Issue #18873: IDLE, 2to3, and the findnocoding.py script now detect Python

source code encoding only in comment lines.

Lib/idlelib/IOBinding.py

@@ -71,7 +71,7 @@ else:
 
 encoding = encoding.lower()
 
-coding_re = re.compile("coding[:=]\s*([-\w_.]+)")
+coding_re = re.compile(r'^[ \t\f]*#.*coding[:=][ \t]*([-\w.]+)', re.ASCII)
 
 class EncodingMessage(SimpleDialog):
     "Inform user that an encoding declaration is needed."
@@ -125,11 +125,12 @@ def coding_spec(str):
     Raise LookupError if the encoding is declared but unknown.
     """
     # Only consider the first two lines
-    str = str.split("\n")[:2]
-    str = "\n".join(str)
-
-    match = coding_re.search(str)
-    if not match:
+    str = str.split("\n", 2)[:2]
+    for line in lst:
+        match = coding_re.match(line)
+        if match is not None:
+            break
+    else:
         return None
     name = match.group(1)
     # Check whether the encoding is known

Lib/lib2to3/pgen2/tokenize.py

@@ -236,7 +236,7 @@ class Untokenizer:
                 startline = False
             toks_append(tokval)
 
-cookie_re = re.compile("coding[:=]\s*([-\w.]+)")
+cookie_re = re.compile(r'^[ \t\f]*#.*coding[:=][ \t]*([-\w.]+)', re.ASCII)
 
 def _get_normal_name(orig_enc):
     """Imitates get_normal_name in tokenizer.c."""
@@ -281,11 +281,10 @@ def detect_encoding(readline):
             line_string = line.decode('ascii')
         except UnicodeDecodeError:
             return None
-
-        matches = cookie_re.findall(line_string)
-        if not matches:
+        match = cookie_re.match(line_string)
+        if not match:
             return None
-        encoding = _get_normal_name(matches[0])
+        encoding = _get_normal_name(match.group(1))
         try:
             codec = lookup(encoding)
         except LookupError:

Lib/lib2to3/tests/data/false_encoding.py

+#!/usr/bin/env python
+print '#coding=0'

Lib/lib2to3/tests/test_refactor.py

@@ -271,6 +271,10 @@ from __future__ import print_function"""
         fn = os.path.join(TEST_DATA_DIR, "different_encoding.py")
         self.check_file_refactoring(fn)
 
+    def test_false_file_encoding(self):
+        fn = os.path.join(TEST_DATA_DIR, "false_encoding.py")
+        data = self.check_file_refactoring(fn)
+
     def test_bom(self):
         fn = os.path.join(TEST_DATA_DIR, "bom.py")
         data = self.check_file_refactoring(fn)

Misc/NEWS

@@ -183,6 +183,9 @@ Library
 Tools/Demos
 -----------
 
+- Issue #18873: 2to3 and the findnocoding.py script now detect Python source
+  code encoding only in comment lines.
+
 - Issue #18817: Fix a resource warning in Lib/aifc.py demo.
 
 - Issue #18439: Make patchcheck work on Windows for ACKS, NEWS.
@@ -207,6 +210,9 @@ Build
 IDLE
 ----
 
+- Issue #18873: IDLE now detects Python source code encoding only in comment
+  lines.
+
 - Issue #18988: The "Tab" key now works when a word is already autocompleted.
 
 - Issue #18489: Add tests for SearchEngine. Original patch by Phil Webster.

Tools/scripts/findnocoding.py

@@ -32,13 +32,13 @@ except ImportError:
                          "no sophisticated Python source file search will be done.")
 
 
-decl_re = re.compile(r"coding[=:]\s*([-\w.]+)")
+decl_re = re.compile(r'^[ \t\f]*#.*coding[:=][ \t]*([-\w.]+)', re.ASCII)
 
 def get_declaration(line):
-    match = decl_re.search(line)
+    match = decl_re.match(line)
     if match:
         return match.group(1)
-    return ''
+    return b''
 
 def has_correct_encoding(text, codec):
     try: