[utils] Add `LazyList`

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pukkandan 2021-05-28 22:19:13 +05:30
parent c77495e3a4
commit 483336e79e
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@ -3945,6 +3945,56 @@ def detect_exe_version(output, version_re=None, unrecognized='present'):
return unrecognized return unrecognized
class LazyList(collections.Sequence):
''' Lazy immutable list from an iterable
Note that slices of a LazyList are lists and not LazyList'''
def __init__(self, iterable):
self.__iterable = iter(iterable)
self.__cache = []
def __iter__(self):
for item in self.__cache:
yield item
for item in self.__iterable:
self.__cache.append(item)
yield item
def exhaust(self):
''' Evaluate the entire iterable '''
self.__cache.extend(self.__iterable)
def __getitem__(self, idx):
if isinstance(idx, slice):
step = idx.step or 1
start = idx.start if idx.start is not None else 1 if step > 0 else -1
stop = idx.stop if idx.stop is not None else -1 if step > 0 else 0
elif isinstance(idx, int):
start = stop = idx
else:
raise TypeError('indices must be integers or slices')
if start < 0 or stop < 0:
# We need to consume the entire iterable to be able to slice from the end
# Obviously, never use this with infinite iterables
self.exhaust()
else:
n = max(start, stop) - len(self.__cache) + 1
if n > 0:
self.__cache.extend(itertools.islice(self.__iterable, n))
return self.__cache[idx]
def __bool__(self):
try:
self[0]
except IndexError:
return False
return True
def __len__(self):
self.exhaust()
return len(self.__cache)
class PagedList(object): class PagedList(object):
def __len__(self): def __len__(self):
# This is only useful for tests # This is only useful for tests