old_contents: from __future__ import absolute_import
  from __future__ import unicode_literals
  
  
  VERSION_EXPLANATION = (
      'You might be seeing this error because you\'re using the wrong Compose file version. '
      'Either specify a supported version ("2.0", "2.1", "3.0", "3.1", "3.2") and place '
      'your service definitions under the `services` key, or omit the `version` key '
      'and place your service definitions at the root of the file to use '
      'version 1.\nFor more on the Compose file format versions, see '
      'https://docs.docker.com/compose/compose-file/')
  
  
  class ConfigurationError(Exception):
      def __init__(self, msg):
          self.msg = msg
  
      def __str__(self):
          return self.msg
  
  
  class DependencyError(ConfigurationError):
      pass
  
  
  class CircularReference(ConfigurationError):
      def __init__(self, trail):
          self.trail = trail
  
      @property
      def msg(self):
          lines = [
              "{} in {}".format(service_name, filename)
              for (filename, service_name) in self.trail
          ]
          return "Circular reference:\n  {}".format("\n  extends ".join(lines))
  
  
  class ComposeFileNotFound(ConfigurationError):
      def __init__(self, supported_filenames):
          super(ComposeFileNotFound, self).__init__("""
          Can't find a suitable configuration file in this directory or any
          parent. Are you in the right directory?
  
          Supported filenames: %s
          """ % ", ".join(supported_filenames))
  
  
  class DuplicateOverrideFileFound(ConfigurationError):
      def __init__(self, override_filenames):
          self.override_filenames = override_filenames
  
      @property
      def msg(self):
          return """
          Unable to determine with duplicate override files, only a single override file can be used.
          Found: %s
          """ % ", ".join(self.override_filenames)
  
new_contents: from __future__ import absolute_import
  from __future__ import unicode_literals
  
  
  VERSION_EXPLANATION = (
      'You might be seeing this error because you\'re using the wrong Compose file version. '
      'Either specify a supported version ("2.0", "2.1", "3.0", "3.1", "3.2") and place '
      'your service definitions under the `services` key, or omit the `version` key '
      'and place your service definitions at the root of the file to use '
      'version 1.\nFor more on the Compose file format versions, see '
      'https://docs.docker.com/compose/compose-file/')
  
  
  class ConfigurationError(Exception):
      def __init__(self, msg):
          self.msg = msg
  
      def __str__(self):
          return self.msg
  
  
  class DependencyError(ConfigurationError):
      pass
  
  
  class CircularReference(ConfigurationError):
      def __init__(self, trail):
          self.trail = trail
  
      @property
      def msg(self):
          lines = [
              "{} in {}".format(service_name, filename)
              for (filename, service_name) in self.trail
          ]
          return "Circular reference:\n  {}".format("\n  extends ".join(lines))
  
  
  class ComposeFileNotFound(ConfigurationError):
      def __init__(self, supported_filenames):
          super(ComposeFileNotFound, self).__init__("""
          Can't find a suitable configuration file in this directory or any
          parent. Are you in the right directory?
  
          Supported filenames: %s
          """ % ", ".join(supported_filenames))
  
  
  class DuplicateOverrideFileFound(ConfigurationError):
      def __init__(self, override_filenames):
          self.override_filenames = override_filenames
          super(DuplicateOverrideFileFound, self).__init__(
              "Multiple override files found: {}. You may only use a single "
              "override file.".format(", ".join(override_filenames))
          )
  
subject: Rewrite duplicate override error message