E403: add report for module-level dunder names that are misplaced.

docs/intro.rst

@@ -335,6 +335,8 @@ This is the current list of error and warning codes:
 +------------+----------------------------------------------------------------------+
 | E402       | module level import not at top of file                               |
 +------------+----------------------------------------------------------------------+
+| E403       | module level dunder name found after non-future imports              |
++------------+----------------------------------------------------------------------+
 +------------+----------------------------------------------------------------------+
 | **E5**     | *Line length*                                                        |
 +------------+----------------------------------------------------------------------+

pycodestyle.py

@@ -46,6 +46,9 @@
 700 statements
 900 syntax error
 """
+
+__version__ = '2.11.1'
+
 import bisect
 import configparser
 import inspect
@@ -68,8 +71,6 @@
 ):  # pragma: no cover (<py310)
     tokenize._compile = lru_cache(tokenize._compile)  # type: ignore
 
-__version__ = '2.11.1'
-
 DEFAULT_EXCLUDE = '.svn,CVS,.bzr,.hg,.git,__pycache__,.tox'
 DEFAULT_IGNORE = 'E121,E123,E126,E226,E24,E704,W503,W504'
 try:
@@ -378,6 +379,18 @@ def blank_lines(logical_line, blank_lines, indent_level, line_number,
             (indent_level and blank_lines == method_lines + 1)
           ):
         yield 0, "E303 too many blank lines (%d)" % blank_lines
+    elif DUNDER_REGEX.match(previous_logical):
+        if DUNDER_REGEX.match(logical_line):
+            return  # Allow groupings of dunder names
+        if not blank_lines:
+            yield 0, "E301 expected 1 blank line, found 0"
+        if blank_lines > 1:
+            yield 0, "E303 too many blank lines (%d)" % blank_lines
+    elif DUNDER_REGEX.match(logical_line):
+        if not blank_lines:
+            yield 0, "E301 expected 1 blank line, found 0"
+        if blank_lines > 1:
+            yield 0, "E303 too many blank lines (%d)" % blank_lines
     elif STARTSWITH_TOP_LEVEL_REGEX.match(logical_line):
         # allow a group of one-liners
         if (
@@ -1161,7 +1174,12 @@ def is_string_literal(line):
     if line.startswith('import ') or line.startswith('from '):
         if checker_state.get('seen_non_imports', False):
             yield 0, "E402 module level import not at top of file"
+        if line.split()[1] == '__future__':
+            return  # Allow before dunders - https://bugs.python.org/issue27187
+        checker_state['seen_imports'] = True
     elif re.match(DUNDER_REGEX, line):
+        if checker_state.get('seen_imports', False):
+            yield 0, "E403 module-level dunder name after non-future imports"
         return
     elif any(line.startswith(kw) for kw in allowed_keywords):
         # Allow certain keywords intermixed with imports in order to

testing/data/E30.py

@@ -203,3 +203,24 @@ def f():
 @hi
 def g():
     pass
+#: E303:4:1 E303:7:1
+from __future__ import annotations
+
+
+__all__ = ('xyz',)
+
+
+import foo
+#: E301:2:1 E301:3:1
+from __future__ import annotations
+__all__ = ('xyz',)
+import foo
+#: E303:8:1
+__all__ = ('together',)
+
+
+
+
+
+
+import foo

testing/data/E30not.py

@@ -213,3 +213,8 @@ def f(
     a,
 ):
     pass
+#: Okay
+from __future__ import annotations
+
+__all__ = ('not_lost',)
+__author__ = 'you'

testing/data/python38.py

@@ -28,7 +28,7 @@ def f3(
 #: E225:1:18
 if False or (x :=1):
     pass
-#: Okay
+#: E403:3:1
 import typing as t
 
 __all__: t.List[str] = []