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[Python] comparison of dictionary dict, defaultdict and orderdict

2022-02-01 05:41:44 Hazelnut

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defaultdict

be located collections In module .

Instantiate a defaultdict When , You need to provide a callable object for the constructor , This callable object will be in __getitem__ It is called when it encounters a key that cannot be found , Give Way __getitem__ Return some default value . The callable object used to generate the default value is stored in a file named default_factory In the instance properties of .

Take a chestnut

d = collections.defaultdict(list)		#  An empty dictionary 

d['key']	# []
d.get('key')	# None
 Copy code 

OrderedDict

be located collections In module .

This type will keep the order when adding keys , So the order of key iterations is always the same .

OrderedDict Of popitem Method deletes and returns the last element in the dictionary by default , But if it's like my_odict.popitem(last=False) Call it this way , Then it deletes and returns the first element added .

The abstract base class of dictionaries

collections.abc There is Mapping and MutableMapping These two abstract base classes , Their function is to dict And other similar types define formal interfaces .

The italics in the table are abstract methods / class .

Class name Method / attribute Parent class
Container __contains__ -
Iterable __iter__ -
Sized __len__ -
Mapping __getitem__ , __contains__ , __eq__ , __ne__ , get , items , keys, values Container , Iterable , Sized
MutableMappint __setitem__ , __delitem__ , clear , pop , popitem , setdefault , update Mapping

dictdefaultdictOrderDict Method comparison

[] Is an optional parameter .

Method / object dict defaultdict OrderDict explain
d.clear() Yes Yes Yes Remove all elements
d.__contains__(k) Yes Yes Yes Check k Is it included in d in
d.copy() Yes Yes Yes Latent reproduction
d.__copy__() Yes Used to support copy.copy
d.default_factory Yes stay __missing__ The function called in the function , Used to set values for elements that are not found
d.__missing__(k) Yes When __getitem__ When the method cannot find the corresponding key , Call the method
d.__delitem__(k) Yes Yes Yes Remove key as k The elements of
d.fromkeys(it, [initial]) Yes Yes Yes Put the iterator it Set the element in the map to the key in the map , If there is initial Parameters , Just take it as the value corresponding to these keys ( The default is None
d.get(k, [default]) Yes Yes Yes Return key k Corresponding value , No, k When to return to default or None
d.__getitem__(k) Yes Yes Yes Make the dictionary usable d[k] Return key in the form of k Corresponding value
d.items() Yes Yes Yes Returns all key value pairs
d.__iter__() Yes Yes Yes Get the iterator of the key
d.keys() Yes Yes Yes Back to all keys
d.__len__() Yes Yes Yes It can be used len(d) Form to get the number of dictionary key value pairs
d.move_to_end(k, [last]) Yes Set the key to k Move the element of the test to the front or back position (last The default is True
d.pop(k, [default] Yes Yes Yes Return key k Corresponding value , And remove the key value pair . No, k When to return to default or None
d.popitem() Yes Yes Yes ( There are optional parameters last , The default is False , At this point, remove the earliest inserted key value pair , Otherwise, remove the last inserted key value pair ) Returns a random key value pair and removes it from the dictionary
d.__reversed__() Yes Iterators that return keys in reverse order
d.setdefault(k, [default]) Yes Yes Yes If there is a key in the dictionary k , Set its corresponding value to default , And then back to this value ; If there is no , Then let d[k] = default , Then return default
d.__setitem__(k, v) Yes Yes Yes Realization d[k] = v operation
d.update(m, [**kargs]) Yes Yes Yes m It can be a map or a key value pair iterator , Used to update d The corresponding entry in
d.values() Yes Yes Yes Returns all values in the dictionary

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