Python Tutorial

The Python collection module is defined as a container that is used to store collections of data, for example - list, dict, set, and tuple, etc. It was introduced to improve the functionalities of the built-in collection containers.

Python collection module was first introduced in its 2.4 release.

There are different types of collection modules which are as follows:

namedtuple()

The Python namedtuple() function returns a tuple-like object with names for each position in the tuple. It was used to eliminate the problem of remembering the index of each field of a tuple object in ordinary tuples.

Examples

pranshu = ('James', 24, 'M')  
print(pranshu)  

Output:

('James', 24, 'M')

OrderedDict()

The Python OrderedDict() is similar to a dictionary object where keys maintain the order of insertion. If we try to insert key again, the previous value will be overwritten for that key.

Example

import collections  
d1=collections.OrderedDict()  
d1['A']=10  
d1['C']=12  
d1['B']=11  
d1['D']=13  
  
for k,v in d1.items():  
    print (k,v)  

Output:

A 10
C 12
B 11
D 13

defaultdict()

The Python defaultdict() is defined as a dictionary-like object. It is a subclass of the built-in dict class. It provides all methods provided by dictionary but takes the first argument as a default data type.

Example

from collections import defaultdict    
number = defaultdict(int)    
number['one'] = 1    
number['two'] = 2    
print(number['three'])  

Output:

Counter()

The Python Counter is a subclass of dictionary object which helps to count hashable objects.

Example

from collections import Counter    
c = Counter()  
list = [1,2,3,4,5,7,8,5,9,6,10]    
Counter(list)  
Counter({1:5,2:4})    
list = [1,2,4,7,5,1,6,7,6,9,1]    
c = Counter(list)    
print(c[1])   

Output:

deque()

The Python deque() is a double-ended queue which allows us to add and remove elements from both the ends.

Example

from collections import deque  
list = ["x","y","z"]  
deq = deque(list)  
print(deq)  

Output:

deque(['x', 'y', 'z'])

Chainmap Objects

A chainmap class is used to groups multiple dictionary together to create a single list. The linked dictionary stores in the list and it is public and can be accessed by the map attribute. Consider the following example.

Example

from collections import ChainMap
baseline = {'Name': 'Peter', 'Age': '14'}
adjustments = {'Age': '14', 'Roll_no': '0012'}
print(list(ChainMap(adjustments, baseline)))

Output:

['Name', 'Age', 'Roll_no' ]

UserDict Objects

The UserDict behaves as a wrapper around the dictionary objects. The dictionary can be accessed as an attribute by using the UserDict object. It provides the easiness to work with the dictionary.

It provides the following attribute.

data - A real dictionary used to store the contents of the UserDict class.

UserList Objects

The UserList behaves as a wrapper class around the list-objects. It is useful when we want to add new functionality to the lists. It provides the easiness to work with the dictionary.

It provides the following attribute.

data - A real list is used to store the contents of the User class.

UserString Objects

The UserList behaves as a wrapper class around the list objects. The dictionary can be accessed as an attribute by using the UserString object. It provides the easiness to work with the dictionary.

It provides the following attribute.

data - A real str object is used to store the contents of the UserString class.

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