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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_hostname_prefix():
 """Returns the hostname prefix of a running Endpoints service. The prefix is the portion of the hostname that comes before the API name. For example, if a non-default version and a non-default service are in use, the returned result would be '{VERSION}-dot-{SERVICE}-'. Returns: str, the hostname prefix. """

  parts = []

  # Check if this is the default version
  version = modules.get_current_version_name()
  default_version = modules.get_default_version()
  if version != default_version:
    parts.append(version)

  # Check if this is the default module
  module = modules.get_current_module_name()
  if module != 'default':
    parts.append(module)

  # If there is anything to prepend, add an extra blank entry for the trailing
  # -dot-
  if parts:
    parts.append('')

  return '-dot-'.join(parts)