diff options
Diffstat (limited to 'Doc/library/itertools.rst')
| -rw-r--r-- | Doc/library/itertools.rst | 38 |
1 files changed, 30 insertions, 8 deletions
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst index f489535c53..8c7592d17e 100644 --- a/Doc/library/itertools.rst +++ b/Doc/library/itertools.rst @@ -87,10 +87,15 @@ loops that truncate the stream. .. function:: accumulate(iterable[, func]) - Make an iterator that returns accumulated sums. Elements may be any addable - type including :class:`~decimal.Decimal` or :class:`~fractions.Fraction`. - If the optional *func* argument is supplied, it should be a function of two - arguments and it will be used instead of addition. + Make an iterator that returns accumulated sums, or accumulated + results of other binary functions (specified via the optional + *func* argument). If *func* is supplied, it should be a function + of two arguments. Elements of the input *iterable* may be any type + that can be accepted as arguments to *func*. (For example, with + the default operation of addition, elements may be any addable + type including :class:`~decimal.Decimal` or + :class:`~fractions.Fraction`.) If the input iterable is empty, the + output iterable will also be empty. Equivalent to:: @@ -99,7 +104,10 @@ loops that truncate the stream. # accumulate([1,2,3,4,5]) --> 1 3 6 10 15 # accumulate([1,2,3,4,5], operator.mul) --> 1 2 6 24 120 it = iter(iterable) - total = next(it) + try: + total = next(it) + except StopIteration: + return yield total for element in it: total = func(total, element) @@ -400,7 +408,10 @@ loops that truncate the stream. def _grouper(self, tgtkey): while self.currkey == tgtkey: yield self.currvalue - self.currvalue = next(self.it) # Exit on StopIteration + try: + self.currvalue = next(self.it) + except StopIteration: + return self.currkey = self.keyfunc(self.currvalue) @@ -424,7 +435,10 @@ loops that truncate the stream. # islice('ABCDEFG', 0, None, 2) --> A C E G s = slice(*args) it = iter(range(s.start or 0, s.stop or sys.maxsize, s.step or 1)) - nexti = next(it) + try: + nexti = next(it) + except StopIteration: + return for i, element in enumerate(iterable): if i == nexti: yield element @@ -582,7 +596,10 @@ loops that truncate the stream. def gen(mydeque): while True: if not mydeque: # when the local deque is empty - newval = next(it) # fetch a new value and + try: + newval = next(it) # fetch a new value and + except StopIteration: + return for d in deques: # load it to all the deques d.append(newval) yield mydeque.popleft() @@ -657,6 +674,11 @@ which incur interpreter overhead. "Return function(0), function(1), ..." return map(function, count(start)) + def tail(n, iterable): + "Return an iterator over the last n items" + # tail(3, 'ABCDEFG') --> E F G + return iter(collections.deque(iterable, maxlen=n)) + def consume(iterator, n): "Advance the iterator n-steps ahead. If n is none, consume entirely." # Use functions that consume iterators at C speed. |