Fix AttributeError when encoding detection returns None

.gitignore

@@ -16,3 +16,4 @@ htmlcov/
 .idea/
 .vscode/
 .tox/
+.venv/

src/docformatter/encode.py

@@ -42,9 +42,12 @@ class Encoder:
     LF = "\n"
     CRLF = "\r\n"
 
+    # Default encoding to use if the file encoding cannot be detected
+    DEFAULT_ENCODING = "latin-1"
+
     def __init__(self):
         """Initialize an Encoder instance."""
-        self.encoding = "latin-1"
+        self.encoding = self.DEFAULT_ENCODING
         self.system_encoding = locale.getpreferredencoding() or sys.getdefaultencoding()
 
     def do_detect_encoding(self, filename) -> None:
@@ -56,13 +59,16 @@ def do_detect_encoding(self, filename) -> None:
             The full path name of the file whose encoding is to be detected.
         """
         try:
-            self.encoding = from_path(filename).best().encoding
+            detection_result = from_path(filename).best()
+            self.encoding = (
+                detection_result.encoding if detection_result else self.DEFAULT_ENCODING
+            )
 
             # Check for correctness of encoding.
             with self.do_open_with_encoding(filename) as check_file:
                 check_file.read()
         except (SyntaxError, LookupError, UnicodeDecodeError):
-            self.encoding = "latin-1"
+            self.encoding = self.DEFAULT_ENCODING
 
     def do_find_newline(self, source: List[str]) -> str:
         """Return type of newline used in source.

tests/test_encoding_functions.py

@@ -83,6 +83,21 @@ def test_detect_encoding_with_bad_encoding(self, temporary_file, contents):
 
         assert "ascii" == uut.encoding
 
+    @pytest.mark.unit
+    @pytest.mark.parametrize("contents", [""])
+    def test_detect_encoding_with_undetectable_encoding(self, temporary_file):
+        """Default to latin-1 when encoding detection fails."""
+        uut = Encoder()
+
+        # Simulate a file with undetectable encoding
+        with open(temporary_file, "wb") as file:
+            # Binary content unlikely to have a detectable encoding
+            file.write(b"\xFF\xFE\xFD\xFC\x00\x00\x00\x00")
+
+        uut.do_detect_encoding(temporary_file)
+
+        assert uut.encoding == uut.DEFAULT_ENCODING
+
 
 class TestFindNewline:
     """Class for testing the find_newline() function."""