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Use identity ('is') comparison for no_default sentinel in itertoolz #625

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Use identity ('is') comparison for no_default sentinel in itertoolz #625

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22 changes: 11 additions & 11 deletions toolz/itertoolz.py
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Original file line number Diff line number Diff line change
Expand Up @@ -55,7 +55,7 @@ def accumulate(binop, seq, initial=no_default):
itertools.accumulate : In standard itertools for Python 3.2+
"""
seq = iter(seq)
if initial == no_default:
if initial is no_default:
try:
result = next(seq)
except StopIteration:
Expand Down Expand Up @@ -448,7 +448,7 @@ def get(ind, seq, default=no_default):
return seq[ind]
except TypeError: # `ind` may be a list
if isinstance(ind, list):
if default == no_default:
if default is no_default:
if len(ind) > 1:
return operator.itemgetter(*ind)(seq)
elif ind:
Expand All @@ -457,12 +457,12 @@ def get(ind, seq, default=no_default):
return ()
else:
return tuple(_get(i, seq, default) for i in ind)
elif default != no_default:
elif default is not no_default:
return default
else:
raise
except (KeyError, IndexError): # we know `ind` is not a list
if default == no_default:
if default is no_default:
raise
else:
return default
Expand Down Expand Up @@ -605,7 +605,7 @@ def reduceby(key, binop, seq, init=no_default):
{True: set([2, 4]),
False: set([1, 3])}
"""
is_no_default = init == no_default
is_no_default = init is no_default
if not is_no_default and not callable(init):
_init = init
init = lambda: _init
Expand Down Expand Up @@ -787,7 +787,7 @@ def pluck(ind, seqs, default=no_default):
get
map
"""
if default == no_default:
if default is no_default:
get = getter(ind)
return map(get, seqs)
elif isinstance(ind, list):
Expand Down Expand Up @@ -876,14 +876,14 @@ def join(leftkey, leftseq, rightkey, rightseq,

d = groupby(leftkey, leftseq)

if left_default == no_default and right_default == no_default:
if left_default is no_default and right_default is no_default:
# Inner Join
for item in rightseq:
key = rightkey(item)
if key in d:
for left_match in d[key]:
yield (left_match, item)
elif left_default != no_default and right_default == no_default:
elif left_default is not no_default and right_default is no_default:
# Right Join
for item in rightseq:
key = rightkey(item)
Expand All @@ -892,11 +892,11 @@ def join(leftkey, leftseq, rightkey, rightseq,
yield (left_match, item)
else:
yield (left_default, item)
elif right_default != no_default:
elif right_default is not no_default:
seen_keys = set()
seen = seen_keys.add

if left_default == no_default:
if left_default is no_default:
# Left Join
for item in rightseq:
key = rightkey(item)
Expand Down Expand Up @@ -945,7 +945,7 @@ def diff(*seqs, **kwargs):
if N < 2:
raise TypeError('Too few sequences given (min 2 required)')
default = kwargs.get('default', no_default)
if default == no_default:
if default is no_default:
iters = zip(*seqs)
else:
iters = zip_longest(*seqs, fillvalue=default)
Expand Down
41 changes: 31 additions & 10 deletions toolz/tests/test_itertoolz.py
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,8 @@
from operator import add, mul


# is comparison will fail between this and no_default
# A string equal to (but not identical to) the no_default sentinel.
# Identity-based ('is') comparisons correctly treat this as a real value.
no_default2 = loads(dumps('__no__default__'))


Expand Down Expand Up @@ -217,7 +218,9 @@ def test_get():
assert raises(KeyError, lambda: get(10, {'a': 1}))
assert raises(TypeError, lambda: get({}, [1, 2, 3]))
assert raises(TypeError, lambda: get([1, 2, 3], 1, None))
assert raises(KeyError, lambda: get('foo', {}, default=no_default2))
# no_default2 is equal to but not identical to the sentinel, so it is used
# as a real default value (identity comparison means no false collision).
assert get('foo', {}, default=no_default2) == no_default2


def test_mapcat():
Expand Down Expand Up @@ -285,8 +288,11 @@ def test_reduceby():

def test_reduce_by_init():
assert reduceby(iseven, add, [1, 2, 3, 4]) == {True: 2 + 4, False: 1 + 3}
assert reduceby(iseven, add, [1, 2, 3, 4], no_default2) == {True: 2 + 4,
False: 1 + 3}
# no_default2 is a real value (not the sentinel), so it is used as the
# literal init; confirm it is passed through, not silently ignored.
assert reduceby(iseven, lambda acc, x: acc, [1, 2, 3, 4], no_default2) == {
True: no_default2, False: no_default2
}


def test_reduce_by_callable_default():
Expand Down Expand Up @@ -314,7 +320,11 @@ def binop(a, b):
start = object()
assert list(accumulate(binop, [], start)) == [start]
assert list(accumulate(binop, [])) == []
assert list(accumulate(add, [1, 2, 3], no_default2)) == [1, 3, 6]
# no_default2 is a real value (not the sentinel), so accumulate uses it as
# the actual initial value; confirm it appears first in the output.
assert list(accumulate(lambda a, b: b, [1, 2, 3], no_default2)) == [
no_default2, 1, 2, 3
]


def test_accumulate_works_on_consumable_iterables():
Expand Down Expand Up @@ -394,8 +404,10 @@ def test_pluck():
assert raises(IndexError, lambda: list(pluck(1, [[0]])))
assert raises(KeyError, lambda: list(pluck('name', [{'id': 1}])))

# no_default2 is a real value (not the sentinel), so it is used as the
# fallback for missing items rather than triggering "no default" semantics.
assert list(pluck(0, [[0, 1], [2, 3], [4, 5]], no_default2)) == [0, 2, 4]
assert raises(IndexError, lambda: list(pluck(1, [[0]], no_default2)))
assert list(pluck(1, [[0]], no_default2)) == [no_default2]


def test_join():
Expand All @@ -414,10 +426,19 @@ def addpair(pair):

assert result == expected

result = set(starmap(add, join(first, names, second, fruit,
left_default=no_default2,
right_default=no_default2)))
assert result == expected
# no_default2 is a real value (not the sentinel), so passing it as
# left_default/right_default activates outer-join semantics.
# Items with key 3 in names have no match in fruit → paired with no_default2.
result_outer = list(join(first, names, second, fruit,
left_default=no_default2,
right_default=no_default2))
matched = {pair for pair in result_outer if pair[0] != no_default2 and pair[1] != no_default2}
assert matched == {((1, 'one'), ('apple', 1)),
((1, 'one'), ('orange', 1)),
((2, 'two'), ('banana', 2)),
((2, 'two'), ('coconut', 2))}
# Unmatched left item (3, 'three') should appear paired with no_default2
assert ((3, 'three'), no_default2) in result_outer


def test_getter():
Expand Down