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_pdeque.py
from collections.abc import Sequence, Hashable from itertools import islice, chain from numbers import Integral from pyrsistent._plist import plist class PDeque(object): """ Persistent double ended queue (deque). Allows quick appends and pops in both ends. Implemented using two persistent lists. A maximum length can be specified to create a bounded queue. Fully supports the Sequence and Hashable protocols including indexing and slicing but if you need fast random access go for the PVector instead. Do not instantiate directly, instead use the factory functions :py:func:`dq` or :py:func:`pdeque` to create an instance. Some examples: >>> x = pdeque([1, 2, 3]) >>> x.left 1 >>> x.right 3 >>> x[0] == x.left True >>> x[-1] == x.right True >>> x.pop() pdeque([1, 2]) >>> x.pop() == x[:-1] True >>> x.popleft() pdeque([2, 3]) >>> x.append(4) pdeque([1, 2, 3, 4]) >>> x.appendleft(4) pdeque([4, 1, 2, 3]) >>> y = pdeque([1, 2, 3], maxlen=3) >>> y.append(4) pdeque([2, 3, 4], maxlen=3) >>> y.appendleft(4) pdeque([4, 1, 2], maxlen=3) """ __slots__ = ('_left_list', '_right_list', '_length', '_maxlen', '__weakref__') def __new__(cls, left_list, right_list, length, maxlen=None): instance = super(PDeque, cls).__new__(cls) instance._left_list = left_list instance._right_list = right_list instance._length = length if maxlen is not None: if not isinstance(maxlen, Integral): raise TypeError('An integer is required as maxlen') if maxlen < 0: raise ValueError("maxlen must be non-negative") instance._maxlen = maxlen return instance @property def right(self): """ Rightmost element in dqueue. """ return PDeque._tip_from_lists(self._right_list, self._left_list) @property def left(self): """ Leftmost element in dqueue. """ return PDeque._tip_from_lists(self._left_list, self._right_list) @staticmethod def _tip_from_lists(primary_list, secondary_list): if primary_list: return primary_list.first if secondary_list: return secondary_list[-1] raise IndexError('No elements in empty deque') def __iter__(self): return chain(self._left_list, self._right_list.reverse()) def __repr__(self): return "pdeque({0}{1})".format(list(self), ', maxlen={0}'.format(self._maxlen) if self._maxlen is not None else '') __str__ = __repr__ @property def maxlen(self): """ Maximum length of the queue. """ return self._maxlen def pop(self, count=1): """ Return new deque with rightmost element removed. Popping the empty queue will return the empty queue. A optional count can be given to indicate the number of elements to pop. Popping with a negative index is the same as popleft. Executes in amortized O(k) where k is the number of elements to pop. >>> pdeque([1, 2]).pop() pdeque([1]) >>> pdeque([1, 2]).pop(2) pdeque([]) >>> pdeque([1, 2]).pop(-1) pdeque([2]) """ if count < 0: return self.popleft(-count) new_right_list, new_left_list = PDeque._pop_lists(self._right_list, self._left_list, count) return PDeque(new_left_list, new_right_list, max(self._length - count, 0), self._maxlen) def popleft(self, count=1): """ Return new deque with leftmost element removed. Otherwise functionally equivalent to pop(). >>> pdeque([1, 2]).popleft() pdeque([2]) """ if count < 0: return self.pop(-count) new_left_list, new_right_list = PDeque._pop_lists(self._left_list, self._right_list, count) return PDeque(new_left_list, new_right_list, max(self._length - count, 0), self._maxlen) @staticmethod def _pop_lists(primary_list, secondary_list, count): new_primary_list = primary_list new_secondary_list = secondary_list while count > 0 and (new_primary_list or new_secondary_list): count -= 1 if new_primary_list.rest: new_primary_list = new_primary_list.rest elif new_primary_list: new_primary_list = new_secondary_list.reverse() new_secondary_list = plist() else: new_primary_list = new_secondary_list.reverse().rest new_secondary_list = plist() return new_primary_list, new_secondary_list def _is_empty(self): return not self._left_list and not self._right_list def __lt__(self, other): if not isinstance(other, PDeque): return NotImplemented return tuple(self) < tuple(other) def __eq__(self, other): if not isinstance(other, PDeque): return NotImplemented if tuple(self) == tuple(other): # Sanity check of the length value since it is redundant (there for performance) assert len(self) == len(other) return True return False def __hash__(self): return hash(tuple(self)) def __len__(self): return self._length def append(self, elem): """ Return new deque with elem as the rightmost element. >>> pdeque([1, 2]).append(3) pdeque([1, 2, 3]) """ new_left_list, new_right_list, new_length = self._append(self._left_list, self._right_list, elem) return PDeque(new_left_list, new_right_list, new_length, self._maxlen) def appendleft(self, elem): """ Return new deque with elem as the leftmost element. >>> pdeque([1, 2]).appendleft(3) pdeque([3, 1, 2]) """ new_right_list, new_left_list, new_length = self._append(self._right_list, self._left_list, elem) return PDeque(new_left_list, new_right_list, new_length, self._maxlen) def _append(self, primary_list, secondary_list, elem): if self._maxlen is not None and self._length == self._maxlen: if self._maxlen == 0: return primary_list, secondary_list, 0 new_primary_list, new_secondary_list = PDeque._pop_lists(primary_list, secondary_list, 1) return new_primary_list, new_secondary_list.cons(elem), self._length return primary_list, secondary_list.cons(elem), self._length + 1 @staticmethod def _extend_list(the_list, iterable): count = 0 for elem in iterable: the_list = the_list.cons(elem) count += 1 return the_list, count def _extend(self, primary_list, secondary_list, iterable): new_primary_list, extend_count = PDeque._extend_list(primary_list, iterable) new_secondary_list = secondary_list current_len = self._length + extend_count if self._maxlen is not None and current_len > self._maxlen: pop_len = current_len - self._maxlen new_secondary_list, new_primary_list = PDeque._pop_lists(new_secondary_list, new_primary_list, pop_len) extend_count -= pop_len return new_primary_list, new_secondary_list, extend_count def extend(self, iterable): """ Return new deque with all elements of iterable appended to the right. >>> pdeque([1, 2]).extend([3, 4]) pdeque([1, 2, 3, 4]) """ new_right_list, new_left_list, extend_count = self._extend(self._right_list, self._left_list, iterable) return PDeque(new_left_list, new_right_list, self._length + extend_count, self._maxlen) def extendleft(self, iterable): """ Return new deque with all elements of iterable appended to the left. NB! The elements will be inserted in reverse order compared to the order in the iterable. >>> pdeque([1, 2]).extendleft([3, 4]) pdeque([4, 3, 1, 2]) """ new_left_list, new_right_list, extend_count = self._extend(self._left_list, self._right_list, iterable) return PDeque(new_left_list, new_right_list, self._length + extend_count, self._maxlen) def count(self, elem): """ Return the number of elements equal to elem present in the queue >>> pdeque([1, 2, 1]).count(1) 2 """ return self._left_list.count(elem) + self._right_list.count(elem) def remove(self, elem): """ Return new deque with first element from left equal to elem removed. If no such element is found a ValueError is raised. >>> pdeque([2, 1, 2]).remove(2) pdeque([1, 2]) """ try: return PDeque(self._left_list.remove(elem), self._right_list, self._length - 1) except ValueError: # Value not found in left list, try the right list try: # This is severely inefficient with a double reverse, should perhaps implement a remove_last()? return PDeque(self._left_list, self._right_list.reverse().remove(elem).reverse(), self._length - 1) except ValueError as e: raise ValueError('{0} not found in PDeque'.format(elem)) from e def reverse(self): """ Return reversed deque. >>> pdeque([1, 2, 3]).reverse() pdeque([3, 2, 1]) Also supports the standard python reverse function. >>> reversed(pdeque([1, 2, 3])) pdeque([3, 2, 1]) """ return PDeque(self._right_list, self._left_list, self._length) __reversed__ = reverse def rotate(self, steps): """ Return deque with elements rotated steps steps. >>> x = pdeque([1, 2, 3]) >>> x.rotate(1) pdeque([3, 1, 2]) >>> x.rotate(-2) pdeque([3, 1, 2]) """ popped_deque = self.pop(steps) if steps >= 0: return popped_deque.extendleft(islice(self.reverse(), steps)) return popped_deque.extend(islice(self, -steps)) def __reduce__(self): # Pickling support return pdeque, (list(self), self._maxlen) def __getitem__(self, index): if isinstance(index, slice): if index.step is not None and index.step != 1: # Too difficult, no structural sharing possible return pdeque(tuple(self)[index], maxlen=self._maxlen) result = self if index.start is not None: result = result.popleft(index.start % self._length) if index.stop is not None: result = result.pop(self._length - (index.stop % self._length)) return result if not isinstance(index, Integral): raise TypeError("'%s' object cannot be interpreted as an index" % type(index).__name__) if index >= 0: return self.popleft(index).left shifted = len(self) + index if shifted < 0: raise IndexError( "pdeque index {0} out of range {1}".format(index, len(self)), ) return self.popleft(shifted).left index = Sequence.index Sequence.register(PDeque) Hashable.register(PDeque) def pdeque(iterable=(), maxlen=None): """ Return deque containing the elements of iterable. If maxlen is specified then len(iterable) - maxlen elements are discarded from the left to if len(iterable) > maxlen. >>> pdeque([1, 2, 3]) pdeque([1, 2, 3]) >>> pdeque([1, 2, 3, 4], maxlen=2) pdeque([3, 4], maxlen=2) """ t = tuple(iterable) if maxlen is not None: t = t[-maxlen:] length = len(t) pivot = int(length / 2) left = plist(t[:pivot]) right = plist(t[pivot:], reverse=True) return PDeque(left, right, length, maxlen) def dq(*elements): """ Return deque containing all arguments. >>> dq(1, 2, 3) pdeque([1, 2, 3]) """ return pdeque(elements)
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