1、計數器（counter）
Counter是對字典類型的補充，用于追蹤值的出現次數。
ps：具備字典的所有功能 + 自己的功能
?如：
python語言程序設計。c?=?collections.Counter('abcdeabcdabcaba')
print?c
輸出：Counter({'a':?5,?'b':?4,?'c':?3,?'d':?2,?'e':?1})
參數里可以是列表或者遠足也可以
counter原代碼：
######################################################################## ### Counter ########################################################################class Counter(dict):'''Dict subclass for counting hashable items. Sometimes called a bagor multiset. Elements are stored as dictionary keys and their countsare stored as dictionary values.>>> c = Counter('abcdeabcdabcaba') # count elements from a string>>> c.most_common(3) # three most common elements[('a', 5), ('b', 4), ('c', 3)]>>> sorted(c) # list all unique elements['a', 'b', 'c', 'd', 'e']>>> ''.join(sorted(c.elements())) # list elements with repetitions'aaaaabbbbcccdde'>>> sum(c.values()) # total of all counts>>> c['a'] # count of letter 'a'>>> for elem in 'shazam': # update counts from an iterable... c[elem] += 1 # by adding 1 to each element's count>>> c['a'] # now there are seven 'a'>>> del c['b'] # remove all 'b'>>> c['b'] # now there are zero 'b'>>> d = Counter('simsalabim') # make another counter>>> c.update(d) # add in the second counter>>> c['a'] # now there are nine 'a'>>> c.clear() # empty the counter>>> cCounter()Note: If a count is set to zero or reduced to zero, it will remainin the counter until the entry is deleted or the counter is cleared:>>> c = Counter('aaabbc')>>> c['b'] -= 2 # reduce the count of 'b' by two>>> c.most_common() # 'b' is still in, but its count is zero[('a', 3), ('c', 1), ('b', 0)]'''# References:# http://en.wikipedia.org/wiki/Multiset# http://www.gnu.org/software/smalltalk/manual-base/html_node/Bag.html# http://www.demo2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm# http://code.activestate.com/recipes/259174/# Knuth, TAOCP Vol. II section 4.6.3def __init__(self, iterable=None, **kwds):'''Create a new, empty Counter object. And if given, count elementsfrom an input iterable. Or, initialize the count from another mappingof elements to their counts.>>> c = Counter() # a new, empty counter>>> c = Counter('gallahad') # a new counter from an iterable>>> c = Counter({'a': 4, 'b': 2}) # a new counter from a mapping>>> c = Counter(a=4, b=2) # a new counter from keyword args'''super(Counter, self).__init__()self.update(iterable, **kwds)def __missing__(self, key):""" 對于不存在的元素，返回計數器為0 """'The count of elements not in the Counter is zero.'# Needed so that self[missing_item] does not raise KeyErrorreturn 0def most_common(self, n=None):""" 數量從大到寫排列，獲取前N個元素 """'''List the n most common elements and their counts from the mostcommon to the least. If n is None, then list all element counts.>>> Counter('abcdeabcdabcaba').most_common(3)[('a', 5), ('b', 4), ('c', 3)]'''# Emulate Bag.sortedByCount from Smalltalkif n is None:return sorted(self.iteritems(), key=_itemgetter(1), reverse=True)return _heapq.nlargest(n, self.iteritems(), key=_itemgetter(1))def elements(self):""" 計數器中的所有元素，注：此處非所有元素集合，而是包含所有元素集合的迭代器 """'''Iterator over elements repeating each as many times as its count.>>> c = Counter('ABCABC')>>> sorted(c.elements())['A', 'A', 'B', 'B', 'C', 'C']# Knuth's example for prime factors of 1836: 2**2 * 3**3 * 17**1>>> prime_factors = Counter({2: 2, 3: 3, 17: 1})>>> product = 1>>> for factor in prime_factors.elements(): # loop over factors... product *= factor # and multiply them>>> productNote, if an element's count has been set to zero or is a negativenumber, elements() will ignore it.'''# Emulate Bag.do from Smalltalk and Multiset.begin from C++.return _chain.from_iterable(_starmap(_repeat, self.iteritems()))# Override dict methods where necessary @classmethoddef fromkeys(cls, iterable, v=None):# There is no equivalent method for counters because setting v=1# means that no element can have a count greater than one.raise NotImplementedError('Counter.fromkeys() is undefined. Use Counter(iterable) instead.')def update(self, iterable=None, **kwds):""" 更新計數器，其實就是增加；如果原來沒有，則新建，如果有則加一 """'''Like dict.update() but add counts instead of replacing them.Source can be an iterable, a dictionary, or another Counter instance.>>> c = Counter('which')>>> c.update('witch') # add elements from another iterable>>> d = Counter('watch')>>> c.update(d) # add elements from another counter>>> c['h'] # four 'h' in which, witch, and watch'''# The regular dict.update() operation makes no sense here because the# replace behavior results in the some of original untouched counts# being mixed-in with all of the other counts for a mismash that# doesn't have a straight-forward interpretation in most counting# contexts. Instead, we implement straight-addition. Both the inputs# and outputs are allowed to contain zero and negative counts.if iterable is not None:if isinstance(iterable, Mapping):if self:self_get = self.getfor elem, count in iterable.iteritems():self[elem] = self_get(elem, 0) + countelse:super(Counter, self).update(iterable) # fast path when counter is emptyelse:self_get = self.getfor elem in iterable:self[elem] = self_get(elem, 0) + 1if kwds:self.update(kwds)def subtract(self, iterable=None, **kwds):""" 相減，原來的計數器中的每一個元素的數量減去后添加的元素的數量 """'''Like dict.update() but subtracts counts instead of replacing them.Counts can be reduced below zero. Both the inputs and outputs areallowed to contain zero and negative counts.Source can be an iterable, a dictionary, or another Counter instance.>>> c = Counter('which')>>> c.subtract('witch') # subtract elements from another iterable>>> c.subtract(Counter('watch')) # subtract elements from another counter>>> c['h'] # 2 in which, minus 1 in witch, minus 1 in watch>>> c['w'] # 1 in which, minus 1 in witch, minus 1 in watch-1'''if iterable is not None:self_get = self.getif isinstance(iterable, Mapping):for elem, count in iterable.items():self[elem] = self_get(elem, 0) - countelse:for elem in iterable:self[elem] = self_get(elem, 0) - 1if kwds:self.subtract(kwds)def copy(self):""" 拷貝 """'Return a shallow copy.'return self.__class__(self)def __reduce__(self):""" 返回一個元組（類型，元組） """return self.__class__, (dict(self),)def __delitem__(self, elem):""" 刪除元素 """'Like dict.__delitem__() but does not raise KeyError for missing values.'if elem in self:super(Counter, self).__delitem__(elem)def __repr__(self):if not self:return '%s()' % self.__class__.__name__items = ', '.join(map('%r: %r'.__mod__, self.most_common()))return '%s({%s})' % (self.__class__.__name__, items)# Multiset-style mathematical operations discussed in:# Knuth TAOCP Volume II section 4.6.3 exercise 19# and at http://en.wikipedia.org/wiki/Multiset# # Outputs guaranteed to only include positive counts.# # To strip negative and zero counts, add-in an empty counter:# c += Counter()def __add__(self, other):'''Add counts from two counters.>>> Counter('abbb') + Counter('bcc')Counter({'b': 4, 'c': 2, 'a': 1})'''if not isinstance(other, Counter):return NotImplementedresult = Counter()for elem, count in self.items():newcount = count + other[elem]if newcount > 0:result[elem] = newcountfor elem, count in other.items():if elem not in self and count > 0:result[elem] = countreturn resultdef __sub__(self, other):''' Subtract count, but keep only results with positive counts.>>> Counter('abbbc') - Counter('bccd')Counter({'b': 2, 'a': 1})'''if not isinstance(other, Counter):return NotImplementedresult = Counter()for elem, count in self.items():newcount = count - other[elem]if newcount > 0:result[elem] = newcountfor elem, count in other.items():if elem not in self and count < 0:result[elem] = 0 - countreturn resultdef __or__(self, other):'''Union is the maximum of value in either of the input counters.>>> Counter('abbb') | Counter('bcc')Counter({'b': 3, 'c': 2, 'a': 1})'''if not isinstance(other, Counter):return NotImplementedresult = Counter()for elem, count in self.items():other_count = other[elem]newcount = other_count if count < other_count else countif newcount > 0:result[elem] = newcountfor elem, count in other.items():if elem not in self and count > 0:result[elem] = countreturn resultdef __and__(self, other):''' Intersection is the minimum of corresponding counts.>>> Counter('abbb') & Counter('bcc')Counter({'b': 1})'''if not isinstance(other, Counter):return NotImplementedresult = Counter()for elem, count in self.items():other_count = other[elem]newcount = count if count < other_count else other_countif newcount > 0:result[elem] = newcountreturn resultCounter
python有什么用，?
2、有序字典(orderedDict )
orderdDict是對字典類型的補充，他記住了字典元素添加的順序
class OrderedDict(dict):'Dictionary that remembers insertion order'# An inherited dict maps keys to values.# The inherited dict provides __getitem__, __len__, __contains__, and get.# The remaining methods are order-aware.# Big-O running times for all methods are the same as regular dictionaries.# The internal self.__map dict maps keys to links in a doubly linked list.# The circular doubly linked list starts and ends with a sentinel element.# The sentinel element never gets deleted (this simplifies the algorithm).# Each link is stored as a list of length three: [PREV, NEXT, KEY].def __init__(self, *args, **kwds):'''Initialize an ordered dictionary. The signature is the same asregular dictionaries, but keyword arguments are not recommended becausetheir insertion order is arbitrary.'''if len(args) > 1:raise TypeError('expected at most 1 arguments, got %d' % len(args))try:self.__rootexcept AttributeError:self.__root = root = [] # sentinel noderoot[:] = [root, root, None]self.__map = {}self.__update(*args, **kwds)def __setitem__(self, key, value, dict_setitem=dict.__setitem__):'od.__setitem__(i, y) <==> od[i]=y'# Setting a new item creates a new link at the end of the linked list,# and the inherited dictionary is updated with the new key/value pair.if key not in self:root = self.__rootlast = root[0]last[1] = root[0] = self.__map[key] = [last, root, key]return dict_setitem(self, key, value)def __delitem__(self, key, dict_delitem=dict.__delitem__):'od.__delitem__(y) <==> del od[y]'# Deleting an existing item uses self.__map to find the link which gets# removed by updating the links in the predecessor and successor nodes. dict_delitem(self, key)link_prev, link_next, _ = self.__map.pop(key)link_prev[1] = link_next # update link_prev[NEXT]link_next[0] = link_prev # update link_next[PREV]def __iter__(self):'od.__iter__() <==> iter(od)'# Traverse the linked list in order.root = self.__rootcurr = root[1] # start at the first nodewhile curr is not root:yield curr[2] # yield the curr[KEY]curr = curr[1] # move to next nodedef __reversed__(self):'od.__reversed__() <==> reversed(od)'# Traverse the linked list in reverse order.root = self.__rootcurr = root[0] # start at the last nodewhile curr is not root:yield curr[2] # yield the curr[KEY]curr = curr[0] # move to previous nodedef clear(self):'od.clear() -> None. Remove all items from od.'root = self.__rootroot[:] = [root, root, None]self.__map.clear()dict.clear(self)# -- the following methods do not depend on the internal structure --def keys(self):'od.keys() -> list of keys in od'return list(self)def values(self):'od.values() -> list of values in od'return [self[key] for key in self]def items(self):'od.items() -> list of (key, value) pairs in od'return [(key, self[key]) for key in self]def iterkeys(self):'od.iterkeys() -> an iterator over the keys in od'return iter(self)def itervalues(self):'od.itervalues -> an iterator over the values in od'for k in self:yield self[k]def iteritems(self):'od.iteritems -> an iterator over the (key, value) pairs in od'for k in self:yield (k, self[k])update = MutableMapping.update__update = update # let subclasses override update without breaking __init____marker = object()def pop(self, key, default=__marker):'''od.pop(k[,d]) -> v, remove specified key and return the correspondingvalue. If key is not found, d is returned if given, otherwise KeyErroris raised.'''if key in self:result = self[key]del self[key]return resultif default is self.__marker:raise KeyError(key)return defaultdef setdefault(self, key, default=None):'od.setdefault(k[,d]) -> od.get(k,d), also set od[k]=d if k not in od'if key in self:return self[key]self[key] = defaultreturn defaultdef popitem(self, last=True):'''od.popitem() -> (k, v), return and remove a (key, value) pair.Pairs are returned in LIFO order if last is true or FIFO order if false.'''if not self:raise KeyError('dictionary is empty')key = next(reversed(self) if last else iter(self))value = self.pop(key)return key, valuedef __repr__(self, _repr_running={}):'od.__repr__() <==> repr(od)'call_key = id(self), _get_ident()if call_key in _repr_running:return '...'_repr_running[call_key] = 1try:if not self:return '%s()' % (self.__class__.__name__,)return '%s(%r)' % (self.__class__.__name__, self.items())finally:del _repr_running[call_key]def __reduce__(self):'Return state information for pickling'items = [[k, self[k]] for k in self]inst_dict = vars(self).copy()for k in vars(OrderedDict()):inst_dict.pop(k, None)if inst_dict:return (self.__class__, (items,), inst_dict)return self.__class__, (items,)def copy(self):'od.copy() -> a shallow copy of od'return self.__class__(self)@classmethoddef fromkeys(cls, iterable, value=None):'''OD.fromkeys(S[, v]) -> New ordered dictionary with keys from S.If not specified, the value defaults to None.'''self = cls()for key in iterable:self[key] = valuereturn selfdef __eq__(self, other):'''od.__eq__(y) <==> od==y. Comparison to another OD is order-sensitivewhile comparison to a regular mapping is order-insensitive.'''if isinstance(other, OrderedDict):return dict.__eq__(self, other) and all(_imap(_eq, self, other))return dict.__eq__(self, other)def __ne__(self, other):'od.__ne__(y) <==> od!=y'return not self == other# -- the following methods support python 3.x style dictionary views --def viewkeys(self):"od.viewkeys() -> a set-like object providing a view on od's keys"return KeysView(self)def viewvalues(self):"od.viewvalues() -> an object providing a view on od's values"return ValuesView(self)def viewitems(self):"od.viewitems() -> a set-like object providing a view on od's items"return ItemsView(self)OrderedDict
3、默認字典(defaultdict)?
defaultdict是對字典的類型的補充，他默認給字典的值設置了一個類型。
python3，?
4、可命名元組(namedtuple)
根據nametuple可以創建一個包含tuple所有功能以及其他功能的類型。
mytuple = collections.namedtuple('mytuple',['x','y','z'])
new = mytuple(1,2,3)
print new
結果：mytuple(x=1, y=2, z=3)
可得出可命名元組，調用時: new.x , 結果: 1
一般運用在坐標上
5、雙向隊列(deque)
一個線程安全的雙向隊列
python和java、q = collections.deque()
q.append(1)
q.append(2)
print q
結果：deque([1,2])
python collection，q.pop() 結果：2 從右起把2取走
q.popleft() ?從左起把1取走
class deque(object):"""deque([iterable[, maxlen]]) --> deque objectBuild an ordered collection with optimized access from its endpoints."""def append(self, *args, **kwargs): # real signature unknown""" Add an element to the right side of the deque. """passdef appendleft(self, *args, **kwargs): # real signature unknown""" Add an element to the left side of the deque. """passdef clear(self, *args, **kwargs): # real signature unknown""" Remove all elements from the deque. """passdef count(self, value): # real signature unknown; restored from __doc__""" D.count(value) -> integer -- return number of occurrences of value """return 0def extend(self, *args, **kwargs): # real signature unknown""" Extend the right side of the deque with elements from the iterable """passdef extendleft(self, *args, **kwargs): # real signature unknown""" Extend the left side of the deque with elements from the iterable """passdef pop(self, *args, **kwargs): # real signature unknown""" Remove and return the rightmost element. """passdef popleft(self, *args, **kwargs): # real signature unknown""" Remove and return the leftmost element. """passdef remove(self, value): # real signature unknown; restored from __doc__""" D.remove(value) -- remove first occurrence of value. """passdef reverse(self): # real signature unknown; restored from __doc__""" D.reverse() -- reverse *IN PLACE* """passdef rotate(self, *args, **kwargs): # real signature unknown""" Rotate the deque n steps to the right (default n=1). If n is negative, rotates left. """passdef __copy__(self, *args, **kwargs): # real signature unknown""" Return a shallow copy of a deque. """passdef __delitem__(self, y): # real signature unknown; restored from __doc__""" x.__delitem__(y) <==> del x[y] """passdef __eq__(self, y): # real signature unknown; restored from __doc__""" x.__eq__(y) <==> x==y """passdef __getattribute__(self, name): # real signature unknown; restored from __doc__""" x.__getattribute__('name') <==> x.name """passdef __getitem__(self, y): # real signature unknown; restored from __doc__""" x.__getitem__(y) <==> x[y] """passdef __ge__(self, y): # real signature unknown; restored from __doc__""" x.__ge__(y) <==> x>=y """passdef __gt__(self, y): # real signature unknown; restored from __doc__""" x.__gt__(y) <==> x>y """passdef __iadd__(self, y): # real signature unknown; restored from __doc__""" x.__iadd__(y) <==> x+=y """passdef __init__(self, iterable=(), maxlen=None): # known case of _collections.deque.__init__"""deque([iterable[, maxlen]]) --> deque objectBuild an ordered collection with optimized access from its endpoints.# (copied from class doc)"""passdef __iter__(self): # real signature unknown; restored from __doc__""" x.__iter__() <==> iter(x) """passdef __len__(self): # real signature unknown; restored from __doc__""" x.__len__() <==> len(x) """passdef __le__(self, y): # real signature unknown; restored from __doc__""" x.__le__(y) <==> x<=y """passdef __lt__(self, y): # real signature unknown; restored from __doc__""" x.__lt__(y) <==> x<y """pass@staticmethod # known case of __new__def __new__(S, *more): # real signature unknown; restored from __doc__""" T.__new__(S, ...) -> a new object with type S, a subtype of T """passdef __ne__(self, y): # real signature unknown; restored from __doc__""" x.__ne__(y) <==> x!=y """passdef __reduce__(self, *args, **kwargs): # real signature unknown""" Return state information for pickling. """passdef __repr__(self): # real signature unknown; restored from __doc__""" x.__repr__() <==> repr(x) """passdef __reversed__(self): # real signature unknown; restored from __doc__""" D.__reversed__() -- return a reverse iterator over the deque """passdef __setitem__(self, i, y): # real signature unknown; restored from __doc__""" x.__setitem__(i, y) <==> x[i]=y """passdef __sizeof__(self): # real signature unknown; restored from __doc__""" D.__sizeof__() -- size of D in memory, in bytes """passmaxlen = property(lambda self: object(), lambda self, v: None, lambda self: None) # default"""maximum size of a deque or None if unbounded"""__hash__ = Nonedeque
注：既然有雙向隊列，也有單項隊列（先進先出 FIFO ） 使用的是Queue模塊，源代碼如下：
class Queue:"""Create a queue object with a given maximum size.If maxsize is <= 0, the queue size is infinite."""def __init__(self, maxsize=0):self.maxsize = maxsizeself._init(maxsize)# mutex must be held whenever the queue is mutating. All methods# that acquire mutex must release it before returning. mutex# is shared between the three conditions, so acquiring and# releasing the conditions also acquires and releases mutex.self.mutex = _threading.Lock()# Notify not_empty whenever an item is added to the queue; a# thread waiting to get is notified then.self.not_empty = _threading.Condition(self.mutex)# Notify not_full whenever an item is removed from the queue;# a thread waiting to put is notified then.self.not_full = _threading.Condition(self.mutex)# Notify all_tasks_done whenever the number of unfinished tasks# drops to zero; thread waiting to join() is notified to resumeself.all_tasks_done = _threading.Condition(self.mutex)self.unfinished_tasks = 0def task_done(self):"""Indicate that a formerly enqueued task is complete.Used by Queue consumer threads. For each get() used to fetch a task,a subsequent call to task_done() tells the queue that the processingon the task is complete.If a join() is currently blocking, it will resume when all itemshave been processed (meaning that a task_done() call was receivedfor every item that had been put() into the queue).Raises a ValueError if called more times than there were itemsplaced in the queue."""self.all_tasks_done.acquire()try:unfinished = self.unfinished_tasks - 1if unfinished <= 0:if unfinished < 0:raise ValueError('task_done() called too many times')self.all_tasks_done.notify_all()self.unfinished_tasks = unfinishedfinally:self.all_tasks_done.release()def join(self):"""Blocks until all items in the Queue have been gotten and processed.The count of unfinished tasks goes up whenever an item is added to thequeue. The count goes down whenever a consumer thread calls task_done()to indicate the item was retrieved and all work on it is complete.When the count of unfinished tasks drops to zero, join() unblocks."""self.all_tasks_done.acquire()try:while self.unfinished_tasks:self.all_tasks_done.wait()finally:self.all_tasks_done.release()def qsize(self):"""Return the approximate size of the queue (not reliable!)."""self.mutex.acquire()n = self._qsize()self.mutex.release()return ndef empty(self):"""Return True if the queue is empty, False otherwise (not reliable!)."""self.mutex.acquire()n = not self._qsize()self.mutex.release()return ndef full(self):"""Return True if the queue is full, False otherwise (not reliable!)."""self.mutex.acquire()n = 0 < self.maxsize == self._qsize()self.mutex.release()return ndef put(self, item, block=True, timeout=None):"""Put an item into the queue.If optional args 'block' is true and 'timeout' is None (the default),block if necessary until a free slot is available. If 'timeout' isa non-negative number, it blocks at most 'timeout' seconds and raisesthe Full exception if no free slot was available within that time.Otherwise ('block' is false), put an item on the queue if a free slotis immediately available, else raise the Full exception ('timeout'is ignored in that case)."""self.not_full.acquire()try:if self.maxsize > 0:if not block:if self._qsize() == self.maxsize:raise Fullelif timeout is None:while self._qsize() == self.maxsize:self.not_full.wait()elif timeout < 0:raise ValueError("'timeout' must be a non-negative number")else:endtime = _time() + timeoutwhile self._qsize() == self.maxsize:remaining = endtime - _time()if remaining <= 0.0:raise Fullself.not_full.wait(remaining)self._put(item)self.unfinished_tasks += 1self.not_empty.notify()finally:self.not_full.release()def put_nowait(self, item):"""Put an item into the queue without blocking.Only enqueue the item if a free slot is immediately available.Otherwise raise the Full exception."""return self.put(item, False)def get(self, block=True, timeout=None):"""Remove and return an item from the queue.If optional args 'block' is true and 'timeout' is None (the default),block if necessary until an item is available. If 'timeout' isa non-negative number, it blocks at most 'timeout' seconds and raisesthe Empty exception if no item was available within that time.Otherwise ('block' is false), return an item if one is immediatelyavailable, else raise the Empty exception ('timeout' is ignoredin that case)."""self.not_empty.acquire()try:if not block:if not self._qsize():raise Emptyelif timeout is None:while not self._qsize():self.not_empty.wait()elif timeout < 0:raise ValueError("'timeout' must be a non-negative number")else:endtime = _time() + timeoutwhile not self._qsize():remaining = endtime - _time()if remaining <= 0.0:raise Emptyself.not_empty.wait(remaining)item = self._get()self.not_full.notify()return itemfinally:self.not_empty.release()def get_nowait(self):"""Remove and return an item from the queue without blocking.Only get an item if one is immediately available. Otherwiseraise the Empty exception."""return self.get(False)# Override these methods to implement other queue organizations# (e.g. stack or priority queue).# These will only be called with appropriate locks held# Initialize the queue representationdef _init(self, maxsize):self.queue = deque()def _qsize(self, len=len):return len(self.queue)# Put a new item in the queuedef _put(self, item):self.queue.append(item)# Get an item from the queuedef _get(self):return self.queue.popleft()Queue.Queue
?
說到隊列，再提下其和棧的區別：
python中collections模塊，隊列：FIFO(先進先出)
棧：后進先出
?
