old_contents: from itertools import groupby
  from typing import Type, Iterable, List, Dict
  
  from pkg_resources import iter_entry_points
  from httpie.plugins import AuthPlugin, FormatterPlugin, ConverterPlugin
  from httpie.plugins.base import TransportPlugin, BasePlugin
  
  
  ENTRY_POINT_NAMES = [
      'httpie.plugins.auth.v1',
      'httpie.plugins.formatter.v1',
      'httpie.plugins.converter.v1',
      'httpie.plugins.transport.v1',
  ]
  
  
  class PluginManager:
  
      def __init__(self):
          self._plugins = []
  
      def __iter__(self):
          return iter(self._plugins)
  
      def register(self, *plugins: Type[BasePlugin]):
          for plugin in plugins:
              self._plugins.append(plugin)
  
      def unregister(self, plugin: Type[BasePlugin]):
          self._plugins.remove(plugin)
  
      def load_installed_plugins(self):
          for entry_point_name in ENTRY_POINT_NAMES:
              for entry_point in iter_entry_points(entry_point_name):
                  plugin = entry_point.load()
                  plugin.package_name = entry_point.dist.key
                  self.register(entry_point.load())
  
      # Auth
      def get_auth_plugins(self) -> List[Type[AuthPlugin]]:
          return [plugin for plugin in self if issubclass(plugin, AuthPlugin)]
  
      def get_auth_plugin_mapping(self) -> Dict[str, Type[AuthPlugin]]:
          return {
              plugin.auth_type: plugin for plugin in self.get_auth_plugins()
          }
  
      def get_auth_plugin(self, auth_type: str) -> Type[AuthPlugin]:
          return self.get_auth_plugin_mapping()[auth_type]
  
      # Output processing
      def get_formatters(self) -> List[Type[FormatterPlugin]]:
          return [
              plugin for plugin in self
              if issubclass(plugin, FormatterPlugin)
          ]
  
      def get_formatters_grouped(self) -> Dict[str, List[Type[FormatterPlugin]]]:
          groups = {}
          for group_name, group in groupby(
                  self.get_formatters(),
                  key=lambda p: getattr(p, 'group_name', 'format')):
              groups[group_name] = list(group)
          return groups
  
      def get_converters(self) -> List[Type[ConverterPlugin]]:
          return [
              plugin for plugin in self
              if issubclass(plugin, ConverterPlugin)
          ]
  
      # Adapters
      def get_transport_plugins(self) -> List[Type[TransportPlugin]]:
          return [
              plugin for plugin in self
              if issubclass(plugin, TransportPlugin)
          ]
  
new_contents: from itertools import groupby
  from typing import Dict, List, Type
  
  from pkg_resources import iter_entry_points
  
  from httpie.plugins import AuthPlugin, ConverterPlugin, FormatterPlugin
  from httpie.plugins.base import BasePlugin, TransportPlugin
  
  
  ENTRY_POINT_NAMES = [
      'httpie.plugins.auth.v1',
      'httpie.plugins.formatter.v1',
      'httpie.plugins.converter.v1',
      'httpie.plugins.transport.v1',
  ]
  
  
  class PluginManager(list):
  
      def register(self, *plugins: Type[BasePlugin]):
          for plugin in plugins:
              self.append(plugin)
  
      def unregister(self, plugin: Type[BasePlugin]):
          self.remove(plugin)
  
      def filter(self, by_type=Type[BasePlugin]):
          return [plugin for plugin in self if issubclass(plugin, by_type)]
  
      def load_installed_plugins(self):
          for entry_point_name in ENTRY_POINT_NAMES:
              for entry_point in iter_entry_points(entry_point_name):
                  plugin = entry_point.load()
                  plugin.package_name = entry_point.dist.key
                  self.register(entry_point.load())
  
      # Auth
      def get_auth_plugins(self) -> List[Type[AuthPlugin]]:
          return self.filter(AuthPlugin)
  
      def get_auth_plugin_mapping(self) -> Dict[str, Type[AuthPlugin]]:
          return {
              plugin.auth_type: plugin for plugin in self.get_auth_plugins()
          }
  
      def get_auth_plugin(self, auth_type: str) -> Type[AuthPlugin]:
          return self.get_auth_plugin_mapping()[auth_type]
  
      # Output processing
      def get_formatters(self) -> List[Type[FormatterPlugin]]:
          return self.filter(FormatterPlugin)
  
      def get_formatters_grouped(self) -> Dict[str, List[Type[FormatterPlugin]]]:
          groups = {}
          for group_name, group in groupby(
              self.get_formatters(),
              key=lambda p: getattr(p, 'group_name', 'format')):
              groups[group_name] = list(group)
          return groups
  
      def get_converters(self) -> List[Type[ConverterPlugin]]:
          return self.filter(ConverterPlugin)
  
      # Adapters
      def get_transport_plugins(self) -> List[Type[TransportPlugin]]:
          return self.filter(TransportPlugin)
  
      def __repr__(self):
          return f'<PluginManager: {list(self)}>'
  
subject: Refactor `PluginManager`