Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/confuse/exceptions.py

@@ -0,0 +1,56 @@
+from __future__ import division, absolute_import, print_function
+
+import yaml
+
+__all__ = [
+    'ConfigError', 'NotFoundError', 'ConfigValueError', 'ConfigTypeError',
+    'ConfigTemplateError', 'ConfigReadError']
+
+YAML_TAB_PROBLEM = "found character '\\t' that cannot start any token"
+
+# Exceptions.
+
+
+class ConfigError(Exception):
+    """Base class for exceptions raised when querying a configuration.
+    """
+
+
+class NotFoundError(ConfigError):
+    """A requested value could not be found in the configuration trees.
+    """
+
+
+class ConfigValueError(ConfigError):
+    """The value in the configuration is illegal."""
+
+
+class ConfigTypeError(ConfigValueError):
+    """The value in the configuration did not match the expected type.
+    """
+
+
+class ConfigTemplateError(ConfigError):
+    """Base class for exceptions raised because of an invalid template.
+    """
+
+
+class ConfigReadError(ConfigError):
+    """A configuration source could not be read."""
+    def __init__(self, name, reason=None):
+        self.name = name
+        self.reason = reason
+
+        message = u'{0} could not be read'.format(name)
+        if (isinstance(reason, yaml.scanner.ScannerError)
+                and reason.problem == YAML_TAB_PROBLEM):
+            # Special-case error message for tab indentation in YAML markup.
+            message += u': found tab character at line {0}, column {1}'.format(
+                reason.problem_mark.line + 1,
+                reason.problem_mark.column + 1,
+            )
+        elif reason:
+            # Generic error message uses exception's message.
+            message += u': {0}'.format(reason)
+
+        super(ConfigReadError, self).__init__(message)