mirror of
https://github.com/ArchiveBox/ArchiveBox
synced 2024-11-10 14:44:18 +00:00
115 lines
3.6 KiB
Python
115 lines
3.6 KiB
Python
from sys import maxsize
|
|
from itertools import islice
|
|
from collections import deque
|
|
|
|
_marker = object()
|
|
|
|
class Peekable(object):
|
|
"""Peekable version of a normal python generator.
|
|
Useful when you don't want to evaluate the entire iterable to look at
|
|
a specific item at a given idx.
|
|
"""
|
|
def __init__(self, iterable):
|
|
self._it = iter(iterable)
|
|
self._cache = deque()
|
|
|
|
def __iter__(self):
|
|
return self
|
|
|
|
def __bool__(self):
|
|
try:
|
|
self.peek()
|
|
except StopIteration:
|
|
return False
|
|
return True
|
|
|
|
def __nonzero__(self):
|
|
# For Python 2 compatibility
|
|
return self.__bool__()
|
|
|
|
def peek(self, default=_marker):
|
|
"""Return the item that will be next returned from ``next()``.
|
|
Return ``default`` if there are no items left. If ``default`` is not
|
|
provided, raise ``StopIteration``.
|
|
"""
|
|
if not self._cache:
|
|
try:
|
|
self._cache.append(next(self._it))
|
|
except StopIteration:
|
|
if default is _marker:
|
|
raise
|
|
return default
|
|
return self._cache[0]
|
|
|
|
def prepend(self, *items):
|
|
"""Stack up items to be the next ones returned from ``next()`` or
|
|
``self.peek()``. The items will be returned in
|
|
first in, first out order::
|
|
>>> p = peekable([1, 2, 3])
|
|
>>> p.prepend(10, 11, 12)
|
|
>>> next(p)
|
|
10
|
|
>>> list(p)
|
|
[11, 12, 1, 2, 3]
|
|
It is possible, by prepending items, to "resurrect" a peekable that
|
|
previously raised ``StopIteration``.
|
|
>>> p = peekable([])
|
|
>>> next(p)
|
|
Traceback (most recent call last):
|
|
...
|
|
StopIteration
|
|
>>> p.prepend(1)
|
|
>>> next(p)
|
|
1
|
|
>>> next(p)
|
|
Traceback (most recent call last):
|
|
...
|
|
StopIteration
|
|
"""
|
|
self._cache.extendleft(reversed(items))
|
|
|
|
def __next__(self):
|
|
if self._cache:
|
|
return self._cache.popleft()
|
|
|
|
return next(self._it)
|
|
|
|
next = __next__ # For Python 2 compatibility
|
|
|
|
def _get_slice(self, index):
|
|
# Normalize the slice's arguments
|
|
step = 1 if (index.step is None) else index.step
|
|
if step > 0:
|
|
start = 0 if (index.start is None) else index.start
|
|
stop = maxsize if (index.stop is None) else index.stop
|
|
elif step < 0:
|
|
start = -1 if (index.start is None) else index.start
|
|
stop = (-maxsize - 1) if (index.stop is None) else index.stop
|
|
else:
|
|
raise ValueError('slice step cannot be zero')
|
|
|
|
# If either the start or stop index is negative, we'll need to cache
|
|
# the rest of the iterable in order to slice from the right side.
|
|
if (start < 0) or (stop < 0):
|
|
self._cache.extend(self._it)
|
|
# Otherwise we'll need to find the rightmost index and cache to that
|
|
# point.
|
|
else:
|
|
n = min(max(start, stop) + 1, maxsize)
|
|
cache_len = len(self._cache)
|
|
if n >= cache_len:
|
|
self._cache.extend(islice(self._it, n - cache_len))
|
|
|
|
return list(self._cache)[index]
|
|
|
|
def __getitem__(self, index):
|
|
if isinstance(index, slice):
|
|
return self._get_slice(index)
|
|
|
|
cache_len = len(self._cache)
|
|
if index < 0:
|
|
self._cache.extend(self._it)
|
|
elif index >= cache_len:
|
|
self._cache.extend(islice(self._it, index + 1 - cache_len))
|
|
|
|
return self._cache[index]
|