Source code for xonsh.lib.itertools

from itertools import filterfalse




def as_iterable(iterable_or_scalar):
    """Utility for converting an object to an iterable.
    Parameters
    ----------
    iterable_or_scalar : anything

    Returns
    -------
    l : iterable
        If `obj` was None, return the empty tuple.
        If `obj` was not iterable returns a 1-tuple containing `obj`.
        Otherwise return `obj`

    Notes
    -----
    Although string types are iterable in Python, we are treating them as not iterable in this
    method.  Thus, as_iterable(string) returns (string, )

    Examples
    ---------
    >>> as_iterable(1)
    (1,)
    >>> as_iterable([1, 2, 3])
    [1, 2, 3]
    >>> as_iterable("my string")
    ("my string", )
    """

    if iterable_or_scalar is None:
        return ()
    elif isinstance(iterable_or_scalar, (str, bytes)):
        return (iterable_or_scalar,)
    elif hasattr(iterable_or_scalar, "__iter__"):
        return iterable_or_scalar
    else:
        return (iterable_or_scalar,)





def unique_everseen(iterable, key=None):
    """Yield unique elements, preserving order. Remember all elements ever seen.

    ```
    unique_everseen('AAAABBBCCDAABBB') → A B C D
    unique_everseen('ABBcCAD', str.casefold) → A B c D
    ```

    Source code: https://docs.python.org/3/library/itertools.html#itertools-recipes
    """
    seen = set()
    if key is None:
        for element in filterfalse(seen.__contains__, iterable):
            seen.add(element)
            yield element
    else:
        for element in iterable:
            k = key(element)
            if k not in seen:
                seen.add(k)
                yield element