Improve handling of assignment expressions

ChangeLog

@@ -71,6 +71,10 @@ Release date: TBA
 
   Closes #4218
 
+* Improve handling of assignment expressions, better edge case handling
+
+  Closes #3763, #4238
+
 
 What's New in Pylint 2.7.2?
 ===========================

pylint/checkers/variables.py

@@ -59,6 +59,7 @@
 
 from pylint.checkers import BaseChecker, utils
 from pylint.checkers.utils import is_postponed_evaluation_enabled
+from pylint.constants import PY39_PLUS
 from pylint.interfaces import HIGH, INFERENCE, INFERENCE_FAILURE, IAstroidChecker
 from pylint.utils import get_global_option
 
@@ -1410,7 +1411,15 @@ def _is_variable_violation(
                     # same line as the function definition
                     maybee0601 = False
                 elif (
-                    isinstance(defstmt, astroid.Assign)
+                    isinstance(
+                        defstmt,
+                        (
+                            astroid.Assign,
+                            astroid.AnnAssign,
+                            astroid.AugAssign,
+                            astroid.Expr,
+                        ),
+                    )
                     and isinstance(defstmt.value, astroid.IfExp)
                     and frame is defframe
                     and defframe.parent_of(node)
@@ -1433,6 +1442,18 @@ def _is_variable_violation(
                             and defnode.col_offset < node.col_offset
                         )
                         or (defnode.lineno < node.lineno)
+                        or (
+                            # Issue in the `ast` module until py39
+                            # Nodes in a multiline string have the same lineno
+                            # Could be false-positive without check
+                            not PY39_PLUS
+                            and defnode.lineno == node.lineno
+                            and isinstance(
+                                defstmt,
+                                (astroid.Assign, astroid.AnnAssign, astroid.AugAssign),
+                            )
+                            and isinstance(defstmt.value, astroid.JoinedStr)
+                        )
                     )
                 ):
                     # Expressions, with assignment expressions

pylint/constants.py

@@ -8,6 +8,7 @@
 from pylint.__pkginfo__ import version as pylint_version
 
 PY38_PLUS = sys.version_info[:2] >= (3, 8)
+PY39_PLUS = sys.version_info[:2] >= (3, 9)
 PY310_PLUS = sys.version_info[:2] >= (3, 10)
 
 

tests/functional/a/assignment_expression.py

@@ -8,6 +8,9 @@
     x = False
 
 x = b if (b := True) else False
+x2: bool = b2 if (b2 := True) else False
+x3 = 0
+x3 += b3 if (b3 := 4) else 6
 
 a = ["a   ", "b   ", "c   "]
 c = [text for el in a if (text := el.strip()) == "b"]
@@ -49,6 +52,24 @@ def func():
 print(function())
 
 
+# https://github.com/PyCQA/pylint/issues/3763
+foo if (foo := 3 - 2) > 0 else 0  # [pointless-statement]
+
+
+# https://github.com/PyCQA/pylint/issues/4238
+l1 = f'The number {(count1 := 4)} ' \
+     f'is equal to {count1}'
+l2: str = (
+    f'The number {(count2 := 4)} '
+    f'is equal to {count2}'
+)
+l3 = "Hello "
+l3 += (
+    f'The number {(count3 := 4)} '
+    f'is equal to {count3}'
+)
+
+
 # check wrong usage
 assert err_a, (err_a := 2)  # [used-before-assignment]
 print(err_b and (err_b := 2))  # [used-before-assignment]

tests/functional/a/assignment_expression.txt

@@ -1,3 +1,4 @@
-used-before-assignment:53:7::Using variable 'err_a' before assignment
-used-before-assignment:54:6::Using variable 'err_b' before assignment
-used-before-assignment:56:13::Using variable 'err_d' before assignment
+pointless-statement:56:0::Statement seems to have no effect
+used-before-assignment:74:7::Using variable 'err_a' before assignment
+used-before-assignment:75:6::Using variable 'err_b' before assignment
+used-before-assignment:77:13::Using variable 'err_d' before assignment