code: def get_account_alias(env):
    
    env_valid(env)
    # Env is a global env of the form "env.<account_alias>" (e.g. "mgmt.<account_alias>")
    if env.find(".") > -1:
      base, ext = env.split(".")
      return ext
    # Ordinary env, possibly a proto env ending with a digit that is stripped to look up the alias
    else:
      env_short = env.strip(".0123456789")
      if env_short not in EFConfig.ENV_ACCOUNT_MAP:
        raise ValueError("generic env: {} has no entry in ENV_ACCOUNT_MAP of ef_site_config.py".format(env_short))
      return EFConfig.ENV_ACCOUNT_MAP[env_short]
docs: Given an env, return <account_alias> if env is valid
    Args:
      env: an environment, such as "prod", "staging", "proto<N>", "mgmt.<account_alias>"
    Returns:
      the alias of the AWS account that holds the env
    Raises:
      ValueError if env is misformatted or doesn't name a known environment