Function _safe_eval

astroclip/callbacks.py:11–28

Safely evaluate an arithmetic expression. :param s: expression to evaluate; should only contain numbers, spaces, or the symbols `+, -, *, /, _, (, )`; exponential notation is supported :param max_len: maximum length string that will be evaluated; longer strings raise a `Valu

(s: str, max_len: int = 1024)

def _safe_eval(s: str, max_len: int = 1024) -> Union[int, float]:
    """Safely evaluate an arithmetic expression.

    :param s: expression to evaluate; should only contain numbers, spaces, or the
        symbols `+, -, *, /, _, (, )`; exponential notation is supported
    :param max_len: maximum length string that will be evaluated; longer strings raise
        a `ValueError`
    """
    # XXX need to be smarter about this
    is_safe = all(ch in "e0123456789_+-*/(). " for ch in s)
    if not is_safe:
        raise ValueError(
            "Only simple arithmetic expressions involving digits, parentheses, "
            "the letter e, or the symbols '+-*/_.' are allowed"
        )
    if len(s) > max_len:
        raise ValueError(f"String length is {len(s)}, maximum allowed is {max_len}")
    return eval(s)


# allow for the ${eval:...} resolver in the config file to perform simple arithmetic