code: def _configure_proxy(self):
          
          if os.getenv('HTTP_PROXY') or os.getenv('HTTPS_PROXY'):
              # TODO: is this appropriate?
              # don't change proxy settings if the OS already has them configured.
              return True
  
          proxy_enabled = False
          if self.args.proxy_host is not None and self.args.proxy_port is not None:
              if self.args.proxy_user is not None and self.args.proxy_pass is not None:
                  proxy_user = quote(self.args.proxy_user, safe='~')
                  proxy_pass = quote(self.args.proxy_pass, safe='~')
  
                  # proxy url with auth
                  proxy_url = '{}:{}@{}:{}'.format(
                      proxy_user, proxy_pass, self.args.proxy_host, self.args.proxy_port
                  )
              else:
                  # proxy url without auth
                  proxy_url = '{}:{}'.format(self.args.proxy_host, self.args.proxy_port)
  
              os.putenv('HTTP_PROXY', 'http://{}'.format(proxy_url))
              os.putenv('HTTPS_PROXY', 'https://{}'.format(proxy_url))
  
              print(
                  'Using Proxy Server: {}{}:{}.'.format(
                      c.Fore.CYAN, self.args.proxy_host, self.args.proxy_port
                  )
              )
              proxy_enabled = True
          return proxy_enabled
docs: Configure proxy settings using environment variables.