关于python：使用f.next()迭代时返回多行

rewinding multiple lines when iterating with f.next()

这个问题的后续行动。如何修改此代码以允许重绕多行？

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class rewindable_iterator(object):
not_started = object()

def __init__(self, iterator):
self._iter = iter(iterator)
self._use_save = False
self._save = self.not_started

def __iter__(self):
return self

def next(self):
if self._use_save:
self._use_save = False
else:
self._save = self._iter.next()
return self._save

def backup(self):
if self._use_save:
raise RuntimeError("Tried to backup more than one step.")
elif self._save is self.not_started:
raise RuntimeError("Can't backup past the beginning.")
self._use_save = True

相关讨论

这就是我提出的解决方案：

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from collections import deque
class rewindable_iterator(object):
not_started = object()

def __init__(self, filename,deque_max_length=2):
self._f=open(filename,'r')
self._iter = iter(self._f)
self._use_save = False
# self._use_save2 = False
self._save = self.not_started
self._use_num=0
self._deque=deque([],deque_max_length)

def __iter__(self):
return self
def __enter__(self):
return self
def readline(self):
return self._iter.readline()

def __exit__(self,exc_type, exc_value, traceback):
if exc_type is not None:
print exc_type, exc_value, traceback
self._f.close()

def next(self):
if self._use_save:
self._use_num -= 1
if not self._use_num:
self._use_save = False
return self._deque[-self._use_num-1]
else:
self._save = self._iter.next()
self._deque.append(self._save)
return self._save

def backup(self,num=2):

if self._use_num+num>len(self._deque):
raise RuntimeError("Tried to backup more than the available lines")
elif self._save is self.not_started:
raise RuntimeError("Can't backup past the beginning.")
self._use_save = True
self._use_num+=num