$ py -h
usage: py [-x] [-l] [-c PRE_CMD] [-C POST_CMD] [-V] [-h] [expression]

positional arguments:
  expression     e.g. py '2 ** 32'

Options:
  -x             treat each row of stdin as x
  -l             treat list of stdin as l
  -c PRE_CMD     run code before expression
  -C POST_CMD    run code after expression
  -V, --version  version info
  -h, --help     show this help message and exit

Note that -x and -l are mutually exclusive.