--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.7/site-packages/boltons/queueutils.py	Sat May 02 07:14:21 2020 -0400
@@ -0,0 +1,194 @@
+# -*- coding: utf-8 -*-
+"""Python comes with a many great data structures, from :class:`dict`
+to :class:`collections.deque`, and no shortage of serviceable
+algorithm implementations, from :func:`sorted` to :mod:`bisect`. But
+priority queues are curiously relegated to an example documented in
+:mod:`heapq`. Even there, the approach presented is not full-featured
+and object-oriented. There is a built-in priority queue,
+:class:`Queue.PriorityQueue`, but in addition to its austere API, it
+carries the double-edged sword of threadsafety, making it fine for
+multi-threaded, multi-consumer applications, but high-overhead for
+cooperative/single-threaded use cases.
+
+The ``queueutils`` module currently provides two Queue
+implementations: :class:`HeapPriorityQueue`, based on a heap, and
+:class:`SortedPriorityQueue`, based on a sorted list. Both use a
+unified API based on :class:`BasePriorityQueue` to facilitate testing
+the slightly different performance characteristics on various
+application use cases.
+
+>>> pq = PriorityQueue()
+>>> pq.add('low priority task', 0)
+>>> pq.add('high priority task', 2)
+>>> pq.add('medium priority task 1', 1)
+>>> pq.add('medium priority task 2', 1)
+>>> len(pq)
+4
+>>> pq.pop()
+'high priority task'
+>>> pq.peek()
+'medium priority task 1'
+>>> len(pq)
+3
+
+"""
+
+
+from heapq import heappush, heappop
+from bisect import insort
+import itertools
+
+try:
+    from typeutils import make_sentinel
+    _REMOVED = make_sentinel(var_name='_REMOVED')
+except ImportError:
+    _REMOVED = object()
+
+try:
+    from listutils import BList
+    # see BarrelList docstring for notes
+except ImportError:
+    BList = list
+
+
+__all__ = ['PriorityQueue', 'BasePriorityQueue',
+           'HeapPriorityQueue', 'SortedPriorityQueue']
+
+
+# TODO: make Base a real abstract class
+# TODO: add uniqueification
+
+
+class BasePriorityQueue(object):
+    """The abstract base class for the other PriorityQueues in this
+    module. Override the ``_backend_type`` class attribute, as well as
+    the :meth:`_push_entry` and :meth:`_pop_entry` staticmethods for
+    custom subclass behavior. (Don't forget to use
+    :func:`staticmethod`).
+
+    Args:
+        priority_key (callable): A function that takes *priority* as
+            passed in by :meth:`add` and returns a real number
+            representing the effective priority.
+
+    """
+    # negating priority means larger numbers = higher priority
+    _default_priority_key = staticmethod(lambda p: -float(p or 0))
+    _backend_type = list
+
+    def __init__(self, **kw):
+        self._pq = self._backend_type()
+        self._entry_map = {}
+        self._counter = itertools.count()
+        self._get_priority = kw.pop('priority_key', self._default_priority_key)
+        if kw:
+            raise TypeError('unexpected keyword arguments: %r' % kw.keys())
+
+    @staticmethod
+    def _push_entry(backend, entry):
+        pass  # abstract
+
+    @staticmethod
+    def _pop_entry(backend):
+        pass  # abstract
+
+    def add(self, task, priority=None):
+        """
+        Add a task to the queue, or change the *task*'s priority if *task*
+        is already in the queue. *task* can be any hashable object,
+        and *priority* defaults to ``0``. Higher values representing
+        higher priority, but this behavior can be controlled by
+        setting *priority_key* in the constructor.
+        """
+        priority = self._get_priority(priority)
+        if task in self._entry_map:
+            self.remove(task)
+        count = next(self._counter)
+        entry = [priority, count, task]
+        self._entry_map[task] = entry
+        self._push_entry(self._pq, entry)
+
+    def remove(self, task):
+        """Remove a task from the priority queue. Raises :exc:`KeyError` if
+        the *task* is absent.
+        """
+        entry = self._entry_map.pop(task)
+        entry[-1] = _REMOVED
+
+    def _cull(self, raise_exc=True):
+        "Remove entries marked as removed by previous :meth:`remove` calls."
+        while self._pq:
+            priority, count, task = self._pq[0]
+            if task is _REMOVED:
+                self._pop_entry(self._pq)
+                continue
+            return
+        if raise_exc:
+            raise IndexError('empty priority queue')
+
+    def peek(self, default=_REMOVED):
+        """Read the next value in the queue without removing it. Returns
+        *default* on an empty queue, or raises :exc:`KeyError` if
+        *default* is not set.
+        """
+        try:
+            self._cull()
+            _, _, task = self._pq[0]
+        except IndexError:
+            if default is not _REMOVED:
+                return default
+            raise IndexError('peek on empty queue')
+        return task
+
+    def pop(self, default=_REMOVED):
+        """Remove and return the next value in the queue. Returns *default* on
+        an empty queue, or raises :exc:`KeyError` if *default* is not
+        set.
+        """
+        try:
+            self._cull()
+            _, _, task = self._pop_entry(self._pq)
+            del self._entry_map[task]
+        except IndexError:
+            if default is not _REMOVED:
+                return default
+            raise IndexError('pop on empty queue')
+        return task
+
+    def __len__(self):
+        "Return the number of tasks in the queue."
+        return len(self._entry_map)
+
+
+class HeapPriorityQueue(BasePriorityQueue):
+    """A priority queue inherited from :class:`BasePriorityQueue`,
+    backed by a list and based on the :func:`heapq.heappop` and
+    :func:`heapq.heappush` functions in the built-in :mod:`heapq`
+    module.
+    """
+    @staticmethod
+    def _pop_entry(backend):
+        return heappop(backend)
+
+    @staticmethod
+    def _push_entry(backend, entry):
+        heappush(backend, entry)
+
+
+class SortedPriorityQueue(BasePriorityQueue):
+    """A priority queue inherited from :class:`BasePriorityQueue`, based
+    on the :func:`bisect.insort` approach for in-order insertion into
+    a sorted list.
+    """
+    _backend_type = BList
+
+    @staticmethod
+    def _pop_entry(backend):
+        return backend.pop(0)
+
+    @staticmethod
+    def _push_entry(backend, entry):
+        insort(backend, entry)
+
+
+PriorityQueue = SortedPriorityQueue