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madman-bob
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bpo-32321: Add pure Python fallback for functools.reduce (GH-8548)
1 parent 6279c1c commit e25d5fc

3 files changed

Lines changed: 80 additions & 36 deletions

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‎Lib/functools.py‎

Lines changed: 39 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -13,10 +13,6 @@
1313
'total_ordering', 'cmp_to_key', 'lru_cache', 'reduce', 'partial',
1414
'partialmethod', 'singledispatch', 'singledispatchmethod']
1515

16-
try:
17-
from _functools import reduce
18-
except ImportError:
19-
pass
2016
from abc import get_cache_token
2117
from collections import namedtuple
2218
# import types, weakref # Deferred to single_dispatch()
@@ -226,6 +222,45 @@ def __ge__(self, other):
226222
pass
227223

228224

225+
################################################################################
226+
### reduce() sequence to a single item
227+
################################################################################
228+
229+
_initial_missing = object()
230+
231+
def reduce(function, sequence, initial=_initial_missing):
232+
"""
233+
reduce(function, sequence[, initial]) -> value
234+
235+
Apply a function of two arguments cumulatively to the items of a sequence,
236+
from left to right, so as to reduce the sequence to a single value.
237+
For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
238+
((((1+2)+3)+4)+5). If initial is present, it is placed before the items
239+
of the sequence in the calculation, and serves as a default when the
240+
sequence is empty.
241+
"""
242+
243+
it = iter(sequence)
244+
245+
if initial is _initial_missing:
246+
try:
247+
value = next(it)
248+
except StopIteration:
249+
raise TypeError("reduce() of empty sequence with no initial value") from None
250+
else:
251+
value = initial
252+
253+
for element in it:
254+
value = function(value, element)
255+
256+
return value
257+
258+
try:
259+
from _functools import reduce
260+
except ImportError:
261+
pass
262+
263+
229264
################################################################################
230265
### partial() argument application
231266
################################################################################

‎Lib/test/test_functools.py‎

Lines changed: 39 additions & 32 deletions
Original file line numberDiff line numberDiff line change
@@ -746,11 +746,8 @@ def wrapper():
746746
self.assertEqual(wrapper.attr, 'This is a different test')
747747
self.assertEqual(wrapper.dict_attr, f.dict_attr)
748748

749-
@unittest.skipUnless(c_functools, 'requires the C _functools module')
750-
class TestReduce(unittest.TestCase):
751-
if c_functools:
752-
func = c_functools.reduce
753749

750+
class TestReduce:
754751
def test_reduce(self):
755752
class Squares:
756753
def __init__(self, max):
@@ -769,42 +766,42 @@ def __getitem__(self, i):
769766
return self.sofar[i]
770767
def add(x, y):
771768
return x + y
772-
self.assertEqual(self.func(add, ['a', 'b', 'c'], ''), 'abc')
769+
self.assertEqual(self.reduce(add, ['a', 'b', 'c'], ''), 'abc')
773770
self.assertEqual(
774-
self.func(add, [['a', 'c'], [], ['d', 'w']], []),
771+
self.reduce(add, [['a', 'c'], [], ['d', 'w']], []),
775772
['a','c','d','w']
776773
)
777-
self.assertEqual(self.func(lambda x, y: x*y, range(2,8), 1), 5040)
774+
self.assertEqual(self.reduce(lambda x, y: x*y, range(2,8), 1), 5040)
778775
self.assertEqual(
779-
self.func(lambda x, y: x*y, range(2,21), 1),
776+
self.reduce(lambda x, y: x*y, range(2,21), 1),
780777
2432902008176640000
781778
)
782-
self.assertEqual(self.func(add, Squares(10)), 285)
783-
self.assertEqual(self.func(add, Squares(10), 0), 285)
784-
self.assertEqual(self.func(add, Squares(0), 0), 0)
785-
self.assertRaises(TypeError, self.func)
786-
self.assertRaises(TypeError, self.func, 42, 42)
787-
self.assertRaises(TypeError, self.func, 42, 42, 42)
788-
self.assertEqual(self.func(42, "1"), "1") # func is never called with one item
789-
self.assertEqual(self.func(42, "", "1"), "1") # func is never called with one item
790-
self.assertRaises(TypeError, self.func, 42, (42, 42))
791-
self.assertRaises(TypeError, self.func, add, []) # arg 2 must not be empty sequence with no initial value
792-
self.assertRaises(TypeError, self.func, add, "")
793-
self.assertRaises(TypeError, self.func, add, ())
794-
self.assertRaises(TypeError, self.func, add, object())
779+
self.assertEqual(self.reduce(add, Squares(10)), 285)
780+
self.assertEqual(self.reduce(add, Squares(10), 0), 285)
781+
self.assertEqual(self.reduce(add, Squares(0), 0), 0)
782+
self.assertRaises(TypeError, self.reduce)
783+
self.assertRaises(TypeError, self.reduce, 42, 42)
784+
self.assertRaises(TypeError, self.reduce, 42, 42, 42)
785+
self.assertEqual(self.reduce(42, "1"), "1") # func is never called with one item
786+
self.assertEqual(self.reduce(42, "", "1"), "1") # func is never called with one item
787+
self.assertRaises(TypeError, self.reduce, 42, (42, 42))
788+
self.assertRaises(TypeError, self.reduce, add, []) # arg 2 must not be empty sequence with no initial value
789+
self.assertRaises(TypeError, self.reduce, add, "")
790+
self.assertRaises(TypeError, self.reduce, add, ())
791+
self.assertRaises(TypeError, self.reduce, add, object())
795792

796793
class TestFailingIter:
797794
def __iter__(self):
798795
raise RuntimeError
799-
self.assertRaises(RuntimeError, self.func, add, TestFailingIter())
796+
self.assertRaises(RuntimeError, self.reduce, add, TestFailingIter())
800797

801-
self.assertEqual(self.func(add, [], None), None)
802-
self.assertEqual(self.func(add, [], 42), 42)
798+
self.assertEqual(self.reduce(add, [], None), None)
799+
self.assertEqual(self.reduce(add, [], 42), 42)
803800

804801
class BadSeq:
805802
def __getitem__(self, index):
806803
raise ValueError
807-
self.assertRaises(ValueError, self.func, 42, BadSeq())
804+
self.assertRaises(ValueError, self.reduce, 42, BadSeq())
808805

809806
# Test reduce()'s use of iterators.
810807
def test_iterator_usage(self):
@@ -818,15 +815,25 @@ def __getitem__(self, i):
818815
raise IndexError
819816

820817
from operator import add
821-
self.assertEqual(self.func(add, SequenceClass(5)), 10)
822-
self.assertEqual(self.func(add, SequenceClass(5), 42), 52)
823-
self.assertRaises(TypeError, self.func, add, SequenceClass(0))
824-
self.assertEqual(self.func(add, SequenceClass(0), 42), 42)
825-
self.assertEqual(self.func(add, SequenceClass(1)), 0)
826-
self.assertEqual(self.func(add, SequenceClass(1), 42), 42)
818+
self.assertEqual(self.reduce(add, SequenceClass(5)), 10)
819+
self.assertEqual(self.reduce(add, SequenceClass(5), 42), 52)
820+
self.assertRaises(TypeError, self.reduce, add, SequenceClass(0))
821+
self.assertEqual(self.reduce(add, SequenceClass(0), 42), 42)
822+
self.assertEqual(self.reduce(add, SequenceClass(1)), 0)
823+
self.assertEqual(self.reduce(add, SequenceClass(1), 42), 42)
827824

828825
d = {"one": 1, "two": 2, "three": 3}
829-
self.assertEqual(self.func(add, d), "".join(d.keys()))
826+
self.assertEqual(self.reduce(add, d), "".join(d.keys()))
827+
828+
829+
@unittest.skipUnless(c_functools, 'requires the C _functools module')
830+
class TestReduceC(TestReduce, unittest.TestCase):
831+
if c_functools:
832+
reduce = c_functools.reduce
833+
834+
835+
class TestReducePy(TestReduce, unittest.TestCase):
836+
reduce = staticmethod(py_functools.reduce)
830837

831838

832839
class TestCmpToKey:

‎Misc/NEWS.d/next/Library/2018-07-29-13-50-32.bpo-32321.hDoNKC.rst‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
Add pure Python fallback for functools.reduce.
2+
Patch by Robert Wright.

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