Fix pylint regression with invalid format strings (#2496)

Catch exceptions when calling string.format

Author: ericvergnaud

ChangeLog

@@ -13,6 +13,9 @@ What's New in astroid 3.3.1?
 ============================
 Release date: TBA
 
+* Fix a crash introduced in 3.3.0 involving invalid format strings.
+
+ Closes #2492
 
 
 What's New in astroid 3.3.0?

astroid/nodes/node_classes.py

@@ -4687,19 +4687,24 @@ def _infer(
  uninferable_already_generated = True
  continue
  for value in self.value.infer(context, **kwargs):
- if not isinstance(value, Const):
- if not uninferable_already_generated:
- yield util.Uninferable
- uninferable_already_generated = True
- continue
- formatted = format(value.value, format_spec.value)
- yield Const(
- formatted,
- lineno=self.lineno,
- col_offset=self.col_offset,
- end_lineno=self.end_lineno,
- end_col_offset=self.end_col_offset,
- )
+ if isinstance(value, Const):
+ try:
+ formatted = format(value.value, format_spec.value)
+ yield Const(
+ formatted,
+ lineno=self.lineno,
+ col_offset=self.col_offset,
+ end_lineno=self.end_lineno,
+ end_col_offset=self.end_col_offset,
+ )
+ continue
+ except (ValueError, TypeError):
+ # happens when format_spec.value is invalid
+ pass # fall through
+ if not uninferable_already_generated:
+ yield util.Uninferable
+ uninferable_already_generated = True
+ continue
 
 
 MISSING_VALUE = "{MISSING_VALUE}"

tests/test_inference.py

@@ -666,21 +666,6 @@ def test_fstring_inference(self) -> None:
  self.assertIsInstance(value_node, Const)
  self.assertEqual(value_node.value, "Hello John!")
 
- def test_formatted_fstring_inference(self) -> None:
- code = """
- width = 10
- precision = 4
- value = 12.34567
- result = f"result: {value:{width}.{precision}}!"
- """
- ast = parse(code, __name__)
- node = ast["result"]
- inferred = node.inferred()
- self.assertEqual(len(inferred), 1)
- value_node = inferred[0]
- self.assertIsInstance(value_node, Const)
- self.assertEqual(value_node.value, "result: 12.35!")
-
  def test_float_complex_ambiguity(self) -> None:
  code = '''
  def no_conjugate_member(magic_flag): #@
@@ -5517,6 +5502,51 @@ class instance(object):
  self.assertIsInstance(inferred, Instance)
 
 
+@pytest.mark.parametrize(
+ "code, result",
+ [
+ # regular f-string
+ (
+ """width = 10
+precision = 4
+value = 12.34567
+result = f"result: {value:{width}.{precision}}!"
+""",
+ "result: 12.35!",
+ ),
+ # unsupported format
+ (
+ """width = None
+precision = 4
+value = 12.34567
+result = f"result: {value:{width}.{precision}}!"
+""",
+ None,
+ ),
+ # unsupported value
+ (
+ """width = 10
+precision = 4
+value = None
+result = f"result: {value:{width}.{precision}}!"
+""",
+ None,
+ ),
+ ],
+)
+def test_formatted_fstring_inference(code, result) -> None:
+ ast = parse(code, __name__)
+ node = ast["result"]
+ inferred = node.inferred()
+ assert len(inferred) == 1
+ value_node = inferred[0]
+ if result is None:
+ assert value_node is util.Uninferable
+ else:
+ assert isinstance(value_node, Const)
+ assert value_node.value == result
+
+
 def test_augassign_recursion() -> None:
  """Make sure inference doesn't throw a RecursionError.