Add ConfigurationError and use it.

pip/commands/configuration.py

@@ -4,6 +4,7 @@ import subprocess
 from pip import cmdoptions
 from pip.basecommand import Command
 from pip.configuration import Configuration
+from pip.exceptions import ConfigurationError
 from pip.status_codes import SUCCESS, ERROR
 
 logger = logging.getLogger(__name__)
@@ -203,18 +204,22 @@ class ConfigurationCommand(Command):
 
     def set_name_value(self, options):
         key, value = options.set_name_value.split("=", 1)
-        self.configuration.set_value(key, value)  # Error here is propagated.
 
+        try:
+            self.configuration.set_value(key, value)
+        except ConfigurationError:
+            logger.error("Could not set value in configuration")
+        else:
         return self._save_configuration()
 
     def unset_name(self, options):
         key = options.unset_name
-        val = self.configuration.unset_value(key)  # Error here is propagated.
-
-        if val is False:
-            logger.warn("ERROR: No key %r in configuration", key)
-            return ERROR
 
+        try:
+            self.configuration.unset_value(key)
+        except ConfigurationError:
+            logger.error("Could not unset value in configuration")
+        else:
         return self._save_configuration()
 
     def _save_configuration(self):

pip/configuration.py

@@ -18,6 +18,7 @@ import logging
 from pip._vendor.six import next
 from pip._vendor.six.moves import configparser
 
+from pip.exceptions import ConfigurationError
 from pip.locations import (
     legacy_config_file, new_config_file, running_under_virtualenv,
     site_config_files, venv_config_file
@@ -67,7 +68,7 @@ class Configuration(object):
         super(Configuration, self).__init__()
 
         if load_only not in ["user", "site-wide", "venv", None]:
-            raise ValueError(
+            raise ConfigurationError(
                 "Got invalid value for load_only - should be one of 'user', "
                 "'site-wide', 'venv'"
             )
@@ -127,7 +128,7 @@ class Configuration(object):
         assert self.load_only is not None, _need_file_err_msg
 
         if key not in self._config[self.load_only]:
-            raise KeyError(key)
+            raise ConfigurationError(key)
 
         file, parser = self._get_parser_to_modify()
 
@@ -150,9 +151,9 @@ class Configuration(object):
                 if file_parser_tuple not in self._modified_parsers:
                     self._modified_parsers.append(file_parser_tuple)
             else:
-                # If here, something is there in the dictionary but not in the
-                # parser. This should not happen.
-                pass
+                raise ConfigurationError(
+                    "Internal error [id=1]. Please report as a bug."
+                )
 
         del self._config[self.load_only][key]
 
@@ -277,8 +278,10 @@ class Configuration(object):
         # Determine which parser to modify
         parsers = self._parsers[self.load_only]
         if not parsers:
-            # This should not happen if we're doing it correctly.
-            raise Exception("Internal configuration error!?")
+            # This should not happen if everything works correctly.
+            raise ConfigurationError(
+                "Internal error [id=2]. Please report as a bug."
+            )
 
         # Use the highest priority parser.
         return parsers[-1]

pip/exceptions.py

@@ -10,6 +10,10 @@ class PipError(Exception):
     """Base pip exception"""
 
 
+class ConfigurationError(PipError):
+    """General exception in configuration"""
+
+
 class InstallationError(PipError):
     """General exception during installation"""