append(n)
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172 self.assertEqual(len(it), n-1) # grow with append
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173 d[1:] = []
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174 self.assertEqual(len(it), 0)
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175 self.assertEqual(list(it), [])
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176 d.extend(xrange(20))
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177 self.assertEqual(len(it), 0)
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178
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179 class TestListReversed(TestInvariantWithoutMutations):
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180
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181 def setUp(self):
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182 self.it = reversed(range(n))
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183
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184 def test_mutation(self):
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185 d = range(n)
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186 it = reversed(d)
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187 it.next()
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188 it.next()
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189 self.assertEqual(len(it), n-2)
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190 d.append(n)
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191 self.assertEqual(len(it), n-2) # ignore append
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192 d[1:] = []
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193 self.assertEqual(len(it), 0)
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194 self.assertEqual(list(it), []) # confirm invariant
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195 d.extend(xrange(20))
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196 self.assertEqual(len(it), 0)
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197
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198 ## -- Check to make sure exceptions are not suppressed by __length_hint__()
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199
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200
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201 class BadLen(object):
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202 def __iter__(self): return iter(range(10))
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203 def __len__(self):
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204 raise RuntimeError('hello')
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205
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206 class BadLengthHint(object):
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207 def __iter__(self): return iter(range(10))
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208 def __length_hint__(self):
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209 raise RuntimeError('hello')
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210
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211 class NoneLengthHint(object):
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212 def __iter__(self): return iter(range(10))
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213 def __length_hint__(self):
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214 return None
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215
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216 class TestLengthHintExceptions(unittest.TestCase):
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217
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218 def test_issue1242657(self):
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219 self.assertRaises(RuntimeError, list, BadLen())
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220 self.assertRaises(RuntimeError, list, BadLengthHint())
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221 self.assertRaises(RuntimeError, [].extend, BadLen())
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222 self.assertRaises(RuntimeError, [].extend, BadLengthHint())
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223 self.assertRaises(RuntimeError, zip, BadLen())
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224 self.assertRaises(RuntimeError, zip, BadLengthHint())
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225 self.assertRaises(RuntimeError, filter, None, BadLen())
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226 self.assertRaises(RuntimeError, filter, None, BadLengthHint())
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227 self.assertRaises(RuntimeError, map, chr, BadLen())
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228 self.assertRaises(RuntimeError, map, chr, BadLengthHint())
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229 b = bytearray(range(10))
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230 self.assertRaises(RuntimeError, b.extend, BadLen())
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231 self.assertRaises(RuntimeError, b.extend, BadLengthHint())
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232
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233 def test_invalid_hint(self):
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234 # Make sure an invalid result doesn't muck-up the works
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235 self.assertEqual(list(NoneLengthHint()), list(range(10)))
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236
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237
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238 def test_main():
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239 unittests = [
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240 TestRepeat,
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241 TestXrange,
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242 TestXrangeCustomReversed,
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243 TestTuple,
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244 TestDeque,
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245 TestDequeReversed,
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246 TestDictKeys,
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247 TestDictItems,
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248 TestDictValues,
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249 TestSet,
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250 TestList,
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251 TestListReversed,
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252 TestLengthHintExceptions,
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253 ]
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254 test_support.run_unittest(*unittests)
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255
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256 if __name__ == "__main__":
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257 test_main()