old_contents: from __future__ import division, absolute_import, print_function
  
  from .util import BASESTRING
  from . import yaml_util
  import os
  
  __all__ = ['ConfigSource']
  
  
  class ConfigSource(dict):
      """A dictionary augmented with metadata about the source of the
      configuration.
      """
      def __init__(self, value, filename=None, default=False):
          super(ConfigSource, self).__init__(value)
          if (filename is not None
                  and not isinstance(filename, BASESTRING)):
              raise TypeError(u'filename must be a string or None')
          self.filename = filename
          self.default = default
  
      def __repr__(self):
          return 'ConfigSource({0!r}, {1!r}, {2!r})'.format(
              super(ConfigSource, self),
              self.filename,
              self.default,
          )
  
      @classmethod
      def of(cls, value):
          """Given either a dictionary or a `ConfigSource` object, return
          a `ConfigSource` object. This lets a function accept either type
          of object as an argument.
          """
          if isinstance(value, ConfigSource):
              return value
          elif isinstance(value, dict):
              return ConfigSource(value)
          else:
              raise TypeError(u'source value must be a dict')
  
  
  class YamlSource(ConfigSource):
      """A configuration data source that reads from a YAML file.
      """
  
      def __init__(self, filename=None, default=False,
                   optional=False, loader=yaml_util.Loader):
          """Create a YAML data source by reading data from a file.
  
          May raise a `ConfigReadError`. However, if `optional` is
          enabled, this exception will not be raised in the case when the
          file does not exist---instead, the source will be silently
          empty.
          """
          if optional and not os.path.isfile(filename):
              value = {}
          else:
              value = yaml_util.load_yaml(filename, loader=loader) or {}
          super(YamlSource, self).__init__(value, filename, default)
  
new_contents: from __future__ import division, absolute_import, print_function
  
  from .util import BASESTRING
  from . import yaml_util
  import os
  
  
  class ConfigSource(dict):
      """A dictionary augmented with metadata about the source of the
      configuration.
      """
      def __init__(self, value, filename=None, default=False):
          super(ConfigSource, self).__init__(value)
          if (filename is not None
                  and not isinstance(filename, BASESTRING)):
              raise TypeError(u'filename must be a string or None')
          self.filename = filename
          self.default = default
  
      def __repr__(self):
          return 'ConfigSource({0!r}, {1!r}, {2!r})'.format(
              super(ConfigSource, self),
              self.filename,
              self.default,
          )
  
      @classmethod
      def of(cls, value):
          """Given either a dictionary or a `ConfigSource` object, return
          a `ConfigSource` object. This lets a function accept either type
          of object as an argument.
          """
          if isinstance(value, ConfigSource):
              return value
          elif isinstance(value, dict):
              return ConfigSource(value)
          else:
              raise TypeError(u'source value must be a dict')
  
  
  class YamlSource(ConfigSource):
      """A configuration data source that reads from a YAML file.
      """
  
      def __init__(self, filename=None, default=False,
                   optional=False, loader=yaml_util.Loader):
          """Create a YAML data source by reading data from a file.
  
          May raise a `ConfigReadError`. However, if `optional` is
          enabled, this exception will not be raised in the case when the
          file does not exist---instead, the source will be silently
          empty.
          """
          if optional and not os.path.isfile(filename):
              value = {}
          else:
              value = yaml_util.load_yaml(filename, loader=loader) or {}
          super(YamlSource, self).__init__(value, filename, default)
  
subject: Remove an __all__ definition