我终于有时间摆弄这个了。我有点得意忘形了。很长，不过我还是贴吧。我添加了set_item、insert、delete、find和find_left方法，以及一些私有方法，以允许破坏游标抽象的低级操作。我还添加了一个move_cursor方法，该方法会抛出IndexError超出范围或指向非顶级对象的索引元组。
基本上，它（应该）保证只要你只使用公共函数，游标总是指向一个顶层对象，并且插入和删除都发生在顶层。从这里开始，您应该能够安全地实现__getitem__, __setitem__,__delitem__等，甚至可能实现__getslice__, __setslice__。
但是，有一些皱纹。光标始终指向顶级对象的限制使得迭代嵌套列表变得非常容易，就好像它是一个平面列表一样。但这也意味着光标不能指向较低级别的对象，因此某些类型的插入不能insert单独使用。例如，假设您有三个列表：
>>> l1 = [1, 2, 3, 4]
>>> l2 = [5, 6, 7, 8]
>>> l3 = [l1, l2]
>>> l3
[[1, 2, 3, 4], [5, 6, 7, 8]]
现在将这个嵌套结构放入 NLI，移动到5并尝试插入。
>>> nli = NestedListIter(l3)
>>> nli.find(5)
>>> nli.insert(9)
>>> nli.nested_list
[[1, 2, 3, 4], [9, 5, 6, 7, 8]]
如您所见，您可以将某些l2内容插入l3. 事实上，现在要这样做，您必须使用一个私有函数，它以一种令人不快的方式破坏了游标抽象：
>>> nli._insert_at(nli.stack[:-1], 10)
>>> nli.nested_list
[[1, 2, 3, 4], 10, [9, 5, 6, 7, 8]]
>>> nli.get_item()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "nestedlistiterator.py", line 130, in get_item
return self._get_item_at(self.stack)
File "nestedlistiterator.py", line 39, in _get_item_at
item = item[i]
TypeError: 'int' object is unsubscriptable
肯定有一些方法可以实现安全的公共insert_between_branches方法，但它们涉及的复杂性比我现在关心的要多。
当尝试在 之后插入一个值时，会出现另一个问题4。如您所见，您可以在l2before中插入一个值5，但是如果您将光标移动到4and insert，您很快就会意识到您不能在4inside之后插入一些东西l1。
>>> nli.go_to_head()
>>> nli.find(4)
>>> nli.insert(11)
>>> nli.nested_list
[[1, 2, 3, 11, 4], 10, [9, 5, 6, 7, 8]]
从平面访问的角度来看，在 4 之后插入和在 5 之前插入是一回事，但从嵌套列表的角度来看，它们是不同的。由于insert实际上是 a left_insert，因此可以使用right_insert方法部分纠正此问题（反过来，该方法将无法在 l1 的开头插入）。
这些问题可能可以通过允许光标指向较低级别的对象来更普遍地处理，但这会使平面访问更加复杂。简而言之，任何纠正这些问题的尝试都将导致更大的复杂性，无论是在接口的平面侧还是嵌套侧。
（这就是为什么我仍然更喜欢简单enumerate_nested方法的原因！在所有节点（而不仅仅是顶级节点）都有值的适当树结构也可能更简单更好。但是这仍然很有趣。）
import collections
class NestedListIter(object):
'''A mutable container that enables flat traversal of a nested tree of
lists. nested_list should contain only a list-like mutable sequence.
To preserve a clear demarcation between 'leaves' and 'branches', empty
sequences are not allowed as toplevel objects.'''
def __init__(self, nested_list):
if not nested_list:
raise ValueError, 'nested_list must be a non-empty sequence'
self.nested_list = nested_list # at some point, vet this to make sure
self.go_to_head() # it contains no empty sequences
def _is_sequence(self, item=None):
'''Private method to test whether an item is a non-string sequence.
If item is None, test current item.'''
if item is None:
item = self._get_item_at(self.stack)
return isinstance(item, collections.Sequence) and not isinstance(item, basestring)
def _is_in_range(self, index_tuple=None):
'''Private method to test whether an index is in range.
If index is None, test current index.'''
if index_tuple is None:
index_tuple = self.stack
if any(x < 0 for x in index_tuple):
return False
try:
self._get_item_at(index_tuple)
except IndexError:
return False
else:
return True
def _get_item_at(self, index_tuple):
'''Private method to get item at an arbitrary index, with no bounds checking.'''
item = self.nested_list
for i in index_tuple:
item = item[i]
return item
def _set_item_at(self, index_tuple, value):
'''Private method to set item at an arbitrary index, with no bounds checking.
Throws a ValueError if value is an empty non-string sequence.'''
if self._is_sequence(value) and not value:
raise ValueError, "Cannot set an empty list!"
containing_list = self._get_item_at(index_tuple[:-1])
containing_list[index_tuple[-1]] = value
def _insert_at(self, index_tuple, value):
'''Private method to insert item at an arbitrary index, with no bounds checking.
Throws a ValueError if value is an empty non-string sequence.'''
if self._is_sequence(value) and not value:
raise ValueError, "Cannot insert an empty list!"
containing_list = self._get_item_at(index_tuple[:-1])
containing_list.insert(index_tuple[-1], value)
def _delete_at(self, index_tuple):
'''Private method to delete item at an arbitrary index, with no bounds checking.
Recursively deletes a resulting branch of empty lists.'''
containing_list = self._get_item_at(index_tuple[:-1])
del containing_list[index_tuple[-1]]
if not self._get_item_at(index_tuple[:-1]):
self._delete_at(index_tuple[:-1])
def _increment_stack(self):
'''Private method that tires to increment the top value of the stack.
Returns True on success, False on failure (empty stack).'''
try:
self.stack[-1] += 1
except IndexError:
return False
else:
return True
def _decrement_stack(self):
'''Private method that tries to decrement the top value of the stack.
Returns True on success, False on failure (empty stack).'''
try:
self.stack[-1] -= 1
except IndexError:
return False
else:
return True
def go_to_head(self):
'''Move the cursor to the head of the nested list.'''
self.stack = []
while self._is_sequence():
self.stack.append(0)
def go_to_tail(self):
self.stack = []
'''Move the cursor to the tail of the nested list.'''
while self._is_sequence():
self.stack.append(len(self.get_item()) - 1)
def right(self):
'''Move cursor one step right in the nested list.'''
while self._increment_stack() and not self._is_in_range():
self.stack.pop()
if not self.stack:
self.go_to_tail()
return False
while self._is_sequence():
self.stack.append(0)
return True
def left(self):
'''Move cursor one step left in the nested list.'''
while self._decrement_stack() and not self._is_in_range():
self.stack.pop()
if not self.stack:
self.go_to_head()
return False
while self._is_sequence():
self.stack.append(len(self.get_item()) - 1)
return True
def move_cursor(self, index_tuple):
'''Move cursor to the location indicated by index_tuple.
Raises an error if index_tuple is out of range or doesn't correspond
to a toplevel object.'''
item = self._get_item_at(index_tuple)
if self._is_sequence(item):
raise IndexError, 'index_tuple must point to a toplevel object'
def get_item(self):
'''Get the item at the cursor location.'''
return self._get_item_at(self.stack)
def set_item(self, value):
'''Set the item a the cursor locaiton.'''
return self._set_item_at(self.stack, value)
def insert(self, value):
'''Insert an item at the cursor location. If value is a sequence,
cursor moves to the first toplevel object in value after insertion.
Otherwise, cursor does not move.'''
temp_stack = self.stack[:]
self.left()
self._insert_at(temp_stack, value)
self.right()
def delete(self):
'''Deete an item at the cursor location. Cursor does not move.'''
temp_stack = self.stack[:]
self.left()
self._delete_at(temp_stack)
self.right()
def iterate(self):
'''Iterate over the values in nested_list in sequence'''
self.go_to_head()
yield self.get_item()
while self.right():
yield self.get_item()
def iterate_left(self):
'''Iterate over the values in nested_list in reverse.'''
self.go_to_tail()
yield self.get_item()
while self.left():
yield self.get_item()
def find(self, value):
'''Search for value in nested_list; move cursor to first location of value.'''
for i in self.iterate():
if i == value:
break
def find_left(self, value):
'''Search for value backwards in nested_list; move cursor to last location of value.'''
for i in self.iterate_left():
if i == value:
break
def _NLI_Test():
l = [1, 2, 3, ['a', 'b', 'c'], 4, ['d', 'e', [100, 200, 300]], 5, ['a', 'b', 'c'], 6]
nli = NestedListIter(l)
print nli.nested_list
for i in nli.iterate():
print i,
print
for i in nli.iterate_left():
print i,
print
nli.go_to_head()
for i in range(5):
nli.right()
nli.insert('cow')
nli.insert(['c', ['o', 'w']])
print nli.nested_list
nli.find('cow')
print nli.get_item()
nli.delete()
print nli.nested_list
nli.find('c')
nli.delete()
print nli.nested_list
nli.find_left('w')
nli.delete()
nli.find('o')
nli.delete()
print nli.nested_list
print nli.nested_list == l
nli.find(100)
nli.set_item(100.1)
print nli.nested_list
if __name__ == '__main__':
_NLI_Test()