Function iterate

python/pathway/internals/common.py:39–91

Iterate function until fixed point. Function has to take only Table arguments. Function has to return a single Table, a tuple of Tables, or a dict of Tables. Iterate returns the same shape of arguments as the ``func`` function: either a single Table, a tuple of Tables, or a dict of T

(
    func,
    iteration_limit: int | None = None,
    **kwargs: table.Table | op.iterate_universe,
)

@check_arg_types
def iterate(
    func,
    iteration_limit: int | None = None,
    **kwargs: table.Table | op.iterate_universe,
):
    """Iterate function until fixed point.
    Function has to take only Table arguments.
    Function has to return a single Table, a tuple of Tables, or a dict of Tables.
    Iterate returns the same shape of arguments as the ``func`` function:
    either a single Table, a tuple of Tables, or a dict of Tables, respectively.
    Initial arguments to function are passed through kwargs.

    Example:

    >>> import pathway as pw
    >>> def collatz_transformer(iterated):
    ...     @pw.udf(deterministic=True)
    ...     def collatz_step(x: int) -> int:
    ...         if x == 1:
    ...             return 1
    ...         elif x % 2 == 0:
    ...             return x // 2
    ...         else:
    ...             return 3 * x + 1
    ...     return iterated.select(val=collatz_step(iterated.val))
    >>> tab = pw.debug.table_from_markdown('''
    ... val
    ...   1
    ...   2
    ...   3
    ...   4
    ...   5
    ...   6
    ...   7
    ...   8''')
    >>> ret = pw.iterate(collatz_transformer, iterated=tab)
    >>> pw.debug.compute_and_print(ret, include_id=False)
    val
    1
    1
    1
    1
    1
    1
    1
    1
    """
    if iteration_limit is not None and iteration_limit < 1:
        raise ValueError("wrong iteration limit")
    fn_spec = function_spec(func)
    return G.add_iterate(
        fn_spec, lambda node: node(**kwargs), iteration_limit=iteration_limit
    )


@check_arg_types