code: def env(cls, separator=None, match=None, whitelist=None, parse_values=None, to_lower=None, convert_underscores=None):
          
          cls.__hierarchy.append(env.Env(separator, match, whitelist, parse_values, to_lower, convert_underscores))
docs: Set environment variables as a source.
  
          By default all environment variables available to the process are used.
          This can be narrowed by the args.
  
          Args:
              separator: Keys are split along this character, the resulting
                  splits are considered nested values.
              match: Regular expression for key matching. Keys matching the
                  expression are considered whitelisted.
              whitelist: Only use environment variables that are listed in this
                  list.
              parse_values: Try to parse all variable for well-known types.
              to_lower: Convert all variable names to lower case.
              convert_underscores: Convert all underscores in the name to dashes,
                  this takes place after separation via the separator option.