code: def env(self, key, value=None, unset=False, asap=False):
          
          if unset:
              self._set('unenv', key, multi=True)
          else:
              if value is None:
                  value = os.environ.get(key)
  
              self._set('%senv' % ('i' if asap else ''), '%s=%s' % (key, value), multi=True)
  
          return self
docs: Processes (sets/unsets) environment variable.
  
          If is not given in `set` mode value will be taken from current env.
  
          :param str|unicode key:
  
          :param value:
  
          :param bool unset: Whether to unset this variable.
  
          :param bool asap: If True env variable will be set as soon as possible.