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Python Container Datatypes
In the collections there are some container datatypes, which are alternatives to python’s general purpose built-in containers like dict, list, set etc.
Some of the containers are −
| Sr.No. | Container & Description |
|---|---|
| 1 | namedtuple() Used to create tuple subclass with the name field |
| 2 | deque Queue using list type data |
| 3 | Counter Subclass of dict to count the hash-table objects |
| 4 | ChainMap Used to create single view of multiple mappings |
| 5 | OrderedDict Subclass of dict, where data are added in ordered manner |
| 6 | UserList Wrapper for list to easier access. |
To use this module, we should import it using −
import collections
Deque Object
The Deque is basically a generalization of stack and queue structure, where it is initialized from left to right. It uses the list object to create a deque.
Some Deque related methods are −
| Sr.No. | Methods & Description |
|---|---|
| 1 | append(x) Add element x at the right side of the deque |
| 2 | appendleft(x) Add element x at the left side of the deque |
| 3 | clear() Clear the deque |
| 4 | count(x) Count number of occurrences of x in the deque |
| 5 | index(x[, start[,stop]]) Return the position of x. If the start and stop are defined, it will find in that range |
| 6 | insert(i, x) Insert x into the deque at position i |
| 7 | pop() Remove and return element from the right side |
| 8 | popleft() Remove and return element from the left side |
| 9 | reverse() Reverse the contents of the deque |
| 10 | rotate(n = 1) Rotate deque n times to the right |
Example Code
import collections as col
my_deque = col.deque('124dfre')
print(my_deque)
print("Popped Item: " + str(my_deque.pop()))
print("Popped Item From Left: " + str(my_deque.popleft()))
print(my_deque)Output
deque(['1', '2', '4', 'd', 'f', 'r', 'e']) Popped Item: e Popped Item From Left: 1 deque(['2', '4', 'd', 'f', 'r'])
Counter Object
The counter is a subclass of a dict type object. It can be used to count the key values. The counters allow only integer value.
Some Counters related methods are −
| Sr.No. | Methods & Description |
|---|---|
| 1 | elements() Return the elements, that much times the counter value holds. |
| 2 | most_common([n]) This method returns a list of most commonly used n elements from the counter. If n is not specified, it will return all. |
| 3 | subtract(iterable or mapping) Subtract the counter value from two counter object, where keys are matched. |
| 4 | update(iterable or mapping) It adds the values without replacing the values, where keys are matched. |
Example Code
import collections as col text_list = ['ABC','PQR','ABC','ABC','PQR','Mno','xyz','PQR','ABC','xyz'] my_counter = col.Counter() for element in text_list: my_counter[element] += 1 print(my_counter) print(my_counter.most_common(2))
Output
Counter({'ABC': 4, 'PQR': 3, 'xyz': 2, 'Mno': 1})
[('ABC', 4), ('PQR', 3)]ChainMap Object
The ChainMap is used to encapsulates the dictionaries into single unit.
Some ChainMap members are −
| Sr.No. | Methods & Description |
|---|---|
| 1 | maps It is used to return keys with its corresponding values. |
| 2 | new_child(m = None) This method is used to insert a new dictionary at the first position of the chain. |
Example Code
import collections as col
con_code1 = {'India' : 'IN', 'China' : 'CN'}
con_code2 = {'France' : 'FR', 'United Kingdom' : 'GB'}
code = {'Japan' : 'JP'}
chain = col.ChainMap(con_code1, con_code2)
print("Initial Chain: " + str(chain.maps))
chain = chain.new_child(code) #Insert New Child
print("Final Chain: " + str(chain.maps))Output
Initial Chain: [{'India': 'IN', 'China': 'CN'}, {'France': 'FR', 'United Kingdom': 'GB'}]
Final Chain: [{'Japan': 'JP'}, {'India': 'IN', 'China': 'CN'}, {'France': 'FR', 'United Kingdom': 'GB'}]
Updated on: 30-Jul-2019
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