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namedtuple: add defaults to the Python 3.6 syntax #338

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Merged
merged 2 commits into from
Jan 18, 2017
Merged

namedtuple: add defaults to the Python 3.6 syntax #338

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8b3eabd
namedtuple: add defaults to the Python 3.6 syntax
JelleZijlstra Dec 2, 2016
dab3093
namedtuple with defaults: improve error message and remove redundant …
JelleZijlstra Dec 3, 2016
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26 changes: 26 additions & 0 deletions src/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1376,6 +1376,10 @@ class G(Generic[T]):
class CoolEmployee(NamedTuple):
name: str
cool: int

class CoolEmployeeWithDefault(NamedTuple):
name: str
cool: int = 0
"""

if PY36:
Expand Down Expand Up @@ -1920,6 +1924,28 @@ def test_annotation_usage(self):
self.assertEqual(CoolEmployee._fields, ('name', 'cool'))
self.assertEqual(CoolEmployee._field_types, dict(name=str, cool=int))

@skipUnless(PY36, 'Python 3.6 required')
def test_annotation_usage_with_default(self):
jelle = CoolEmployeeWithDefault('Jelle')
self.assertIsInstance(jelle, CoolEmployeeWithDefault)
self.assertIsInstance(jelle, tuple)
self.assertEqual(jelle.name, 'Jelle')
self.assertEqual(jelle.cool, 0)
cooler_employee = CoolEmployeeWithDefault('Sjoerd', 1)
self.assertEqual(cooler_employee.cool, 1)

self.assertEqual(CoolEmployeeWithDefault.__name__, 'CoolEmployeeWithDefault')
self.assertEqual(CoolEmployeeWithDefault._fields, ('name', 'cool'))
self.assertEqual(CoolEmployeeWithDefault._field_types, dict(name=str, cool=int))
self.assertEqual(CoolEmployeeWithDefault._field_defaults, dict(cool=0))

with self.assertRaises(TypeError):
exec("""
class NonDefaultAfterDefault(NamedTuple):
x: int = 3
y: int
""")

@skipUnless(PY36, 'Python 3.6 required')
def test_namedtuple_keyword_usage(self):
LocalEmployee = NamedTuple("LocalEmployee", name=str, age=int)
Expand Down
17 changes: 16 additions & 1 deletion src/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1916,7 +1916,22 @@ def __new__(cls, typename, bases, ns):
raise TypeError("Class syntax for NamedTuple is only supported"
" in Python 3.6+")
types = ns.get('__annotations__', {})
return _make_nmtuple(typename, types.items())
nm_tpl = _make_nmtuple(typename, types.items())
defaults = []
defaults_dict = {}
for field_name in types:
if field_name in ns:
default_value = ns[field_name]
defaults.append(default_value)
defaults_dict[field_name] = default_value
elif defaults:
raise TypeError("Non-default namedtuple field {field_name} cannot follow default"
" field(s) {default_names}"
.format(field_name=field_name,
default_names=', '.join(defaults_dict.keys())))
nm_tpl.__new__.__defaults__ = tuple(defaults)
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Also probably you could use only defaults_dict and then write here = tuple(defaults_dict.values()), since dict is ordered in Python 3.6.

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As I understand it, dict ordering is an implementation detail of CPython 3.6 and a conforming Python 3.6 implementation could choose to not implement ordering, so this code shouldn't rely on dict ordering (except for class namespaces and **kwargs because of PEP 520 and PEP 468).

nm_tpl._field_defaults = defaults_dict
return nm_tpl

class NamedTuple(metaclass=NamedTupleMeta):
"""Typed version of namedtuple.
Expand Down