Merge pull request #5644 from sinscary/fix_invalid_val_error

Show appropriate error message

news/5644.bugfix

@@ -0,0 +1 @@
+Show a better error message when a configuration option has an invalid value.

src/pip/_internal/baseparser.py

@@ -192,7 +192,14 @@ def _update_defaults(self, defaults):
                 continue
 
             if option.action in ('store_true', 'store_false', 'count'):
-                val = strtobool(val)
+                try:
+                    val = strtobool(val)
+                except ValueError:
+                    error_msg = invalid_config_error_message(
+                        option.action, key, val
+                    )
+                    self.error(error_msg)
+
             elif option.action == 'append':
                 val = val.split()
                 val = [self.check_default(option, key, v) for v in val]
@@ -238,3 +245,16 @@ def get_default_values(self):
     def error(self, msg):
         self.print_usage(sys.stderr)
         self.exit(2, "%s\n" % msg)
+
+
+def invalid_config_error_message(action, key, val):
+    """Returns a better error message when invalid configuration option
+    is provided."""
+    if action in ('store_true', 'store_false'):
+        return ("{0} is not a valid value for {1} option, "
+                "please specify a boolean value like yes/no, "
+                "true/false or 1/0 instead.").format(val, key)
+
+    return ("{0} is not a valid value for {1} option, "
+            "please specify a numerical value like 1/0 "
+            "instead.").format(val, key)