Function arbitrary_element

networkx/utils/misc.py:145–211

Returns an arbitrary element of `iterable` without removing it. This is most useful for "peeking" at an arbitrary element of a set, but can be used for any list, dictionary, etc., as well. Parameters ---------- iterable : `abc.collections.Iterable` instance Any object t

(iterable)

def arbitrary_element(iterable):
    """Returns an arbitrary element of `iterable` without removing it.

    This is most useful for "peeking" at an arbitrary element of a set,
    but can be used for any list, dictionary, etc., as well.

    Parameters
    ----------
    iterable : `abc.collections.Iterable` instance
        Any object that implements ``__iter__``, e.g. set, dict, list, tuple,
        etc.

    Returns
    -------
    The object that results from ``next(iter(iterable))``

    Raises
    ------
    ValueError
        If `iterable` is an iterator (because the current implementation of
        this function would consume an element from the iterator).

    Examples
    --------
    Arbitrary elements from common Iterable objects:

    >>> nx.utils.arbitrary_element([1, 2, 3])  # list
    1
    >>> nx.utils.arbitrary_element((1, 2, 3))  # tuple
    1
    >>> nx.utils.arbitrary_element({1, 2, 3})  # set
    1
    >>> d = {k: v for k, v in zip([1, 2, 3], [3, 2, 1])}
    >>> nx.utils.arbitrary_element(d)  # dict_keys
    1
    >>> nx.utils.arbitrary_element(d.values())  # dict values
    3

    `str` is also an Iterable:

    >>> nx.utils.arbitrary_element("hello")
    'h'

    :exc:`ValueError` is raised if `iterable` is an iterator:

    >>> iterator = iter([1, 2, 3])  # Iterator, *not* Iterable
    >>> nx.utils.arbitrary_element(iterator)
    Traceback (most recent call last):
        ...
    ValueError: cannot return an arbitrary item from an iterator

    Notes
    -----
    This function does not return a *random* element. If `iterable` is
    ordered, sequential calls will return the same value::

        >>> l = [1, 2, 3]
        >>> nx.utils.arbitrary_element(l)