Treat typing.NamedTuple self as a sequence (#5346)

* Treat `typing.NamedTuple` self as a sequence

Closes #5312

* Support emmitting `unbalanced-tuple-unpacking` with `typing.NamedTuple`

* Add typehint and default to `None`

* Use Marc's suggested improvements

Author: mbyrnepr2

ChangeLog

@@ -18,6 +18,10 @@ Release date: TBA
 
   Closes #4716
 
+* Fix false positive - Allow unpacking of ``self`` in a subclass of ``typing.NamedTuple``.
+
+  Closes #5312
+
 * Fix false negative for ``consider-iterating-dictionary`` during membership checks encapsulated in iterables
   or ``not in`` checks
 

pylint/checkers/variables.py

@@ -2130,9 +2130,17 @@ def _check_unpacking(self, inferred, node, targets):
         ):
             # Variable-length argument, we can't determine the length.
             return
+
+        # Attempt to check unpacking is properly balanced
+        values: Optional[List] = None
         if isinstance(inferred, (nodes.Tuple, nodes.List)):
-            # attempt to check unpacking is properly balanced
             values = inferred.itered()
+        elif isinstance(inferred, astroid.Instance) and any(
+            ancestor.qname() == "typing.NamedTuple" for ancestor in inferred.ancestors()
+        ):
+            values = [i for i in inferred.values() if isinstance(i, nodes.AssignName)]
+
+        if values:
             if len(targets) != len(values):
                 # Check if we have starred nodes.
                 if any(isinstance(target, nodes.Starred) for target in targets):

tests/functional/u/unbalanced_tuple_unpacking.py

@@ -1,8 +1,9 @@
 """Check possible unbalanced tuple unpacking """
 from __future__ import absolute_import
+from typing import NamedTuple
 from functional.u.unpacking import unpack
 
-# pylint: disable=using-constant-test, useless-object-inheritance,import-outside-toplevel
+# pylint: disable=missing-class-docstring, missing-function-docstring, using-constant-test, useless-object-inheritance,import-outside-toplevel
 
 def do_stuff():
     """This is not right."""
@@ -106,3 +107,24 @@ def test_issue_559():
     from ctypes import c_int
     root_x, root_y, win_x, win_y = [c_int()] * 4
     return root_x, root_y, win_x, win_y
+
+
+class MyClass(NamedTuple):
+    first: float
+    second: float
+    third: float = 1.0
+
+    def my_sum(self):
+        """Unpack 3 variables"""
+        first, second, third = self
+        return first + second + third
+
+    def sum_unpack_3_into_4(self):
+        """Attempt to unpack 3 variables into 4"""
+        first, second, third, fourth = self # [unbalanced-tuple-unpacking]
+        return first + second + third + fourth
+
+    def sum_unpack_3_into_2(self):
+        """Attempt to unpack 3 variables into 2"""
+        first, second = self # [unbalanced-tuple-unpacking]
+        return first + second

tests/functional/u/unbalanced_tuple_unpacking.txt

@@ -1,5 +1,7 @@
-unbalanced-tuple-unpacking:9:4:9:27:do_stuff:"Possible unbalanced tuple unpacking with sequence (1, 2, 3): left side has 2 label(s), right side has 3 value(s)":UNDEFINED
-unbalanced-tuple-unpacking:14:4:14:29:do_stuff1:"Possible unbalanced tuple unpacking with sequence [1, 2, 3]: left side has 2 label(s), right side has 3 value(s)":UNDEFINED
-unbalanced-tuple-unpacking:19:4:19:29:do_stuff2:"Possible unbalanced tuple unpacking with sequence (1, 2, 3): left side has 2 label(s), right side has 3 value(s)":UNDEFINED
-unbalanced-tuple-unpacking:69:4:69:28:do_stuff9:"Possible unbalanced tuple unpacking with sequence defined at line 7 of functional.u.unpacking: left side has 2 label(s), right side has 3 value(s)":UNDEFINED
-unbalanced-tuple-unpacking:81:8:81:33:UnbalancedUnpacking.test:"Possible unbalanced tuple unpacking with sequence defined at line 7 of functional.u.unpacking: left side has 2 label(s), right side has 3 value(s)":UNDEFINED
+unbalanced-tuple-unpacking:10:4:10:27:do_stuff:"Possible unbalanced tuple unpacking with sequence (1, 2, 3): left side has 2 label(s), right side has 3 value(s)":UNDEFINED
+unbalanced-tuple-unpacking:15:4:15:29:do_stuff1:"Possible unbalanced tuple unpacking with sequence [1, 2, 3]: left side has 2 label(s), right side has 3 value(s)":UNDEFINED
+unbalanced-tuple-unpacking:20:4:20:29:do_stuff2:"Possible unbalanced tuple unpacking with sequence (1, 2, 3): left side has 2 label(s), right side has 3 value(s)":UNDEFINED
+unbalanced-tuple-unpacking:70:4:70:28:do_stuff9:"Possible unbalanced tuple unpacking with sequence defined at line 7 of functional.u.unpacking: left side has 2 label(s), right side has 3 value(s)":UNDEFINED
+unbalanced-tuple-unpacking:82:8:82:33:UnbalancedUnpacking.test:"Possible unbalanced tuple unpacking with sequence defined at line 7 of functional.u.unpacking: left side has 2 label(s), right side has 3 value(s)":UNDEFINED
+unbalanced-tuple-unpacking:124:8:124:43:MyClass.sum_unpack_3_into_4:"Possible unbalanced tuple unpacking with sequence defined at line 112: left side has 4 label(s), right side has 3 value(s)":UNDEFINED
+unbalanced-tuple-unpacking:129:8:129:28:MyClass.sum_unpack_3_into_2:"Possible unbalanced tuple unpacking with sequence defined at line 112: left side has 2 label(s), right side has 3 value(s)":UNDEFINED

tests/functional/u/unpacking_non_sequence.py

@@ -4,6 +4,7 @@
 # pylint: disable=using-constant-test, no-init, missing-docstring, wrong-import-order,wrong-import-position,no-else-return, useless-object-inheritance
 from os import rename as nonseq_func
 from functional.u.unpacking import nonseq
+from typing import NamedTuple
 
 __revision__ = 0
 
@@ -137,3 +138,12 @@ def flow_control_unpacking(var=None):
         var0, var1 = var
         return var0, var1
     return None
+
+
+class MyClass(NamedTuple):
+    x: float
+    y: float
+
+    def sum(self):
+        x, y = self
+        return x + y

tests/functional/u/unpacking_non_sequence.txt

@@ -1,10 +1,10 @@
-unpacking-non-sequence:77:0:77:15::Attempting to unpack a non-sequence defined at line 74:UNDEFINED
-unpacking-non-sequence:78:0:78:17::Attempting to unpack a non-sequence:UNDEFINED
-unpacking-non-sequence:79:0:79:11::Attempting to unpack a non-sequence None:UNDEFINED
-unpacking-non-sequence:80:0:80:8::Attempting to unpack a non-sequence 1:UNDEFINED
-unpacking-non-sequence:81:0:81:13::Attempting to unpack a non-sequence defined at line 9 of functional.u.unpacking:UNDEFINED
-unpacking-non-sequence:82:0:82:15::Attempting to unpack a non-sequence defined at line 11 of functional.u.unpacking:UNDEFINED
-unpacking-non-sequence:83:0:83:18::Attempting to unpack a non-sequence:UNDEFINED
-unpacking-non-sequence:98:8:98:33:ClassUnpacking.test:Attempting to unpack a non-sequence defined at line 74:UNDEFINED
-unpacking-non-sequence:99:8:99:35:ClassUnpacking.test:Attempting to unpack a non-sequence:UNDEFINED
-unpacking-non-sequence:100:8:100:31:ClassUnpacking.test:Attempting to unpack a non-sequence:UNDEFINED
+unpacking-non-sequence:78:0:78:15::Attempting to unpack a non-sequence defined at line 75:UNDEFINED
+unpacking-non-sequence:79:0:79:17::Attempting to unpack a non-sequence:UNDEFINED
+unpacking-non-sequence:80:0:80:11::Attempting to unpack a non-sequence None:UNDEFINED
+unpacking-non-sequence:81:0:81:8::Attempting to unpack a non-sequence 1:UNDEFINED
+unpacking-non-sequence:82:0:82:13::Attempting to unpack a non-sequence defined at line 9 of functional.u.unpacking:UNDEFINED
+unpacking-non-sequence:83:0:83:15::Attempting to unpack a non-sequence defined at line 11 of functional.u.unpacking:UNDEFINED
+unpacking-non-sequence:84:0:84:18::Attempting to unpack a non-sequence:UNDEFINED
+unpacking-non-sequence:99:8:99:33:ClassUnpacking.test:Attempting to unpack a non-sequence defined at line 75:UNDEFINED
+unpacking-non-sequence:100:8:100:35:ClassUnpacking.test:Attempting to unpack a non-sequence:UNDEFINED
+unpacking-non-sequence:101:8:101:31:ClassUnpacking.test:Attempting to unpack a non-sequence:UNDEFINED