Don't crash on invalid strings when checking for `logging-format-interpolation`

Close #1944

3 files changed, 18 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 64f296049..7a85b01b3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,7 @@
 Pylint's ChangeLog
 ------------------
 
+<<<<<<< HEAD
 What's New in Pylint 1.8.3?
 ==========================
 
@@ -17,6 +18,10 @@ Release date: -
       `__doc__` can be used to specify a docstring for a module without
       passing it as a first-statement string.
 
+    * Don't crash on invalid strings when checking for `logging-format-interpolation`
+
+      Close #1944
+
     * Fix false positive ``inconsistent-return-statements`` message by
       avoiding useless exception inference if the exception is not handled.
 
diff --git a/pylint/checkers/logging.py b/pylint/checkers/logging.py
index 051fa7589..f87242fb2 100644
--- a/pylint/checkers/logging.py
+++ b/pylint/checkers/logging.py
@@ -263,7 +263,12 @@ def is_complex_format_str(node):
     inferred = utils.safe_infer(node)
     if inferred is None or not isinstance(inferred.value, six.string_types):
         return True
-    for _, _, format_spec, _ in string.Formatter().parse(inferred.value):
+    try:
+        parsed = list(string.Formatter().parse(inferred.value))
+    except ValueError:
+        # This format string is invalid
+        return False
+    for _, _, format_spec, _ in parsed:
         if format_spec:
             return True
     return False
diff --git a/pylint/test/unittest_checker_logging.py b/pylint/test/unittest_checker_logging.py
index 6075a2a2e..a87c3f542 100644
--- a/pylint/test/unittest_checker_logging.py
+++ b/pylint/test/unittest_checker_logging.py
@@ -27,6 +27,13 @@ class TestLoggingModuleDetection(CheckerTestCase):
         with self.assertAddsMessages(Message('logging-not-lazy', node=stmts[1])):
             self.checker.visit_call(stmts[1])
 
+    def test_dont_crash_on_invalid_format_string(self):
+        node = astroid.parse('''
+        import logging
+        logging.error('0} - {1}'.format(1, 2))
+        ''')
+        self.walk(node)
+
     def test_detects_renamed_standard_logging_module(self):
         stmts = astroid.extract_node("""
         import logging as blogging #@