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class HistoryEmptyException(Exception):
pass
class History(object):
def __init__(self, maxlen = None):
from collections import deque
self.history = deque(maxlen = maxlen)
self.history_forward = deque(maxlen = maxlen)
def add(self, item):
if len(self.history) == 0 or self.history[-1] != item:
self.history.append(item)
self.history_forward.clear()
def __len__(self):
return len(self.history)
def top(self):
try:
return self.history[-1]
except IndexError:
raise HistoryEmptyException()
def bottom(self):
try:
return self.history[0]
except IndexError:
raise HistoryEmptyException()
def back(self):
if len(self.history) > 1:
self.history_forward.append( self.history.pop() )
return self.top()
def move(self, n):
if n > 0:
return self.forward()
if n < 0:
return self.back()
def __iter__(self):
return self.history.__iter__()
def next(self):
return self.history.next()
def forward(self):
if len(self.history_forward) > 0:
self.history.append( self.history_forward.pop() )
return self.top()
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