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import collections
import itertools
import sys
import timeit
import unittest
from typing import Callable, Iterable, Tuple
def oddity(iterable: Iterable,
key: Callable[[object], object]=None,
first: bool=False) -> Tuple[object, object]:
"""Find the element that is different.
Any iterable. Can be an infinite sequence *if* ``first`` is
specified *and* there is a common item *and* at least one
different item.
A function used to extract a comparison key from each
element; if not provided, the elements themselves are
Return early when the first uncommon item is found. This can
be *much* faster when the uncommon item is near the front of
the iterable, but it also adds a bit of overhead. The items
won't be validated when using this, but it will work with
infinite sequences.
The key of the common element
The different element or ``None`` if all the elements are
The sequence is empty.
2 or more distinct elements are found (determined by their
keys). The string ``'123'`` will trigger this error.
Multiple common elements are found. The string ``'11222``
will trigger this error.
No common element is found. The string ``'12'`` will trigger
this error.
seen = []
common = []
uncommon = []
for item in iter(iterable):
item_key = key(item) if key else item
if item_key in seen:
if item_key in common:
if first and uncommon:
return item_key, uncommon[1]
if len(common) == 2:
raise TooManyCommonValuesError
if item_key in uncommon:
i = uncommon.index(item_key)
j = i + 2
uncommon[i:j] = []
if len(seen) == 3:
raise TooManyDistinctValuesError
uncommon.extend((item_key, item))
if len(seen) == 0:
raise EmptyError
if len(common) == 0:
raise NoCommonValueError
if len(uncommon) == 0:
# All values are the same
uncommon_value = None
uncommon_value = uncommon[1]
return common[0], uncommon_value
def oddity_groupby(items, key=None, _sentinel=object()):
sorted_items = sorted(items, key=key)
grouped_items = itertools.groupby(sorted_items, key=key)
a_key, a_group = next(grouped_items, (None, None))
if a_group is None:
raise EmptyError
a1 = next(a_group, _sentinel)
a2 = next(a_group, _sentinel)
b_key, b_group = next(grouped_items, (None, None))
if b_group is None:
return a_key, None
b1 = next(b_group, _sentinel)
b2 = next(b_group, _sentinel)
c = next(grouped_items, None)
if c is not None:
raise TooManyDistinctValuesError
if a2 is _sentinel:
if b2 is _sentinel:
raise NoCommonValueError
return b_key, a1
if b2 is _sentinel:
if a2 is _sentinel:
raise NoCommonValueError
return a_key, b1
raise TooManyCommonValuesError
def oddity_nb(iterable, key=None):
summary = collections.defaultdict(list)
for element in iterable:
k = key(element) if key is not None else element
if len(summary) == 1:
k, _ = summary.popitem()
return k, None
elif len(summary) == 2:
common, different = list(summary.items())
if len(common[1]) == 1:
common, different = different, common
return common[0], different[1][0]
raise ValueError("Wrong number of distinct values")
class EmptyError(ValueError):
class TooManyDistinctValuesError(ValueError):
class TooManyCommonValuesError(ValueError):
class NoCommonValueError(ValueError):
class Tests(unittest.TestCase):
def test_list(self):
key, diff = oddity([1, 2, 1, 1])
self.assertEqual(diff, 2)
def test_list_empty(self):
self.assertRaises(EmptyError, oddity, [])
def test_list_all_the_same(self):
key, diff = oddity([1, 1, 1, 1])
self.assertEqual((key, diff), (1, None))
def test_list_too_many_distinct(self):
self.assertRaises(TooManyDistinctValuesError, oddity, [1, 2, 3])
def test_list_too_many_common(self):
self.assertRaises(TooManyCommonValuesError, oddity, [2, 1, 2, 1, 1])
def test_str(self):
key, diff = oddity('aaaaba')
self.assertEqual((key, diff), ('a', 'b'))
def test_str_empty(self):
self.assertRaises(EmptyError, oddity, '')
def test_str_all_the_same(self):
key, diff = oddity('aaaaaa')
self.assertEqual((key, diff), ('a', None))
def test_str_too_many_distinct(self):
self.assertRaises(TooManyDistinctValuesError, oddity, 'aaaaaabc')
def test_with_key(self):
items = [10, 11, 12, 23, 14, 10]
key, diff = oddity(items, key=lambda v: v // 10)
self.assertEqual((key, diff), (1, 23))
def test_one_of_each(self):
self.assertRaises(NoCommonValueError, oddity, 'ab')
def test_two_of_each(self):
self.assertRaises(TooManyCommonValuesError, oddity, 'abab')
if __name__ == '__main__':
if len(sys.argv) == 2:
s = ['1'] * 100
s[-1] = '0'
print(timeit.timeit('oddity(s)', number=100000, globals=globals()))
print(timeit.timeit('oddity_groupby(s)', number=100000, globals=globals()))
print(timeit.timeit('oddity_nb(s)', number=100000, globals=globals()))
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