Add E243 for whitespace around attribute access

docs/intro.rst

@@ -292,6 +292,8 @@ This is the current list of error and warning codes:
 +------------+----------------------------------------------------------------------+
 | E242 (*)   | tab after ','                                                        |
 +------------+----------------------------------------------------------------------+
+| E243 (*)   | whitespace around attribute access                                   |
++------------+----------------------------------------------------------------------+
 +------------+----------------------------------------------------------------------+
 | E251       | unexpected spaces around keyword / parameter equals                  |
 +------------+----------------------------------------------------------------------+
@@ -418,7 +420,7 @@ This is the current list of error and warning codes:
 
 
 **(*)** In the default configuration, the checks **E121**, **E123**, **E126**, **E133**,
-**E226**, **E241**, **E242**, **E704**, **W503**, **W504** and **W505** are ignored
+**E226**, **E241**, **E242**, **E243**, **E704**, **W503**, **W504** and **W505** are ignored
 because they are not rules unanimously accepted, and `PEP 8`_ does not enforce them.
 Please note that if the option ``--ignore=errors`` is used,
 the default configuration will be overridden and ignore only the check(s) you skip.

pycodestyle.py

@@ -803,6 +803,52 @@ def whitespace_before_parameters(logical_line, tokens):
         prev_end = end
 
 
+def _is_attribute_access_operand(token_type, text):
+    return (
+        (
+            token_type in {tokenize.NAME, tokenize.NUMBER, tokenize.STRING} and
+            not keyword.iskeyword(text) and
+            not keyword.issoftkeyword(text)
+        ) or
+        text in '}])'
+    )
+
+
+@register_check
+def whitespace_around_attribute_access(logical_line, tokens):
+    r"""Avoid extraneous whitespace around attribute access.
+
+    Note: these checks are disabled by default
+
+    Okay: spam.eggs
+    E243: spam .eggs
+    E243: spam. eggs
+    """
+    prev_type, prev_text, __, prev_end, __ = tokens[0]
+    for index in range(1, len(tokens) - 1):
+        token_type, text, start, end, __ = tokens[index]
+        next_type, __, next_start, __, __ = tokens[index + 1]
+        is_attribute_dot = (
+            token_type == tokenize.OP and
+            text == '.' and
+            start[0] == prev_end[0] and
+            _is_attribute_access_operand(prev_type, prev_text)
+        )
+        if is_attribute_dot:
+            if start != prev_end:
+                yield prev_end, "E243 whitespace before '.'"
+            if (
+                    next_type == tokenize.NAME and
+                    next_start[0] == end[0] and
+                    next_start != end
+            ):
+                yield end, "E243 whitespace after '.'"
+
+        prev_type = token_type
+        prev_text = text
+        prev_end = end
+
+
 @register_check
 def whitespace_around_operator(logical_line):
     r"""Avoid extraneous whitespace around an operator.

testing/data/E24.py

@@ -11,3 +11,19 @@
 more_spaces = [a,    b,
                ef,  +h,
                c,   -d]
+#: E243:1:5
+spam .eggs
+#: E243:1:6
+spam. eggs
+#: E243:1:5 E243:1:7
+spam . eggs
+#: Okay
+spam.eggs
+#: Okay
+from . import eggs
+from ..spam import eggs
+#: Okay
+(
+    spam
+    .eggs
+)