avoid interpreting IOError in config file as file-not-found

adds ConfigFileNotFound exception class for this case

IPython/config/application.py

@@ -27,7 +27,7 from copy import deepcopy
 
 from IPython.config.configurable import SingletonConfigurable
 from IPython.config.loader import (
-    KVArgParseConfigLoader, PyFileConfigLoader, Config, ArgumentError
+    KVArgParseConfigLoader, PyFileConfigLoader, Config, ArgumentError, ConfigFileNotFound,
 )
 
 from IPython.utils.traitlets import (
@@ -370,8 +370,8 class Application(SingletonConfigurable):
         loader = PyFileConfigLoader(filename, path=path)
         try:
             config = loader.load_config()
-        except IOError:
-            # problem with the file (probably doesn't exist), raise
+        except ConfigFileNotFound:
+            # problem finding the file, raise
             raise
         except Exception:
             # try to get the full filename, but it will be empty in the

IPython/config/loader.py

@@ -34,10 +34,12 from IPython.utils import py3compat, text, warn
 class ConfigError(Exception):
     pass
 
-
 class ConfigLoaderError(ConfigError):
     pass
 
+class ConfigFileNotFound(ConfigError):
+    pass
+
 class ArgumentError(ConfigLoaderError):
     pass
 
@@ -258,7 +260,10 class PyFileConfigLoader(FileConfigLoader):
     def load_config(self):
         """Load the config from a file and return it as a Struct."""
         self.clear()
-        self._find_file()
+        try:
+            self._find_file()
+        except IOError as e:
+            raise ConfigFileNotFound(str(e))
         self._read_file_as_dict()
         self._convert_to_config()
         return self.config
@@ -297,7 +302,7 class PyFileConfigLoader(FileConfigLoader):
             loader = PyFileConfigLoader(fname, path)
             try:
                 sub_config = loader.load_config()
-            except IOError:
+            except ConfigFileNotFound:
                 # Pass silently if the sub config is not there. This happens
                 # when a user s using a profile, but not the default config.
                 pass