"""
Plain Python definition of the builtin functions oriented towards
functional programming.
"""

# ____________________________________________________________

def sorted(iterable, key=None, reverse=False):
    "sorted(iterable, key=None, reverse=False) --> new sorted list"
    sorted_lst = list(iterable)
    sorted_lst.sort(key=key, reverse=reverse)
    return sorted_lst

def any(seq):
    """any(iterable) -> bool

Return True if bool(x) is True for any x in the iterable."""
    for x in seq:
        if x:
            return True
    return False

def all(seq):
    """all(iterable) -> bool

Return True if bool(x) is True for all values x in the iterable."""
    for x in seq:
        if not x:
            return False
    return True

def sum(sequence, start=0):
    """sum(sequence[, start]) -> value

Returns the sum of a sequence of numbers (NOT strings) plus the value
of parameter 'start' (which defaults to 0).  When the sequence is
empty, returns start."""
    if isinstance(start, str):
        raise TypeError("sum() can't sum strings [use ''.join(seq) instead]")
    if isinstance(start, bytes):
        raise TypeError("sum() can't sum bytes [use b''.join(seq) instead]")
    if isinstance(start, bytearray):
        raise TypeError("sum() can't sum bytearray [use b''.join(seq) instead]")
    last = start
    for x in sequence:
        # Very intentionally *not* +=, that would have different semantics if
        # start was a mutable type, such as a list
        last = last + x
    return last

def filter(func, seq):
    """filter(function or None, sequence) -> list, tuple, or string

Return those items of sequence for which function(item) is true.  If
function is None, return the items that are true.  If sequence is a tuple
or string, return the same type, else return a list."""
    if func is None:
        func = bool
    return _filter(func, iter(seq))

def _filter(func, iterator):
    for item in iterator:
        if func(item):
            yield item