subtract([iterable-or-mapping]) Elements are subtracted from an iterable or from another mapping (or counter). Like dict.update() but subtracts counts instead of replacing them. Both inputs and outputs may be zero or negative. >>> c = Counter(a=4, b=2, c=0, d=-2) >>> d = Counter(a=1, b=2, c=3, d=4) >>> c.subtract(d) >>> c Counter({'a': 3, 'b': 0, 'c': -3, 'd': -6}) New in version 3.2.

class collections.Counter([iterable-or-mapping]) A Counter is a dict subclass for counting hashable objects. It is an unordered collection where elements are stored as dictionary keys and their counts are stored as dictionary values. Counts are allowed to be any integer value including zero or negative counts. The Counter class is similar to bags or multisets in other languages. Elements are counted from an iterable or initialized from another mapping (or counter): >>> c = Counter()

class collections.abc.Set class collections.abc.MutableSet ABCs for read-only and mutable sets.

new_child(m=None) Returns a new ChainMap containing a new map followed by all of the maps in the current instance. If m is specified, it becomes the new map at the front of the list of mappings; if not specified, an empty dict is used, so that a call to d.new_child() is equivalent to: ChainMap({}, *d.maps). This method is used for creating subcontexts that can be updated without altering values in any of the parent mappings. Changed in version 3.4: The optional m parameter was added.

class collections.abc.ValuesView ABCs for mapping, items, keys, and values views.

maps A user updateable list of mappings. The list is ordered from first-searched to last-searched. It is the only stored state and can be modified to change which mappings are searched. The list should always contain at least one mapping.

class collections.abc.Sized class collections.abc.Callable ABCs for classes that provide respectively the methods __contains__(), __hash__(), __len__(), and __call__().

class collections.ChainMap(*maps) A ChainMap groups multiple dicts or other mappings together to create a single, updateable view. If no maps are specified, a single empty dictionary is provided so that a new chain always has at least one mapping. The underlying mappings are stored in a list. That list is public and can be accessed or updated using the maps attribute. There is no other state. Lookups search the underlying mappings successively until a key is found. In contrast, writes, updat

class collections.abc.Sequence class collections.abc.MutableSequence class collections.abc.ByteString ABCs for read-only and mutable sequences. Implementation note: Some of the mixin methods, such as __iter__(), __reversed__() and index(), make repeated calls to the underlying __getitem__() method. Consequently, if __getitem__() is implemented with constant access speed, the mixin methods will have linear performance; however, if the underlying method is linear (as it would be with a linked l

class collections.abc.MutableSet ABCs for read-only and mutable sets.