"""
List extending automatically to the maximum requested length.
Added indicies are filled with `None` by default.
>>> l = defaultlist()
>>> l
[]
>>> l[2] = "C"
>>> l
[None, None, 'C']
>>> l[4]
>>> l
[None, None, 'C', None, None]
Slices and negative indicies are supported likewise
>>> l[1:4]
[None, 'C', None]
>>> l[-3]
'C'
Simple factory functions can be created via `lambda`.
>>> l = defaultlist(lambda: 'empty')
>>> l[2] = "C"
>>> l[4]
'empty'
>>> l
['empty', 'empty', 'C', 'empty', 'empty']
It is also possible to implement advanced factory functions:
>>> def inc():
... inc.counter += 1
... return inc.counter
>>> inc.counter = -1
>>> l = defaultlist(inc)
>>> l[2] = "C"
>>> l
[0, 1, 'C']
>>> l[4]
4
>>> l
[0, 1, 'C', 3, 4]
Please be aware that these functions are shared between shallow copies of the list.
>>> c = l[1:-1]
>>> c
[1, 'C', 3]
>>> c[5]
7
>>> c
[1, 'C', 3, 5, 6, 7]
>>> l[6]
9
>>> l
[0, 1, 'C', 3, 4, 8, 9]
"""
import sys
__version__ = "1.0.0"
__author__ = 'c0fec0de'
__author_email__ = 'c0fec0de@gmail.com'
__description__ = " collections.defaultdict equivalent implementation of list."
__url__ = "https://github.com/c0fec0de/defaultlist"
[docs]class defaultlist(list):
def __init__(self, factory=None):
"""
List extending automatically to the maximum requested length.
Keyword Args:
factory: Function called for every missing index.
"""
self.__factory = factory or defaultlist.__nonefactory
@staticmethod
def __nonefactory():
return None
def __fill(self, index):
missing = index - len(self) + 1
if missing > 0:
self += [self.__factory() for idx in range(missing)]
def __setitem__(self, index, value):
self.__fill(index)
list.__setitem__(self, index, value)
def __getitem__(self, index):
if isinstance(index, slice):
return self.__getslice(index.start, index.stop, index.step)
else:
self.__fill(index)
return list.__getitem__(self, index)
def __getslice__(self, start, stop, step=None): # pragma: no cover
# python 2.x legacy
if stop == sys.maxint:
stop = None
return self.__getslice(start, stop, step)
def __normidx(self, idx, default):
if idx is None:
idx = default
elif idx < 0:
idx += len(self)
return idx
def __getslice(self, start, stop, step):
end = max((start or 0, stop or 0, 0))
if end:
self.__fill(end)
start = self.__normidx(start, 0)
stop = self.__normidx(stop, len(self))
step = step or 1
r = defaultlist(factory=self.__factory)
for idx in range(start, stop, step):
r.append(list.__getitem__(self, idx))
return r
def __add__(self, other):
if isinstance(other, list):
r = self.copy()
r += other
return r
else:
return list.__add__(self, other)
[docs] def copy(self):
"""Return a shallow copy of the list. Equivalent to a[:]."""
r = defaultlist(factory=self.__factory)
r += self
return r