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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 AddExtensionDescriptor(self, extension):
 """Adds a FieldDescriptor describing an extension to the pool. Args: extension: A FieldDescriptor. Raises: AssertionError: when another extension with the same number extends the same message. TypeError: when the specified extension is not a descriptor.FieldDescriptor. """

    if not (isinstance(extension, descriptor.FieldDescriptor) and
            extension.is_extension):
      raise TypeError('Expected an extension descriptor.')

    if extension.extension_scope is None:
      self._toplevel_extensions[extension.full_name] = extension

    try:
      existing_desc = self._extensions_by_number[
          extension.containing_type][extension.number]
    except KeyError:
      pass
    else:
      if extension is not existing_desc:
        raise AssertionError(
            'Extensions "%s" and "%s" both try to extend message type "%s" '
            'with field number %d.' %
            (extension.full_name, existing_desc.full_name,
             extension.containing_type.full_name, extension.number))

    self._extensions_by_number[extension.containing_type][
        extension.number] = extension
    self._extensions_by_name[extension.containing_type][
        extension.full_name] = extension

    # Also register MessageSet extensions with the type name.
    if _IsMessageSetExtension(extension):
      self._extensions_by_name[extension.containing_type][
          extension.message_type.full_name] = extension