Edit

[EDIT] FILE: persistent.py

"""Persistent Data Types
"""

import operator as op
from collections import OrderedDict
from collections.abc import (
    ItemsView,
    KeysView,
    MutableMapping,
    Sequence,
    ValuesView,
)
from contextlib import contextmanager
from shutil import rmtree

from .core import ENOVAL, Cache

def _make_compare(seq_op, doc):
    """Make compare method with Sequence semantics."""

def compare(self, that):
        """Compare method for deque and sequence."""
        if not isinstance(that, Sequence):
            return NotImplemented

len_self = len(self)
        len_that = len(that)

if len_self != len_that:
            if seq_op is op.eq:
                return False
            if seq_op is op.ne:
                return True

for alpha, beta in zip(self, that):
            if alpha != beta:
                return seq_op(alpha, beta)

return seq_op(len_self, len_that)

compare.__name__ = '__{0}__'.format(seq_op.__name__)
    doc_str = 'Return True if and only if deque is {0} `that`.'
    compare.__doc__ = doc_str.format(doc)

return compare

class Deque(Sequence):
    """Persistent sequence with double-ended queue semantics.

Double-ended queue is an ordered collection with optimized access at its
    endpoints.

Items are serialized to disk. Deque may be initialized from directory path
    where items are stored.

>>> deque = Deque()
    >>> deque += range(5)
    >>> list(deque)
    [0, 1, 2, 3, 4]
    >>> for value in range(5):
    ...     deque.appendleft(-value)
    >>> len(deque)
    10
    >>> list(deque)
    [-4, -3, -2, -1, 0, 0, 1, 2, 3, 4]
    >>> deque.pop()
    4
    >>> deque.popleft()
    -4
    >>> deque.reverse()
    >>> list(deque)
    [3, 2, 1, 0, 0, -1, -2, -3]

"""

def __init__(self, iterable=(), directory=None, maxlen=None):
        """Initialize deque instance.

If directory is None then temporary directory created. The directory
        will *not* be automatically removed.

:param iterable: iterable of items to append to deque
        :param directory: deque directory (default None)

"""
        self._cache = Cache(directory, eviction_policy='none')
        self._maxlen = float('inf') if maxlen is None else maxlen
        self._extend(iterable)

@classmethod
    def fromcache(cls, cache, iterable=(), maxlen=None):
        """Initialize deque using `cache`.

>>> cache = Cache()
        >>> deque = Deque.fromcache(cache, [5, 6, 7, 8])
        >>> deque.cache is cache
        True
        >>> len(deque)
        4
        >>> 7 in deque
        True
        >>> deque.popleft()
        5

:param Cache cache: cache to use
        :param iterable: iterable of items
        :return: initialized Deque

"""
        # pylint: disable=no-member,protected-access
        self = cls.__new__(cls)
        self._cache = cache
        self._maxlen = float('inf') if maxlen is None else maxlen
        self._extend(iterable)
        return self

@property
    def cache(self):
        """Cache used by deque."""
        return self._cache

@property
    def directory(self):
        """Directory path where deque is stored."""
        return self._cache.directory

@property
    def maxlen(self):
        """Max length of the deque."""
        return self._maxlen

@maxlen.setter
    def maxlen(self, value):
        """Set max length of the deque.

Pops items from left while length greater than max.

>>> deque = Deque()
        >>> deque.extendleft('abcde')
        >>> deque.maxlen = 3
        >>> list(deque)
        ['c', 'd', 'e']

:param value: max length

"""
        self._maxlen = value
        with self._cache.transact(retry=True):
            while len(self._cache) > self._maxlen:
                self._popleft()

def _index(self, index, func):
        len_self = len(self)

if index >= 0:
            if index >= len_self:
                raise IndexError('deque index out of range')

for key in self._cache.iterkeys():
                if index == 0:
                    try:
                        return func(key)
                    except KeyError:
                        continue
                index -= 1
        else:
            if index < -len_self:
                raise IndexError('deque index out of range')

index += 1

for key in self._cache.iterkeys(reverse=True):
                if index == 0:
                    try:
                        return func(key)
                    except KeyError:
                        continue
                index += 1

raise IndexError('deque index out of range')

def __getitem__(self, index):
        """deque.__getitem__(index) <==> deque[index]

Return corresponding item for `index` in deque.

See also `Deque.peekleft` and `Deque.peek` for indexing deque at index
        ``0`` or ``-1``.

>>> deque = Deque()
        >>> deque.extend('abcde')
        >>> deque[1]
        'b'
        >>> deque[-2]
        'd'

:param int index: index of item
        :return: corresponding item
        :raises IndexError: if index out of range

"""
        return self._index(index, self._cache.__getitem__)

def __setitem__(self, index, value):
        """deque.__setitem__(index, value) <==> deque[index] = value

Store `value` in deque at `index`.

>>> deque = Deque()
        >>> deque.extend([None] * 3)
        >>> deque[0] = 'a'
        >>> deque[1] = 'b'
        >>> deque[-1] = 'c'
        >>> ''.join(deque)
        'abc'

:param int index: index of value
        :param value: value to store
        :raises IndexError: if index out of range

"""

def _set_value(key):
            return self._cache.__setitem__(key, value)

self._index(index, _set_value)

def __delitem__(self, index):
        """deque.__delitem__(index) <==> del deque[index]

Delete item in deque at `index`.

>>> deque = Deque()
        >>> deque.extend([None] * 3)
        >>> del deque[0]
        >>> del deque[1]
        >>> del deque[-1]
        >>> len(deque)
        0

:param int index: index of item
        :raises IndexError: if index out of range

"""
        self._index(index, self._cache.__delitem__)

def __repr__(self):
        """deque.__repr__() <==> repr(deque)

Return string with printable representation of deque.

"""
        name = type(self).__name__
        return '{0}(directory={1!r})'.format(name, self.directory)

__eq__ = _make_compare(op.eq, 'equal to')
    __ne__ = _make_compare(op.ne, 'not equal to')
    __lt__ = _make_compare(op.lt, 'less than')
    __gt__ = _make_compare(op.gt, 'greater than')
    __le__ = _make_compare(op.le, 'less than or equal to')
    __ge__ = _make_compare(op.ge, 'greater than or equal to')

def __iadd__(self, iterable):
        """deque.__iadd__(iterable) <==> deque += iterable

Extend back side of deque with items from iterable.

:param iterable: iterable of items to append to deque
        :return: deque with added items

"""
        self._extend(iterable)
        return self

def __iter__(self):
        """deque.__iter__() <==> iter(deque)

Return iterator of deque from front to back.

"""
        _cache = self._cache

for key in _cache.iterkeys():
            try:
                yield _cache[key]
            except KeyError:
                pass

def __len__(self):
        """deque.__len__() <==> len(deque)

Return length of deque.

"""
        return len(self._cache)

def __reversed__(self):
        """deque.__reversed__() <==> reversed(deque)

Return iterator of deque from back to front.

>>> deque = Deque()
        >>> deque.extend('abcd')
        >>> iterator = reversed(deque)
        >>> next(iterator)
        'd'
        >>> list(iterator)
        ['c', 'b', 'a']

"""
        _cache = self._cache

for key in _cache.iterkeys(reverse=True):
            try:
                yield _cache[key]
            except KeyError:
                pass

def __getstate__(self):
        return self.directory, self.maxlen

def __setstate__(self, state):
        directory, maxlen = state
        self.__init__(directory=directory, maxlen=maxlen)

def append(self, value):
        """Add `value` to back of deque.

>>> deque = Deque()
        >>> deque.append('a')
        >>> deque.append('b')
        >>> deque.append('c')
        >>> list(deque)
        ['a', 'b', 'c']

:param value: value to add to back of deque

"""
        with self._cache.transact(retry=True):
            self._cache.push(value, retry=True)
            if len(self._cache) > self._maxlen:
                self._popleft()

_append = append

def appendleft(self, value):
        """Add `value` to front of deque.

>>> deque = Deque()
        >>> deque.appendleft('a')
        >>> deque.appendleft('b')
        >>> deque.appendleft('c')
        >>> list(deque)
        ['c', 'b', 'a']

:param value: value to add to front of deque

"""
        with self._cache.transact(retry=True):
            self._cache.push(value, side='front', retry=True)
            if len(self._cache) > self._maxlen:
                self._pop()

_appendleft = appendleft

def clear(self):
        """Remove all elements from deque.

>>> deque = Deque('abc')
        >>> len(deque)
        3
        >>> deque.clear()
        >>> list(deque)
        []

"""
        self._cache.clear(retry=True)

_clear = clear

def copy(self):
        """Copy deque with same directory and max length."""
        TypeSelf = type(self)
        return TypeSelf(directory=self.directory, maxlen=self.maxlen)

def count(self, value):
        """Return number of occurrences of `value` in deque.

>>> deque = Deque()
        >>> deque += [num for num in range(1, 5) for _ in range(num)]
        >>> deque.count(0)
        0
        >>> deque.count(1)
        1
        >>> deque.count(4)
        4

:param value: value to count in deque
        :return: count of items equal to value in deque

"""
        return sum(1 for item in self if value == item)

def extend(self, iterable):
        """Extend back side of deque with values from `iterable`.

:param iterable: iterable of values

"""
        for value in iterable:
            self._append(value)

_extend = extend

def extendleft(self, iterable):
        """Extend front side of deque with value from `iterable`.

>>> deque = Deque()
        >>> deque.extendleft('abc')
        >>> list(deque)
        ['c', 'b', 'a']

:param iterable: iterable of values

"""
        for value in iterable:
            self._appendleft(value)

def peek(self):
        """Peek at value at back of deque.

Faster than indexing deque at -1.

If deque is empty then raise IndexError.

>>> deque = Deque()
        >>> deque.peek()
        Traceback (most recent call last):
            ...
        IndexError: peek from an empty deque
        >>> deque += 'abc'
        >>> deque.peek()
        'c'

:return: value at back of deque
        :raises IndexError: if deque is empty

"""
        default = None, ENOVAL
        _, value = self._cache.peek(default=default, side='back', retry=True)
        if value is ENOVAL:
            raise IndexError('peek from an empty deque')
        return value

def peekleft(self):
        """Peek at value at front of deque.

Faster than indexing deque at 0.

If deque is empty then raise IndexError.

>>> deque = Deque()
        >>> deque.peekleft()
        Traceback (most recent call last):
            ...
        IndexError: peek from an empty deque
        >>> deque += 'abc'
        >>> deque.peekleft()
        'a'

:return: value at front of deque
        :raises IndexError: if deque is empty

"""
        default = None, ENOVAL
        _, value = self._cache.peek(default=default, side='front', retry=True)
        if value is ENOVAL:
            raise IndexError('peek from an empty deque')
        return value

def pop(self):
        """Remove and return value at back of deque.

If deque is empty then raise IndexError.

>>> deque = Deque()
        >>> deque += 'ab'
        >>> deque.pop()
        'b'
        >>> deque.pop()
        'a'
        >>> deque.pop()
        Traceback (most recent call last):
            ...
        IndexError: pop from an empty deque

:return: value at back of deque
        :raises IndexError: if deque is empty

"""
        default = None, ENOVAL
        _, value = self._cache.pull(default=default, side='back', retry=True)
        if value is ENOVAL:
            raise IndexError('pop from an empty deque')
        return value

_pop = pop

def popleft(self):
        """Remove and return value at front of deque.

>>> deque = Deque()
        >>> deque += 'ab'
        >>> deque.popleft()
        'a'
        >>> deque.popleft()
        'b'
        >>> deque.popleft()
        Traceback (most recent call last):
            ...
        IndexError: pop from an empty deque

:return: value at front of deque
        :raises IndexError: if deque is empty

"""
        default = None, ENOVAL
        _, value = self._cache.pull(default=default, retry=True)
        if value is ENOVAL:
            raise IndexError('pop from an empty deque')
        return value

_popleft = popleft

def remove(self, value):
        """Remove first occurrence of `value` in deque.

>>> deque = Deque()
        >>> deque += 'aab'
        >>> deque.remove('a')
        >>> list(deque)
        ['a', 'b']
        >>> deque.remove('b')
        >>> list(deque)
        ['a']
        >>> deque.remove('c')
        Traceback (most recent call last):
            ...
        ValueError: deque.remove(value): value not in deque

:param value: value to remove
        :raises ValueError: if value not in deque

"""
        _cache = self._cache

for key in _cache.iterkeys():
            try:
                item = _cache[key]
            except KeyError:
                continue
            else:
                if value == item:
                    try:
                        del _cache[key]
                    except KeyError:
                        continue
                    return

raise ValueError('deque.remove(value): value not in deque')

def reverse(self):
        """Reverse deque in place.

>>> deque = Deque()
        >>> deque += 'abc'
        >>> deque.reverse()
        >>> list(deque)
        ['c', 'b', 'a']

"""
        # pylint: disable=protected-access
        # GrantJ 2019-03-22 Consider using an algorithm that swaps the values
        # at two keys. Like self._cache.swap(key1, key2, retry=True) The swap
        # method would exchange the values at two given keys. Then, using a
        # forward iterator and a reverse iterator, the reverse method could
        # avoid making copies of the values.
        temp = Deque(iterable=reversed(self))
        self._clear()
        self._extend(temp)
        directory = temp.directory
        temp._cache.close()
        del temp
        rmtree(directory)

def rotate(self, steps=1):
        """Rotate deque right by `steps`.

If steps is negative then rotate left.

>>> deque = Deque()
        >>> deque += range(5)
        >>> deque.rotate(2)
        >>> list(deque)
        [3, 4, 0, 1, 2]
        >>> deque.rotate(-1)
        >>> list(deque)
        [4, 0, 1, 2, 3]

:param int steps: number of steps to rotate (default 1)

"""
        if not isinstance(steps, int):
            type_name = type(steps).__name__
            raise TypeError('integer argument expected, got %s' % type_name)

len_self = len(self)

if not len_self:
            return

if steps >= 0:
            steps %= len_self

for _ in range(steps):
                try:
                    value = self._pop()
                except IndexError:
                    return
                else:
                    self._appendleft(value)
        else:
            steps *= -1
            steps %= len_self

for _ in range(steps):
                try:
                    value = self._popleft()
                except IndexError:
                    return
                else:
                    self._append(value)

__hash__ = None  # type: ignore

@contextmanager
    def transact(self):
        """Context manager to perform a transaction by locking the deque.

While the deque is locked, no other write operation is permitted.
        Transactions should therefore be as short as possible. Read and write
        operations performed in a transaction are atomic. Read operations may
        occur concurrent to a transaction.

Transactions may be nested and may not be shared between threads.

>>> from diskcache import Deque
        >>> deque = Deque()
        >>> deque += range(5)
        >>> with deque.transact():  # Atomically rotate elements.
        ...     value = deque.pop()
        ...     deque.appendleft(value)
        >>> list(deque)
        [4, 0, 1, 2, 3]

:return: context manager for use in `with` statement

"""
        with self._cache.transact(retry=True):
            yield

class Index(MutableMapping):
    """Persistent mutable mapping with insertion order iteration.

Items are serialized to disk. Index may be initialized from directory path
    where items are stored.

Hashing protocol is not used. Keys are looked up by their serialized
    format. See ``diskcache.Disk`` for details.

>>> index = Index()
    >>> index.update([('a', 1), ('b', 2), ('c', 3)])
    >>> index['a']
    1
    >>> list(index)
    ['a', 'b', 'c']
    >>> len(index)
    3
    >>> del index['b']
    >>> index.popitem()
    ('c', 3)

"""

def __init__(self, *args, **kwargs):
        """Initialize index in directory and update items.

Optional first argument may be string specifying directory where items
        are stored. When None or not given, temporary directory is created.

>>> index = Index({'a': 1, 'b': 2, 'c': 3})
        >>> len(index)
        3
        >>> directory = index.directory
        >>> inventory = Index(directory, d=4)
        >>> inventory['b']
        2
        >>> len(inventory)
        4

"""
        if args and isinstance(args[0], (bytes, str)):
            directory = args[0]
            args = args[1:]
        else:
            if args and args[0] is None:
                args = args[1:]
            directory = None
        self._cache = Cache(directory, eviction_policy='none')
        self._update(*args, **kwargs)

_update = MutableMapping.update

@classmethod
    def fromcache(cls, cache, *args, **kwargs):
        """Initialize index using `cache` and update items.

>>> cache = Cache()
        >>> index = Index.fromcache(cache, {'a': 1, 'b': 2, 'c': 3})
        >>> index.cache is cache
        True
        >>> len(index)
        3
        >>> 'b' in index
        True
        >>> index['c']
        3

:param Cache cache: cache to use
        :param args: mapping or sequence of items
        :param kwargs: mapping of items
        :return: initialized Index

"""
        # pylint: disable=no-member,protected-access
        self = cls.__new__(cls)
        self._cache = cache
        self._update(*args, **kwargs)
        return self

@property
    def cache(self):
        """Cache used by index."""
        return self._cache

@property
    def directory(self):
        """Directory path where items are stored."""
        return self._cache.directory

def __getitem__(self, key):
        """index.__getitem__(key) <==> index[key]

Return corresponding value for `key` in index.

>>> index = Index()
        >>> index.update({'a': 1, 'b': 2})
        >>> index['a']
        1
        >>> index['b']
        2
        >>> index['c']
        Traceback (most recent call last):
            ...
        KeyError: 'c'

:param key: key for item
        :return: value for item in index with given key
        :raises KeyError: if key is not found

"""
        return self._cache[key]

def __setitem__(self, key, value):
        """index.__setitem__(key, value) <==> index[key] = value

Set `key` and `value` item in index.

>>> index = Index()
        >>> index['a'] = 1
        >>> index[0] = None
        >>> len(index)
        2

:param key: key for item
        :param value: value for item

"""
        self._cache[key] = value

def __delitem__(self, key):
        """index.__delitem__(key) <==> del index[key]

Delete corresponding item for `key` from index.

>>> index = Index()
        >>> index.update({'a': 1, 'b': 2})
        >>> del index['a']
        >>> del index['b']
        >>> len(index)
        0
        >>> del index['c']
        Traceback (most recent call last):
            ...
        KeyError: 'c'

:param key: key for item
        :raises KeyError: if key is not found

"""
        del self._cache[key]

def setdefault(self, key, default=None):
        """Set and get value for `key` in index using `default`.

If `key` is not in index then set corresponding value to `default`. If
        `key` is in index then ignore `default` and return existing value.

>>> index = Index()
        >>> index.setdefault('a', 0)
        0
        >>> index.setdefault('a', 1)
        0

:param key: key for item
        :param default: value if key is missing (default None)
        :return: value for item in index with given key

"""
        _cache = self._cache
        while True:
            try:
                return _cache[key]
            except KeyError:
                _cache.add(key, default, retry=True)

def peekitem(self, last=True):
        """Peek at key and value item pair in index based on iteration order.

>>> index = Index()
        >>> for num, letter in enumerate('xyz'):
        ...     index[letter] = num
        >>> index.peekitem()
        ('z', 2)
        >>> index.peekitem(last=False)
        ('x', 0)

:param bool last: last item in iteration order (default True)
        :return: key and value item pair
        :raises KeyError: if cache is empty

"""
        return self._cache.peekitem(last, retry=True)

def pop(self, key, default=ENOVAL):
        """Remove corresponding item for `key` from index and return value.

If `key` is missing then return `default`. If `default` is `ENOVAL`
        then raise KeyError.

>>> index = Index({'a': 1, 'b': 2})
        >>> index.pop('a')
        1
        >>> index.pop('b')
        2
        >>> index.pop('c', default=3)
        3
        >>> index.pop('d')
        Traceback (most recent call last):
            ...
        KeyError: 'd'

:param key: key for item
        :param default: return value if key is missing (default ENOVAL)
        :return: value for item if key is found else default
        :raises KeyError: if key is not found and default is ENOVAL

"""
        _cache = self._cache
        value = _cache.pop(key, default=default, retry=True)
        if value is ENOVAL:
            raise KeyError(key)
        return value

def popitem(self, last=True):
        """Remove and return item pair.

Item pairs are returned in last-in-first-out (LIFO) order if last is
        True else first-in-first-out (FIFO) order. LIFO order imitates a stack
        and FIFO order imitates a queue.

>>> index = Index()
        >>> index.update([('a', 1), ('b', 2), ('c', 3)])
        >>> index.popitem()
        ('c', 3)
        >>> index.popitem(last=False)
        ('a', 1)
        >>> index.popitem()
        ('b', 2)
        >>> index.popitem()
        Traceback (most recent call last):
          ...
        KeyError: 'dictionary is empty'

:param bool last: pop last item pair (default True)
        :return: key and value item pair
        :raises KeyError: if index is empty

"""
        # pylint: disable=arguments-differ,unbalanced-tuple-unpacking
        _cache = self._cache

with _cache.transact(retry=True):
            key, value = _cache.peekitem(last=last)
            del _cache[key]

return key, value

def push(self, value, prefix=None, side='back'):
        """Push `value` onto `side` of queue in index identified by `prefix`.

When prefix is None, integer keys are used. Otherwise, string keys are
        used in the format "prefix-integer". Integer starts at 500 trillion.

Defaults to pushing value on back of queue. Set side to 'front' to push
        value on front of queue. Side must be one of 'back' or 'front'.