old_contents: # -*- coding: utf-8 -*-
  
  """
  @author: Seva Zhidkov
  @contact: zhidkovseva@gmail.com
  @license: The MIT license
  
  Copyright (C) 2015
  """
  
  import os
  
  
  class Config:
      def __init__(self, prefix='SHELDON_'):
          """
          Load config from environment variables.
  
          :param prefix: string, all needed environment variables
                              starts from it.
                              Default - 'SHELDON_'. So, environment
                              variables will be looking like:
                              'SHELDON_BOT_NAME', 'SHELDON_TWITTER_KEY'
          :return:
          """
          # Bot config variables
          self.variables = {}
  
          for variable in os.environ:
              if variable.startswith(prefix):
                  self.variables[variable] = os.environ[variable]
  
      def get(self, variable, default_value):
          """
  
          :param variable: string, needed variable
          :param default_value: string, value that returns if
                                variable is not set
          :return:
          """
          if variable not in self.variables:
              return default_value
  
          return self.variables[variable]
  
  
new_contents: # -*- coding: utf-8 -*-
  
  """
  @author: Seva Zhidkov
  @contact: zhidkovseva@gmail.com
  @license: The MIT license
  
  Copyright (C) 2015
  """
  
  import os
  
  
  class Config:
      def __init__(self, prefix='SHELDON_'):
          """
          Load config from environment variables.
  
          :param prefix: string, all needed environment variables
                              starts from it.
                              Default - 'SHELDON_'. So, environment
                              variables will be looking like:
                              'SHELDON_BOT_NAME', 'SHELDON_TWITTER_KEY'
          :return:
          """
          # Bot config variables
          self.variables = {}
  
          for variable in os.environ:
              if variable.startswith(prefix):
                  self.variables[variable] = os.environ[variable]
  
      def get(self, variable, default_value):
          """
          Get variable value from environment
  
          :param variable: string, needed variable
          :param default_value: string, value that returns if
                                variable is not set
          :return: variable value
          """
          if variable not in self.variables:
              return default_value
  
          return self.variables[variable]
  
      def get_installed_plugins(self):
          """
          Return list of installed plugins from installed_plugins.txt
          :return: list of strings with names of plugins
          """
          plugins_file = open('installed_plugins.txt')
          return plugins_file.readlines()
  
  
subject: Add function for getting installed plugins