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#!/usr/bin/python3
from heapq import heappush, heappop
import itertools
# A simple priority queue based on the heapq class.
class PQueue(object):
REMOVED = '<removed-task>' # placeholder for a removed task
def __init__(self):
self.pq = [] # list of entries arranged in a heap
self.entry_finder = {} # mapping of tasks to entries
self.counter = itertools.count() # unique sequence count
self.size = 0
def push(self, task, priority=0):
'Add a new task or update the priority of an existing task'
if task in self.entry_finder:
self.remove(task)
else:
self.size += 1
entry = [priority, next(self.counter), task]
self.entry_finder[task] = entry
heappush(self.pq, entry)
def remove(self, task):
'Mark an existing task as REMOVED. Raise KeyError if not found.'
entry = self.entry_finder.pop(task)
entry[-1] = self.REMOVED
self.size -= 1
def pop(self):
'Remove and return the lowest priority task. Raise KeyError if empty.'
while self.pq:
priority, count, task = heappop(self.pq)
if task is not self.REMOVED:
del self.entry_finder[task]
self.size -= 1
return task
return None
def __len__(self):
return self.size
# Return [n]th line in [text].
def get_line(text, n):
lines = text.split('\n')
if n >= 0 and n < len(lines):
return lines[n]
return None
# Indent each line in [text] by [indent] spaces.
def indent(text, indent=2):
return '\n'.join([' '*indent+line for line in text.split('\n')])
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