Merge; Fix according to review

1 files changed, 41 insertions, 3 deletions

diff --git a/checkers/stdlib.py b/checkers/stdlib.py
index d8b5fde..54f8c1a 100644
--- a/checkers/stdlib.py
+++ b/checkers/stdlib.py
@@ -16,6 +16,7 @@
 """Checkers for various standard library functions."""
 
 import re
+import six
 import sys
 
 import astroid
@@ -25,13 +26,50 @@ from pylint.interfaces import IAstroidChecker
 from pylint.checkers import BaseChecker
 from pylint.checkers import utils
 
-_VALID_OPEN_MODE_REGEX = re.compile(r'^(r?U|[rwa]\+?b?)$')
 
 if sys.version_info >= (3, 0):
     OPEN_MODULE = '_io'
 else:
     OPEN_MODULE = '__builtin__'
 
+
+def _check_mode_str(mode):
+    # check type
+    if not isinstance(mode, six.string_types):
+        return False
+    # check syntax
+    modes = set(mode)
+    _mode = "rwatb+U"
+    if six.PY3:
+        _mode += "x"
+        creating = "x" in modes
+    if modes - set(_mode) or len(mode) > len(modes):
+        return False
+    # check logic
+    creating = False
+    reading = "r" in modes
+    writing = "w" in modes
+    appending = "a" in modes
+    updating = "+" in modes
+    text = "t" in modes
+    binary = "b" in modes
+    if "U" in modes:
+        if writing or appending or creating and six.PY3:
+            return False
+        reading = True
+    if text and binary:
+        return False
+    total = reading + writing + appending + (creating if six.PY3 else 0)
+    if total > 1:
+        return False
+    if not (reading or writing or appending or creating and six.PY3):
+        return False
+    # 2.x constraints
+    if not six.PY3:
+        return mode[0] in ("r", "w", "a", "U")
+    return True
+
+
 class StdlibChecker(BaseChecker):
     __implements__ = (IAstroidChecker,)
     name = 'stdlib'
@@ -89,6 +127,7 @@ class StdlibChecker(BaseChecker):
                 infered.qname() == 'datetime.time'):
             self.add_message('boolean-datetime', node=node)
 
+
     def _check_open_mode(self, node):
         """Check that the mode argument of an open or file call is valid."""
         try:
@@ -96,7 +135,7 @@ class StdlibChecker(BaseChecker):
             if mode_arg:
                 mode_arg = utils.safe_infer(mode_arg)
                 if (isinstance(mode_arg, astroid.Const)
-                        and not _VALID_OPEN_MODE_REGEX.match(mode_arg.value)):
+                        and not _check_mode_str(mode_arg.value)):
                     self.add_message('bad-open-mode', node=node,
                                      args=(mode_arg.value))
         except (utils.NoSuchArgumentError, TypeError):
@@ -105,4 +144,3 @@ class StdlibChecker(BaseChecker):
 def register(linter):
     """required method to auto register this checker """
     linter.register_checker(StdlibChecker(linter))
-